Unified State Examination tasks in chemistry with solutions: Interrelation of various classes of inorganic substances. Colorless bright red Formation of a colorless solution and evolution of gas
A solution of substance Y was added to a test tube with a solution of salt X. As a result, a reaction occurred, which is described by the following abbreviated ionic equation S 2- + 2H + = H 2 S. From the proposed list, select substances X and Y that can enter into the described reaction.
1) sodium sulfide;
2) carbonic acid;
3) hydrogen chloride;
4) iron (II) sulfide;
5) potassium sulfite;
A solution of substance Y was added to a test tube with a solution of salt X. As a result of the reaction, the formation of a white precipitate was observed,
1) potassium nitrate;
2) barium chloride;
H) hydrochloric acid;
4) calcium carbonate;
5) sulfuric acid;
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of substance Y was added to a test tube with a solution of sodium salt X. As a result, a reaction occurred that is described by the following abbreviated ionic equation:
S 2- + Fe 2+ = FeS.
From the proposed list, select substances X and Y that can enter into the reaction described.
1) sodium sulfide;
2) sodium sulfite;
3) hydrogen sulfide;
4) iron (II) hydroxide;
5) iron (II) sulfate;
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of substance Y was added to a test tube with a solution of salt X. As a result of the reaction, the release of a colorless gas was observed. From the proposed list, select substances X and Y that can enter into the reaction described.
1) potassium sulfite;
2) sodium hydroxide;
H) iron(II) sulfate;
4) hydrogen chloride;
5) sodium nitrate.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of acid Y was added to a test tube with a solution of substance X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: OH - + H + = H 2 O.
From the proposed list, select substances X and Y that can enter into the reaction described.
1) sodium sulfide;
2) carbonic acid;
3) sulfuric acid;
4) barium hydroxide;
5) potassium hydroxide.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of salt Y was added to a test tube containing a solution of substance X. As a result of the reaction, a blue precipitate formed. From the proposed list, select substances X and Y that can enter into the reaction described.
1) iron(II) sulfate;
2) hydrochloric acid;
3) sodium hydroxide;
4) calcium nitrate;
5) copper (II) sulfate.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of substance Y was added to a test tube with a solid, water-insoluble substance X. As a result of the reaction, the dissolution of the solid without the release of gas was observed. From the proposed list, select substances X and Y that can enter into the reaction described.
1) calcium carbonate;
2) sodium hydroxide;
H) barium sulfate;
4) sulfuric acid;
5) copper(II) oxide.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of salt Y was added to a test tube with a solution of substance X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: CO 3 2- + 2H + = H 2 O + CO 2.
From the proposed list, select substances X and Y that can enter into the described reaction.
1) calcium bicarbonate;
2) calcium hydroxide;
3) acetic acid;
4) sulfuric acid;
5) sodium carbonate.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of salt Y was added to a test tube with a solution of substance X. As a result of the reaction, the formation of a brown precipitate was observed. From the proposed list, select substances X and Y that can enter into the reaction described.
1) copper(II) chloride;
2) hydrochloric acid;
3) sodium hydroxide;
4) sodium nitrate;
5) iron(III) sulfate.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of substance Y was added to a test tube with a solution of acid X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: SO 3 2- + 2H + = H 2 O + SO 2.
From the proposed list, select substances X and Y that can enter into the reaction described.
1) potassium sulfate;
2) hydrosulfide acid;
3) sulfuric acid;
4) ammonium sulfide;
5) sodium sulfite.
Write down the numbers of the selected substances under the corresponding letters in the table.
Zinc was completely dissolved in concentrated sodium hydroxide solution. The resulting clear solution of substance X was evaporated and then calcined. In this case, solid substance Y was formed. From the proposed list, select substances X and Y that correspond to the given description.
1) Na 2 ZnO 2;
2) Zn(OH) 2;
3) ZnO;
4) Na 2;
5) NaOH.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of sodium chloride was mixed with a solution of salt X. The white precipitate that formed was separated, the solution was evaporated, the remaining dry salt was calcined in air, and colorless gas Y was released. From the proposed list, select substances X and Y that correspond to the description given.
1) AgNO 3;
2) HNO 3;
3) Na 2 CO 3;
4) CO 2;
5) O 2.
Write down the numbers of the selected substances under the corresponding letters in the table.
Aluminum nitrate was calcined. The resulting solid X was fused with excess potassium hydroxide. The resulting melt was treated with excess water, which resulted in the formation of a transparent solution of substance Y. From the proposed list, select substances X and Y that correspond to the description given.
1) Al;
2) Al 2 O 3;
3) KAlO 2;
4) K;
5) K 3 AlO 3 .
Write down the numbers of the selected substances under the corresponding letters in the table.
Iron (II) hydroxide was converted to peroxide. The resulting brown substance X was fused with solid potassium hydroxide. The resulting melt containing salt Y was treated with excess water, as a result of which brown substance X was again obtained. From the proposed list, select substances X and Y that correspond to the description given.
1) Fe 2 O 3;
2) Fe(OH) 3;
3) KFeO 2;
4) FeO;
5) K 3 FeO 3;
Write down the numbers of the selected substances under the corresponding letters in the table.
Aluminum hydroxide was fused with potassium hydroxide. The resulting salt X was treated with an excess of hydrochloric acid, which resulted in the formation of substance Y. From the proposed list, select substances X and Y that correspond to the description given.
1) K;
2) KAlO 2;
3) K 3 AlO 3;
4) AlCl 3;
5) Al(ClO 4) 3;
Write down the numbers of the selected substances under the corresponding letters in the table.
Potassium sulfite was treated with hydrochloric acid. The resulting gas X was absorbed by an excess of calcium hydroxide, and substance Y was formed. From the proposed list, select substances X and Y that correspond to the description given.
1) H 2 S;
2) CaS;
3) Ca(HSO 3) 2;
4) SO 2;
5) CaSO 3 .
Write down the numbers of the selected substances under the corresponding letters in the table.
Strong acid X was added to one of the test tubes with a precipitate of aluminum hydroxide, and a solution of substance Y was added to the other. As a result, dissolution of the precipitate was observed in each of the test tubes. From the proposed list, select substances X and Y that can enter into the described reactions.
1) hydrobromic acid;
2) sodium hydrosulfide;
3) hydrosulfide acid;
4) potassium hydroxide;
5) ammonia hydrate.
Write down the numbers of the selected substances under the corresponding letters in the table.
Silver nitrate was calcined. Concentrated nitric acid was added to the resulting solid residue X, and intense evolution of gas Y was observed. From the proposed list, select substances X and Y that correspond to the description given.
1) silver(I) oxide;
2) silver nitrite;
3) silver;
4) nitric oxide (II);
5) nitric oxide (IV).
Write down the numbers of the selected substances under the corresponding letters in the table.
Silver bromide was heated with zinc powder. The resulting salt was dissolved in water. A solution of potassium hydroxide was added dropwise to the resulting solution. First, a white precipitate X formed, and then, when a new portion of the potassium hydroxide solution was added, it completely dissolved with the formation of substance Y. From the proposed list, select substances X and Y that correspond to the description given.
1) Ag;
2) ZnBr 2;
3) Zn(OH) 2;
4) K 2 ZnO 2 ;
5) K 2.
Write down the numbers of the selected substances under the corresponding letters in the table.
Phosphorus(V) chloride was added to an excess of barium hydroxide solution. The precipitate X was separated, dried and calcined with sand and coal, and substance Y was formed. From the proposed list, select substances X and Y that correspond to the description given.
1) Ba 3 (PO 4) 2;
2) BaHPO 4;
3) BaCl 2;
4) CO 2;
5) CO.
Write down the numbers of the selected substances under the corresponding letters in the table.
Sodium dichromate reacted with sodium hydroxide. The resulting substance X was treated with sulfuric acid, and the orange substance Y was isolated from the resulting solution. From the proposed list, select substances X and Y that correspond to the given description.
1) Na 2 Cr 2 O 7;
2) Na 2 CrO 4 ;
3) NaCrO 2;
4) Na 3;
5) Na 2 SO 4.
Write down the numbers of the selected substances under the corresponding letters in the table.
Copper(II) sulfate was added to the barium chloride solution. The resulting precipitate X was filtered off. Potassium iodide was added to the remaining solution, and the formation of precipitate Y and a change in the color of the solution were observed. From the proposed list, select substances X and Y that correspond to the given description.
1) BaSO 3;
2) BaSO 4;
3) CuI 2;
4) CuI;
5) KCl;
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of substance Y was added to a test tube with an alkali solution (substance X). As a result, a reaction occurred, which is described by the abbreviated ionic equation OH – + H + = H 2 O. From the proposed list, select substances X and Y that can enter into the described reaction.
1) potassium sulfide;
2) carbonic acid;
3) sulfuric acid;
4) barium hydroxide;
5) sodium hydroxide.
Write down the numbers of the selected substances under the corresponding letters in the table.
As a result of the interaction of a solution of copper(II) sulfate with iron, salt X was formed. This salt was heated with concentrated sulfuric acid, resulting in the formation of a new salt Y. From the proposed list, select substances X and Y that correspond to the description given.
1) FeS;
2) CuS;
3) FeSO 4;
4) FeSO 3;
5) Fe 2 (SO 4) 3.
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of sodium sulfide was added to a solution of iron(III) chloride, resulting in a precipitate. The resulting precipitate was treated with a solution of sulfuric acid, and part of the precipitate X dissolved. The undissolved part of precipitate Y was yellow. From the proposed list, select substances X and Y that correspond to the given description.
1) FeS;
2) Fe(OH) 2;
3) Fe 2 S 3;
4) S;
5) Fe(OH) 3 .
Write down the numbers of the selected substances under the corresponding letters in the table.
Iron(III) chloride was added to a solution of sodium hydroxide, and precipitate X formed. The precipitate was separated and dissolved in hydroiodic acid. In this case, substance Y was formed. From the proposed list, select substances X and Y that correspond to the given description.
1) Fe(OH) 2;
2) Fe(OH) 3;
3) FeI 3;
4) I 2;
5) NaCl;
Write down the numbers of the selected substances under the corresponding letters in the table.
Excess carbon dioxide was passed through a solution of sodium hydroxide. The resulting substance X was isolated from the solution, dried and calcined. This resulted in the formation of solid substance Y. From the proposed list, select substances X and Y that correspond to the description given.
1) Na 2 CO 3;
2) NaHCO 3;
3) HCOONa;
4) Na 2 O 2;
5) Na 2 O.
Write down the numbers of the selected substances under the corresponding letters in the table.
Substance X was added to one test tube with a solution of copper(II) chloride, and as a result of the reaction, the formation of a red precipitate was observed. A solution of substance Y was added to another test tube with a solution of copper(II) chloride. As a result of the reaction, an insoluble salt was formed. From the proposed list, select substances X and Y that can enter into the described reactions.
1) zinc;
2) zinc oxide;
3) potassium bromide;
4) silver fluoride;
5) silver.
Write down the numbers of the selected substances under the corresponding letters in the table.
A few drops of a solution of salt X were added to one of the test tubes with a solution of iron (III) sulfate, and a solution of substance Y was added to the other. As a result, a brown precipitate formed in each of the test tubes. From the proposed list, select substances X and Y that can enter into the described reactions.
1) BaCl 2;
2) NH 3;
3) Cu(OH) 2;
4) K 2 CO 3;
5) AgNO 3;
Write down the numbers of the selected substances under the corresponding letters in the table.
A solution of salt X was added to one of the test tubes with hydrochloric acid, and substance Y was added to the other. As a result, the release of a colorless, odorless gas was observed in each of the test tubes. From the proposed list, select substances X and Y that can enter into the described reactions.
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Reference material for taking the test:
Periodic table
Solubility table
The types of questions that appear in this test (you can see the answers to the questions and the full conditions of the tasks by passing the test above to the end. We recommend looking at how to solve these questions in our):
- A solution of substance Y was added to a test tube with a solution of salt X. As a result, a reaction occurred that is described by the abbreviated ionic equation ____. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of substance Y was added to a test tube with a solution of salt X. As a result of the reaction, a white precipitate formed. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of substance Y was added to a test tube with a solution of potassium salt X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: ____. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of substance Y was added to a test tube with a solution of salt X. As a result of the reaction, the release of a colorless gas was observed. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of acid Y was added to a test tube with a solution of substance X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: ____. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of salt Y was added to a test tube containing a solution of substance X. As a result of the reaction, a blue precipitate formed. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of substance Y was added to a test tube containing a water-insoluble solid substance X. As a result of the reaction, the solid substance dissolved without gas evolution. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of salt Y was added to a test tube containing a solution of substance X. As a result, a reaction occurred that is described by the following abbreviated ionic equation: ____. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of salt Y was added to a test tube containing a solution of substance X. As a result of the reaction, a brown precipitate formed. From the proposed list, select substances X and Y that can enter into the described reaction.
- A solution of substance Y was added to a test tube with a solution of acid X. As a result, a reaction occurred that is described by the following abbreviated ionic equation. From the proposed list, select substances X and Y that can enter into the described reaction.
Solving the problems of part C2
1. A mixture of two colorless and odorless gases, A and B, was passed through when heated over a catalyst containing iron. The resulting gas B was passed into a solution of hydrobromic acid, and a neutralization reaction occurred. The solution was evaporated and the residue was heated with caustic potassium, resulting in the release of colorless gas B with a pungent odor. When gas B is burned in air, water and gas A are formed. Write the equation for the reactions described.
Solution
An acid solution can be neutralized with a substance that exhibits basic properties. Since when the reaction product with caustic potassium was heated, a gas with a pungent odor and a gas with basic properties were released, this gas is ammonia NH 3.
1 equation - synthesis of ammonia from nitrogen and hydrogen;
Equation 2 - acid neutralization;
3 equation - qualitative reaction to ammonia with alkali;
Equation 4 - combustion of ammonia in air, releasing nitrogen
Gases - N 2, H 2 and NH 3.
1) N 2 + 3H 2 ↔ 2NH 3
2) NH 3 + HBr = NH 4 Br
3) NH 4 Br + KOH = KBr + H 2 O + NH 3
4) 4NH 3 + 3O 2 = 2N 2 + 6 H 2 O
2. Pass sulfur dioxide through a solution of hydrogen peroxide. The water was evaporated and magnesium shavings were added to the residue. The released gas was passed through a solution of copper sulfate. The resulting black precipitate was separated and fired. Write the equation for the reactions described.
Solution
In sulfur dioxide, the oxidation state of sulfur is +4. Therefore, it can be both an oxidizing agent and a reducing agent. With a strong oxidizing agent, sulfur will be a reducing agent and will increase the oxidation state to +6 (i.e., H will be formed 2 SO 4 ) (1 equation).
After evaporation H 2 O, concentrated sulfuric acid is formed, which, when interacting with Mg (active metal), produces hydrogen sulfide (2). Copper sulfate - II, reacting with hydrogen sulfide, will give copper sulfide - a black precipitate (3). When sulfides are roasted, sulfur oxide (IV) and metal oxide (4) are formed.
1) SO 2 + H 2 O 2 = H 2 SO 4
2) 5H 2 SO 4 conc. + 4Mg = 4MgSO 4 + H 2 S + 4H 2 O
3) H 2 S + CuSO 4 = CuS↓ + H 2 SO 4
4) 2CuS + 3O 2 = 2CuO + 2SO 2
3. When a certain mineral A, consisting of 2 elements, is fired, a gas is formed that has a pungent odor and discolors bromine water with the formation of two strong acids in solution. When substance B, consisting of the same elements as mineral A, but in a different ratio, interacts with concentrated hydrochloric acid, a gas with the smell of “rotten eggs” is released. When gases interact with each other, a simple yellow substance and water are formed. Write the equations for the reactions described.
Solution
Since when substance B is exposed to hydrochloric acid, hydrogen sulfide H is released 2 S (a gas with a “rotten egg” odor) (Equation 3), then both minerals are sulfides. The roasting of FeS pyrite is being studied in the sulfuric acid production process. 2 (1). SO 2 – a gas with a pungent odor exhibits propertiesa reducing agent and reacting with bromine water produces two acids: sulfuric and hydrobromic (2). When sulfur dioxide (oxidizing agent) and hydrogen sulfide (reducing agent) interact, sulfur is formed - a simple yellow substance (4).
1) 4FeS 2 + 11O 2 = 2Fe 2 O 3 + 8SO 2
2) SO 2 + Br 2 + 2H 2 O = H 2 SO 4 + 2HBr
3) FeS + 2HCl = FeCl 2 + H 2 S
4) SO 2 + 2H 2 S = 3S↓ + 2H 2 O
4. Nitric acid was neutralized with baking soda, the solution was evaporated and the residue was calcined. The resulting substance was added to a solution of potassium permanganate acidified with sulfuric acid, and the solution became colorless. The nitrogen-containing reaction product was placed in a solution of caustic soda and zinc dust was added, and a gas with a sharp characteristic odor was released. Write the equations for the reactions described.
Solution
After neutralization of the solution, sodium nitrate is formed (1). Nitrates formed by metals in the voltage series to the left of Mg decompose to form nitrites and oxygen (2). Potassium permanganate KMnO 4 , which has a pink color, is a strong oxidizing agent in an acidic environment and oxidizes sodium to NaN nitrate+5 O 3 , itself is reduced to Mn+2 (colorless) (3). When zinc reacts with an alkali solution, atomic hydrogen is released, which is a very strong reducing agent, therefore sodium nitrate NaN+5 O 3 is reduced to ammonia N-3 H 3 (4).
1) HNO 3 + NaHCO 3 = NaNO 3 + H 2 O + CO 2
2) 2 NaNO 3 = 2NaNO 2 + O 2
3) 5NaNO 2 + 2KMnO 4 + 3H 2 SO 4 = 5NaNO 3 + K 2 SO 4 + 2MnSO 4 + 3H 2 O
4) NaNO 3 + 4Zn+ 7NaOH + 6H 2 O = NH 3 + 4Na 2 Zn(OH) 4
5. An unknown metal was burned in oxygen. The reaction product, interacting with carbon dioxide, forms two substances: a solid that reacts with a solution of hydrochloric acid to release carbon dioxide, and a gaseous simple substance that supports combustion. Write the equations for the reactions described.
Solution
The gas that supports combustion is oxygen (4). When metals burn in oxygen, oxides and peroxides can form. Oxides will give only one substance when interacting with carbon dioxide - a carbonate salt, so we take an alkali metal, sodium, which forms peroxide (1). When reacting with carbon dioxide, salt is formed and oxygen is released (2). Carbonate with acid produces carbon dioxide (3).
1) 2Na + O 2 = Na 2 O 2
2) 2Na 2 O 2 + 2CO 2 = 2Na 2 CO 3 + O 2
3) Na 2 CO 3 + 2HCl = 2NaCl + H 2 O + CO 2
4) O 2 +C = CO 2.
6. Trivalent chromium hydroxide was treated with hydrochloric acid. Potash was added to the resulting solution, the precipitate that formed was separated and added to a concentrated solution of potassium hydroxide, as a result of which the precipitate dissolved. After adding excess hydrochloric acid, a green solution was obtained. Write the equations for the reactions described.
Solution
Chromium hydroxide Cr(OH) 3 - amphoteric. With hydrochloric acid will give CrCl 3 (1), the salt is formed by a weak base and a strong acid, so it will undergo cationic hydrolysis. Potash - potassium carbonate K 2 CO 3 formed by a strong base and a weak acid, undergoes hydrolysis at the anion. The two salts mutually enhance the hydrolysis of each other, so the hydrolysis proceeds to the end: until the formation of Cr(OH) 3 and CO 2 (2). Cr(OH)3 in excess of alkali gives potassium hexahydroxochromite K 3 Cr(OH) 6 (3). When exposed to an excess of strong acid, two salts are formed (4).
1) Cr(OH) 3 + 3HCl = CrCl 3 + 3H 2 O
2) CrCl 3 + 3K 2 CO 3 + 3H 2 O = 2Cr(OH) 3 ↓ + 3CO 2 + 6KCl
3) Cr(OH) 3 + 3KOH conc. = K 3 Cr(OH) 6
4) K 3 Cr(OH) 6 + 6HCl = CrCl 3 + 3KCl + 6H 2 O.
7. The product of the reaction of lithium with hydrogen was treated with water. The released gas was mixed with excess oxygen and passed over a platinum catalyst while heating; formed gas mixture had a brown color. Write the equations for the reactions described.
Solution
The interaction of nitrogen and lithium produces lithium nitride (1), which decomposes with water to release ammonia (2). Ammonia is oxidized by oxygen in the presence of a platinum catalyst to nitrogen oxide (II), which has no color (3). Formation of brown gas NO 2 from NO occurs spontaneously (4).
1) 6Li + N 2 = 2Li 3 N
2) Li 3 N + 3H 2 O = 3LiOH + NH 3
3) 4NH 3 + 5O 2 = 4NO + 6H 2 O
4) 2NO + O 2 = 2NO 2.
8. Magnesium silicide was treated with a solution of hydrochloric acid and the resulting gas was burned. The solid reaction product was mixed with soda ash, the mixture was heated until melting and kept for some time. After cooling, the reaction product (used under the name “liquid glass”) was dissolved in water and treated with a solution of sulfuric acid. Write equations for descriptive reactions.
Solution
When magnesium silicide reacts with hydrochloric acid, silane gas (1) is formed. It ignites spontaneously in air, producing silica (solid) and water (2). When silicon oxide is fused with alkali or soda, sodium silicate (“liquid glass”) is formed (3). Sulfuric acid, being stronger, displaces weak silicic acid from solution, which is insoluble in water (4).
1) Mg 2 Si + 4HCl = 2MgCl 2 + SiH 4
2) 2SiH 4 + 2O 2 = SiO 2 + 2H 2 O
3) SiO 2 + Na 2 CO 3 = Na 2 SiO 3 + CO 2
4) Na 2 SiO 3 + H 2 SO 4 = Na 2 SO 4 + H 2 SiO 3 ↓.
9. When the orange substance is heated, it decomposes; decomposition products include a colorless gas and a green solid. The released gas reacts with lithium even with slight heating. The product of the latter reaction reacts with water, releasing a gas with a pungent odor that can reduce metals, such as copper, from their oxides. Write the equations for the reactions described.
Solution
A gas with a pungent odor that can reduce metals from their oxides (equation 4) is ammonia (equation 3). An orange substance that decomposes to release nitrogen (a colorless gas) and form a green solid, Cr. 2 O 3 - ammonium dichromate (NH 4) 2 Cr 2 O 7 (equation 1), when lithium nitride reacts with water, ammonia is released (3).
1) (NH 4 ) 2 Cr 2 O 7 = t N 2 + 4H 2 O + Cr 2 O 3
2) N 2 + 6Li = 2Li 3 N
3) Li 3 N + 3H 2 O = 3LiOH + NH 3
4) 2NH 3 + 3CuO = N 2 + 3Cu + 3H 2 O.
10. An unknown red substance was heated in chlorine and the reaction product was dissolved in water. Alkalies were added to the resulting solution, the resulting blue precipitate was filtered and calcined. When the calcination product, which is black in color, was heated with coke, a red starting material was obtained. Write the equations for the reactions described.
Solution
Red metal - copper. When heated with chlorine, copper-II chloride CuCl is formed 2 (1). When alkali is added to a solution, a gelatinous blue precipitate Cu(OH) precipitates. 2 - copper-II hydroxide (2). When heated, it decomposes into black copper-II oxide (3). When the oxide is heated with coke (C), copper is reduced.
1) Cu + Cl 2 = CuCl 2
2) CuCl 2 + 2NaOH = Cu(OH) 2 ↓ + 2NaCl
3) Cu(OH) 2 = CuO + H 2 O
4) CuO + C = Cu + CO.
11. The salt obtained by reacting zinc oxide with sulfuric acid was calcined at 800 O C. The solid reaction product was treated with a concentrated alkali solution and carbon dioxide was passed through the resulting solution. Write the reaction equations for the transformations described.
Solution
When zinc oxide reacts with sulfuric acid, the salt zinc sulfate ZnSO is obtained 4 (1). At high temperatures, many metal sulfates decompose to form metal oxide, sulfur dioxide, and oxygen (2). Zinc oxide is amphoteric, therefore it reacts with alkali, forming sodium tetrahydroxyzincate Na 2 Zn(OH) 4 (3). When carbon dioxide is passed into water, carbonic acid is formed, which destroys the complex, and a precipitate of zinc hydroxide is formed (4).
1) ZnO + H 2 SO 4 = ZnSO 4 + H 2 O
2) 2ZnSO 4 = 2ZnO + SO 2 + O 2
3) ZnO + 2NaOH + H 2 O = Na 2 Zn(OH) 4
4) Na 2 Zn(OH) 4 + CO 2 = Na 2 CO 3 + Zn(OH) 2 ↓ + H 2 O.
12. Copper shavings were added to a solution of mercury-II nitrate. The solution was filtered and the filtrate was added dropwise to a solution containing sodium hydroxide and ammonium hydroxide. In this case, a short-term formation of a precipitate was observed, which dissolved to form a bright blue solution. When an excess of sulfuric acid solution was added to the resulting solution, a color change occurred. Write the equation for the reactions described.
Solution
Copper is in the series of metal stresses to the left of mercury, therefore it displaces it from the salt solution (1). When a solution of copper-II nitrate is added to alkali, insoluble copper-II hydroxide Cu(OH) is formed 2 (2), which dissolves in excess ammonia, forming a bright blue complex compound Cu(NH 3 ) 4 (OH) 2 (3). When sulfuric acid is added, it is destroyed and the solution turns blue (4).
1) Hg(NO 3 ) 2 + Cu = Ng + Cu(NO 3 ) 2
2) Cu(NO 3 ) 2 + 2KOH = Cu(OH) 2 ↓ + 2KNO 3
3) Cu(OH) 2 + 4NH 4 OH = Cu(NH 3 ) 4 (OH) 2 + 4H 2 O
4) Cu(NH 3 ) 4 (OH) 2 + 5H 2 SO 4 = CuSO 4 + 4NH 4 HSO 4 + 2H 2 O
acidic salt is formed, because excess acid.
13. Red phosphorus was burned in an atmosphere of chlorine and a few drops of water were added to the reaction product. The released substance was dissolved in excess water, iron powder was added to the resulting solution, and the gaseous reaction product was passed over a heated copper plate oxidized to cuprous oxide. Write the reaction equations for the transformations described.
Solution
When phosphorus burns in excess chlorine, phosphorus chloride-V PCl is formed 5 (1). During hydrolysis with a small amount of water, hydrogen chloride is released and metaphosphoric acid is formed (2). Iron displaces hydrogen from acid solutions (3). Hydrogen reduces metals from their oxides (4).
1) 2P + 5Cl 2 = 2PCl 5
2) PCl 5 + 3H 2 O = HPO 3 + 5HCl
3) Fe + 2HCl = FeCl 2 + H 2
4) CuO + H 2 = t Cu + H 2 O.
14. The substance obtained by heating iron scale in a hydrogen atmosphere was added to hot concentrated sulfuric acid and heated it up. The resulting solution was evaporated, the residue was dissolved in water and treated with a solution of barium chloride. The solution was filtered and a copper plate was added to the filtrate, which dissolved after some time. Write the equations for the reactions described.
Solution
When heating metal oxides, in particular iron scale Fe 3 O 4, with hydrogen metals are reduced (1). Iron does not react with concentrated sulfuric acid under normal conditions, but when heated it dissolves (2). Iron-III sulfate with barium chloride forms a precipitate of barium sulfate (30). Iron-III chloride exhibits oxidizing properties and dissolves copper (4).
1) Fe 3 O 4 + 8H 2 = 3Fe + 4H 2 O
2) 2Fe + 6H 2 SO 4conc. (hor.) = Fe 2 (SO 4 ) 3 + 3SO 2 + 6H 2 O
3) Fe 2 (SO 4 ) 3 + 3BaCl 2 = 3BaSO 4 ↓ + 2FeCl 3
4) 2FeCl 3 + Cu = 2FeCl 2 + CuCl 2.
15. Quicklime was calcined with excess coke. The reaction product after treatment with water is used to absorb sulfur dioxide and carbon dioxide. Write the equations for the reactions described.
Solution
Calcination of quicklime with coke is an industrial method for producing calcium carbide (1). When calcium carbide is hydrolyzed, acetylene is released and calcium hydroxide (2) is formed, which can react with acid oxides (3, 4).
1) CaO + 3C = CaC 2 + CO
2) CaC 2 + 2H 2 O = Ca(OH) 2 ↓ + C 2 H 2
3) Ca(OH) 2 + SO 2 = CaSO 3 ↓ + H 2 O
4) Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O.
16. Electrical discharges were passed over the surface of a caustic soda solution poured into a flask, and the air in the flask turned brown, which disappeared after some time. The resulting solution was carefully evaporated and it was determined that the solid residue was a mixture of two salts. When this mixture is heated, gas is released and the only substance remains. Write the equations for the reactions described.
Solution
During electrical discharges, nitrogen reacts with oxygen to form a colorless gas of nitric oxide (1), which is spontaneously quickly oxidized by atmospheric oxygen to brown nitric oxide-IV (2). Nitric oxide-IV, dissolving in alkali, forms two salts - nitrate and nitrite, because is an anhydride of two acids (3). When heated, nitrate decomposes to form nitrite and release oxygen (4).
1) N 2 + O 2 = 2NO
2) 2NO + O 2 = 2NO 2
3) 2NO 2 + 2NaOH = NaNO 3 + NaNO 2 + H 2 O
4) 2NaNO 3 = 2NaNO 2 + O 2.
17. A solution of hydrochloric acid was carefully added to the pyrolusite. The released gas was passed into a beaker half filled with a cold solution of potassium hydroxide. After the reaction was completed, the glass was covered with cardboard and left in the light; after a while they brought in a smoldering splinter, which flared up brightly. Write the equations for the reactions described.
Solution
Interaction of hydrochloric acid with pyrolusite MnO 2 - laboratory method for producing chlorine (1). Chlorine in a cold solution of potassium hydroxide gives two salts: potassium chloride and potassium hypochlorite (2). Hypochlorite is an unstable substance and, when illuminated, decomposes with the release of oxygen (3), the formation of which is proven with the help of a flashing splinter (4).
1) MnO 2 + 4HCl = Cl 2 + MnCl 2 + 2H 2 O
2) Cl 2 + 2KOH = KCl + KClO + H 2 O
3) 2KClO = 2KCl + O 2
4) C + O 2 = CO 2.
The proposed material presents methodological developments of practical work for the 9th grade: “Solving experimental problems on the topic “Nitrogen and Phosphorus”, “Determination of mineral fertilizers”, as well as laboratory experiments on the topic “Exchange reactions between electrolyte solutions”.
Exchange reactions between electrolyte solutions
Methodological development consists of three parts: theory, practical work, control. The theoretical part provides some examples of molecular, full and abbreviated ionic equations chemical reactions, proceeding with the formation of a precipitate, a poorly dissociating substance, and the release of gas. The practical part contains tasks and recommendations for students on how to perform laboratory experiments. The control consists of test tasks with the choice of the correct answer.
Theory
1. Reactions leading to the formation of a precipitate.
a) When copper(II) sulfate reacts with sodium hydroxide, a blue precipitate of copper(II) hydroxide is formed.
CuSO 4 + 2NaOH = Cu(OH) 2 + Na 2 SO 4.
Cu 2+ + + 2Na + + 2OH – = Cu(OH) 2 + 2Na + + ,
Cu 2+ + 2OH – = Cu(OH) 2.
b) When barium chloride reacts with sodium sulfate, a white milky precipitate of barium sulfate precipitates.
Molecular equation of a chemical reaction:
BaCl 2 + Na 2 SO 4 = 2NaCl + BaSO 4.
Full and abbreviated ionic reaction equations:
Ba 2+ + 2Cl – + 2Na + + = 2Na + + 2Cl – + BaSO 4 ,
Ba 2+ + = BaSO 4 .
2.
When sodium carbonate or bicarbonate (baking soda) interacts with hydrochloric or other soluble acid, boiling or intense release of gas bubbles is observed. This releases carbon dioxide CO 2, causing cloudiness in the clear solution of lime water (calcium hydroxide). Lime water becomes cloudy because... insoluble calcium carbonate is formed.
a) Na 2 CO 3 + 2HCl = 2NaCl + H 2 O + CO 2;
b) NaHCO 3 + HCl = NaCl + CO 2 + H 2 O;
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O.
a) 2Na + + + 2H + + 2Cl – = 2Na + + 2Cl – + CO 2 + H 2 O,
2H + = CO 2 + H 2 O;
b) Na + + + H + + Cl – = Na + + Cl – + CO 2 + H 2 O,
H + = CO 2 + H 2 O.
3. Reactions that occur with the formation of a slightly dissociating substance.
When sodium or potassium hydroxide reacts with hydrochloric acid or other soluble acids in the presence of the phenolphthalein indicator, the alkali solution becomes colorless, and as a result of the neutralization reaction, a low-dissociating substance H 2 O is formed.
Molecular equations of chemical reactions:
a) NaOH + HCl = NaCl + H 2 O;
c) 3KOH + H 3 PO 4 = K 3 PO 4 + 3H 2 O.
Full and abbreviated ionic reaction equations:
a) Na + + OH – + H + + Cl – = Na + + Cl – + H 2 O,
OH – + H + = H 2 O;
b) 2Na + + 2OH – + 2H + + = 2Na + + + 2H 2 O,
2OH – + 2H + = 2H 2 O;
c) 3K + + 3OH – +3H + + = 3K + + + 3H 2 O,
3OH – + 3H + = 3H 2 O.
Workshop
1. Exchange reactions between electrolyte solutions leading to the formation of a precipitate.
a) Carry out a reaction between solutions of copper(II) sulfate and sodium hydroxide. Write molecular, complete and abbreviated ionic equations of chemical reactions, note the signs of a chemical reaction.
b) Carry out a reaction between solutions of barium chloride and sodium sulfate. Write molecular, complete and abbreviated ionic equations of chemical reactions, note the signs of a chemical reaction.
2. Reactions that involve the release of gas.
Carry out reactions between solutions of sodium carbonate or sodium bicarbonate (baking soda) with hydrochloric or other soluble acid. Pass the released gas (using a gas outlet tube) through clear lime water poured into another test tube until it becomes cloudy. Write molecular, complete and abbreviated ionic equations of chemical reactions, note the signs of these reactions.
3. Reactions that occur with the formation of a slightly dissociating substance.
Carry out neutralization reactions between alkali (NaOH or KOH) and acid (HCl, HNO 3 or H 2 SO 4), after placing phenolphthalein in the alkali solution. Note observations and write molecular, complete and abbreviated ionic equations for chemical reactions.
Signs, accompanying these reactions, can be selected from the following list:
1) release of gas bubbles; 2) sedimentation; 3) the appearance of odor; 4) dissolution of the sediment; 5) heat release; 6) change in the color of the solution.
Control (test)
1. Ionic equation The reaction in which a blue precipitate is formed is:
a) Cu 2+ + 2OH – = Cu(OH) 2;
c) Fe 3+ + 3OH – = Fe(OH) 3;
d) Al 3+ + 3OH – = Al(OH) 3.
2. The ionic equation for the reaction in which carbon dioxide is released is:
a) CaCO 3 + CO 2 + H 2 O = Ca 2+ +;
b) 2H + + SO 2- 3 = H 2 O + SO 2;
c) CO 2- 3 + 2H + = CO 2 + H 2 O;
d) 2H + + 2OH – = 2H 2 O.
3. The ionic equation of the reaction in which a low-dissociating substance is formed is:
a) Ag + + Cl – = AgCl;
b) OH – + H + = H 2 O;
c) Zn + 2H + = Zn 2+ + H 2;
d) Fe 3+ + 3OH – = Fe(OH) 3.
4. The ionic equation for the reaction that produces the white precipitate is:
a) Cu 2+ + 2OH – = Cu(OH) 2;
b) CuO + 2H + = Cu 2+ + H 2 O;
c) Fe 3+ + 3OH – = Fe(OH) 3;
d) Ba 2+ + SO 2- 4 = BaSO 4 .
5. The molecular equation that corresponds to the abbreviated ionic equation for the reaction 3OH – + 3H + = 3H 2 O is:
a) NaOH + HCl = NaCl + H 2 O;
b) 2NaOH + H 2 SO 4 = Na 2 SO 4 + 2H 2 O;
c) 3KOH + H 3 PO 4 = K 3 PO 4 + 3H 2 O;
d) Ba(OH) 2 + 2HCl = BaCl 2 + H 2 O.
6. Molecular equation that corresponds to the abbreviated ionic reaction equation
H + + = H 2 O + CO 2 , –
a) MgCO 3 + 2HCl = MgCl 2 + CO 2 + H 2 O;
b) Na 2 CO 3 + 2HCl = 2NaCl + CO 2 + H 2 O;
c) NaHCO 3 + HCl = NaCl + CO 2 + H 2 O;
d) Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O.
| Answers. 1 -A; 2 -V; 3 -b; 4 -G; 5 -V; 6 -V. |
Solving experimental problems on the topic “Nitrogen and Phosphorus”
When studying new material on the topic “Nitrogen and Phosphorus,” students perform a series of experiments related to the production of ammonia, the determination of nitrates, phosphates, and ammonium salts, and acquire certain skills and abilities. This methodological development contains six tasks. To complete practical work, three tasks are enough: one on obtaining a substance, two on recognizing substances. When performing practical work, students can be offered tasks in a form that will make it easier for them to prepare a report (see tasks 1, 2). (Answers are given for the teacher.)
Task 1
Obtain ammonia and experimentally prove its presence.
a) Production of ammonia.
Heat a mixture of equal volume portions of solid ammonium chloride and calcium hydroxide powder in a test tube with a gas outlet tube. In this case, ammonia will be released, which must be collected in another dry test tube located with a hole ............ ( Why?).
Write the reaction equation for the production of ammonia.
…………………………………………………..
b) Determination of ammonia.
Can be identified by smell………… (name of substance), as well as by changes in the color of litmus or phenolphthalein. When ammonia is dissolved in water, ...... is formed. (name of base), so the litmus test...... (specify color), and colorless phenolphthalein becomes …………. (specify color).
Instead of dots, insert words according to their meaning. Write the reaction equation.
…………………………………………………..
* Ammonia, an aqueous solution of ammonia, smells like ammonia. – Note ed.
Task 2
Obtain copper nitrate in two different ways, having the following substances available: concentrated nitric acid, copper filings, copper(II) sulfate, sodium hydroxide. Write equations for chemical reactions in molecular form and note the changes. In method 1, for a redox reaction, write electron balance equations, determine the oxidizing agent and the reducing agent. In method 2, write abbreviated ionic reaction equations.
1st s p o s o b. Copper + nitric acid. Lightly heat the contents of the test tube. The colorless solution becomes….. (specify color), because is formed….. (name of substance); gas is released……..colored with an unpleasant odor, this is……. (name of substance).
2nd s p o s o b. When copper(II) sulfate reacts with sodium hydroxide, a precipitate of ..... color is obtained, this is ...... (name of substance). Add nitric acid to it until the precipitate is completely dissolved......... (name of sediment). A clear blue solution is formed...... (name of salt).
Task 3
Prove experimentally that ammonium sulfate contains NH 4 + and SO 2- 4 ions. Note the observations and write molecular and abbreviated ionic equations for the reactions.
Task 4
How to experimentally determine the presence of solutions of sodium orthophosphate, sodium chloride, sodium nitrate in test tubes No. 1, No. 2, No. 3? Note the observations and write molecular and abbreviated ionic equations for the reactions.
Task 5
Having the following substances: nitric acid, copper shavings or wire, universal indicator paper or methyl orange, prove experimentally the composition of nitric acid. Write the equation for the dissociation of nitric acid; molecular equation for the reaction of copper with concentrated nitric acid and electron balance equations, identify the oxidizing agent and the reducing agent.
Task 6
Prepare a solution of copper nitrate in different ways, using the substances: nitric acid, copper oxide, basic copper carbonate or hydroxycopper(II) carbonate. Write molecular, complete and abbreviated ionic equations for chemical reactions. Note signs of chemical reactions.
Benchmark tests
1. Give the reaction equation where a yellow precipitate forms.
2. The ionic equation of the reaction in which the white cheesy precipitate is formed is:
3. To prove the presence of nitrate ion in nitrates, you need to take:
a) hydrochloric acid and zinc;
b) sulfuric acid and sodium chloride;
c) sulfuric acid and copper.
4. The reagent for chloride ion is:
a) copper and sulfuric acid;
b) silver nitrate;
c) barium chloride.
5. In the reaction equation, the diagram of which
HNO 3 + Cu -> Cu(NO 3) 2 + NO 2 + H 2 O,
Before the oxidizing agent you need to put the coefficient:
a) 2; b) 4; c) 6.
6. Basic and acid salts correspond to the pairs:
a) Cu(OH) 2, Mg(HCO 3) 2;
b) Cu(NO 3) 2, HNO 3;
c) 2 CO 3, Ca(HCO 3) 2.
|
Answers. 1 -A; 2 -b; 3 -V; 4 -b; 5 -b; 6 -V. |
Determination of mineral fertilizers
The methodological development of this practical work consists of three parts: theory, workshop, control. The theoretical part provides general information on the qualitative determination of cations and anions included in mineral fertilizers. The workshop provides examples of seven mineral fertilizers with a description of them characteristic features, and also the equations of qualitative reactions are given. In the text, instead of dots and question marks, you need to insert answers that are appropriate in meaning. To complete practical work at the teacher's discretion, it is enough to take four fertilizers. Testing students' knowledge consists of test tasks to determine fertilizer formulas, which are given in this practical work.
Theory
1. The reagent for chloride ion is silver nitrate. The reaction proceeds with the formation of a white cheesy precipitate:
Ag + + Cl – = AgCl.
2. Ammonium ion can be detected using alkali. When a solution of ammonium salt is heated with an alkali solution, ammonia is released, which has a sharp characteristic odor:
NH + 4 + OH – = NH 3 + H 2 O.
You can also use red litmus paper moistened with water, a universal indicator or phenolphthalein strip of paper to determine the ammonium ion. The piece of paper must be held over the vapors released from the test tube. Red litmus turns blue, the universal indicator turns purple, and phenolphthalein turns crimson.
3. To determine nitrate ions, copper shavings or pieces are added to the salt solution, then concentrated sulfuric acid is added and heated. After some time, a brown gas with an unpleasant odor begins to be released. The release of brown NO2 gas indicates the presence of ions.
For example:
NaNO 3 + H 2 SO 4 NaHSO 4 + HNO 3,
4HNO 3 + Cu = Cu(NO 3) 2 + 2NO 2 + 2H 2 O.
4. The reagent for phosphate ion is silver nitrate. When it is added to a phosphate solution, a yellow precipitate of silver phosphate precipitates:
3Ag + + PO 3- 4 = Ag 3 PO 4.
5. The reagent for sulfate ion is barium chloride. A white milky precipitate of barium sulfate appears, insoluble in acetic acid:
Ba 2+ + SO 2- 4 = BaSO 4 .
Workshop
1. Sylvinite (NaCl KCl), pink crystals, good solubility in water. The flame turns yellow. When viewing the flame through blue glass, a violet color is noticeable. WITH …….. (name of reagent) gives a white precipitate...... (name of salt).
KCl + ? -> KNO 3 + AgCl.
2. Ammonium nitrate NH 4 NO 3, or…….. (name of fertilizer), white crystals, highly soluble in water. Brown gas is released with sulfuric acid and copper... (name of substance). With solution……. (name of reagent) When heated, the smell of ammonia is felt, its vapor turns red litmus into....... color.
NH 4 NO 3 + H 2 SO 4 NH 4 HSO 4 + HNO 3,
HNO 3 + Cu -> Cu(NO 3) 2 + ? + ? .
NH 4 NO 3 + ? -> NH 3 + H 2 O + NaNO 3.
3. Potassium nitrate (KNO 3), or…… (name of fertilizer), with H 2 SO 4 and ……… (name of substance) produces brown gas. The flame turns purple.
KNO 3 + H 2 SO 4 KHSO 4 + HNO 3,
4HNO 3 + ? -> Cu(NO 3) 2 + ? + 2H 2 O.
4. Ammonium chloride NH 4 Cl with solution……. (name of reagent) When heated, it forms ammonia, its vapors turn red litmus blue. WITH …… (name of the reagent anion) silver gives a white cheesy precipitate...... (name of sediment).
NH 4 Cl + ? = NH 4 NO 3 + AgCl,
NH 4 Cl + ? = NH 3 + H 2 O + NaCl.
5. When heated, ammonium sulfate (NH 4) 2 SO 4 with an alkali solution forms ammonia; its vapor turns red litmus blue. WITH …….. (name of reagent) gives a white milky sediment......... (name of sediment).
(NH 4) 2 SO 4 + 2NaOH = 2NH 3 + 2H 2 O + ? ,
(NH 4) 2 SO 4 + ? -> NH 4 Cl + ? .
6. Sodium nitrate NaNO 3, or…… (name of fertilizer), white crystals, good solubility in water, produces a brown gas with H 2 SO 4 and Cu. The flame turns yellow.
NaNO 3 + H 2 SO 4 NaHSO 4 + ? ,
Cu -> Cu(NO 3) 2 + ? + 2H 2 O.
7. Calcium dihydrogen phosphate Ca(H 2 PO 4) 2, or…… (name of fertilizer), gray fine-grained powder or granules, poorly soluble in water, with ..... (name of reagent) gives ….. (specify color) precipitate ……… (name of substance) AgH 2 PO 4.
Ca(H 2 PO 4) 2 + ? -> 2AgH 2 PO 4 + Ca(NO 3) 2.
Control (test)
1. Pink crystals, highly soluble in water, color the flame yellow; when interacting with AgNO 3, a white precipitate forms - this is:
a) Ca(H 2 PO 4) 2; b) NaCl KCl;
c) KNO 3; d) NH 4 Cl.
2. The crystals are highly soluble in water; in reaction with H 2 SO 4 and copper, a brown gas is released; with an alkali solution, when heated, it produces ammonia, the vapors of which turn red litmus blue - this is:
a) NaNO 3; b) (NH 4) 2 SO 4;
c) NH 4 NO 3; d) KNO 3.
3. Light crystals, highly soluble in water; upon interaction with H 2 SO 4 and Cu, brown gas is released; the flame turns purple - this is:
a) KNO 3; b) NH 4 H 2 PO 4;
c) Ca(H 2 PO 4) 2 CaSO 4; d) NH 4 NO 3.
4. The crystals are highly soluble in water; with silver nitrate it gives a white precipitate, with alkali when heated it gives ammonia, the vapors of which turn red litmus blue - this is:
a) (NH 4) 2 SO 4; b) NH 4 H 2 PO 4;
c) NaCl KCl; d) NH 4 Cl.
5. Light crystals, highly soluble in water; with BaCl 2 it gives a white milky precipitate, with alkali it gives ammonia, the vapors of which turn red litmus blue - this is:
c) NH 4 Cl; d) NH 4 H 2 PO 4.
6. Light crystals, highly soluble in water; when interacting with H 2 SO 4 and Cu, it produces a brown gas, the flame turns yellow - this is:
a) NH 4 NO 3; b) (NH 4) 2 SO 4;
c) KNO 3; d) NaNO 3.
7. Gray fine-grained powder or granules, solubility in water is poor, with a solution of silver nitrate it gives a yellow precipitate - this is:
a) (NH 4) 2 SO 4; b) NaCl KCl;
c) Ca(H 2 PO 4) 2; d) KNO 3.
| Answers. 1 -b; 2 -V; 3 -A; 4 -G; 5 -b; 6 -G; 7 -V. |
Let's imagine this situation:
You are working in a laboratory and have decided to conduct an experiment. To do this, you opened the cabinet with reagents and suddenly saw the following picture on one of the shelves. Two jars of reagents had their labels peeled off and safely remained lying nearby. At the same time, it is no longer possible to determine exactly which jar corresponds to which label, and the external signs of the substances by which they could be distinguished are the same.
In this case, the problem can be solved using the so-called qualitative reactions.
Qualitative reactions These are reactions that make it possible to distinguish one substance from another, as well as to find out the qualitative composition of unknown substances.
For example, it is known that cations of some metals, when their salts are added to the burner flame, color it a certain color:
This method can only work if the substances being distinguished change the color of the flame differently, or one of them does not change color at all.
But, let’s say, as luck would have it, the substances being determined do not color the flame, or color it the same color.
In these cases, it will be necessary to distinguish substances using other reagents.
In what case can we distinguish one substance from another using any reagent?
There are two options:
- One substance reacts with the added reagent, but the second does not. In this case, it must be clearly visible that the reaction of one of the starting substances with the added reagent actually took place, that is, some external sign of it is observed - a precipitate formed, a gas was released, a color change occurred, etc.
For example, it is impossible to distinguish water from a solution of sodium hydroxide using hydrochloric acid, despite the fact that alkalis react well with acids:
NaOH + HCl = NaCl + H2O
This is due to the lack of any external signs reactions. A clear, colorless solution of hydrochloric acid when mixed with a colorless hydroxide solution forms the same clear solution:
But on the other hand, you can distinguish water from an aqueous solution of alkali, for example, using a solution of magnesium chloride - in this reaction a white precipitate forms:
2NaOH + MgCl 2 = Mg(OH) 2 ↓+ 2NaCl
2) substances can also be distinguished from each other if they both react with the added reagent, but do so in different ways.
For example, you can distinguish a sodium carbonate solution from a silver nitrate solution using a hydrochloric acid solution.
Hydrochloric acid reacts with sodium carbonate to release a colorless, odorless gas - carbon dioxide (CO 2):
2HCl + Na 2 CO 3 = 2NaCl + H 2 O + CO 2
and with silver nitrate to form a white cheesy precipitate AgCl
HCl + AgNO 3 = HNO 3 + AgCl↓
The tables below present various options detection of specific ions:
Qualitative reactions to cations
| Cation | Reagent | Sign of reaction |
| Ba 2+ | SO 4 2- | Ba 2+ + SO 4 2- = BaSO 4 ↓ |
| Cu 2+ | 1) Precipitation of blue color: Cu 2+ + 2OH − = Cu(OH) 2 ↓ 2) Black precipitate: Cu 2+ + S 2- = CuS↓ |
|
| Pb 2+ | S 2- | Black precipitate: Pb 2+ + S 2- = PbS↓ |
| Ag+ | Cl − | Precipitation of a white precipitate, insoluble in HNO 3, but soluble in ammonia NH 3 ·H 2 O: Ag + + Cl − → AgCl↓ |
| Fe 2+ | 2) Potassium hexacyanoferrate (III) (red blood salt) K 3 | 1) Precipitation of a white precipitate that turns green in air: Fe 2+ + 2OH − = Fe(OH) 2 ↓ 2) Precipitation of a blue precipitate (Turnboole blue): K + + Fe 2+ + 3- = KFe↓ |
| Fe 3+ | 2) Potassium hexacyanoferrate (II) (yellow blood salt) K 4 3) Rodanide ion SCN − | 1) Brown precipitate: Fe 3+ + 3OH − = Fe(OH) 3 ↓ 2) Precipitation of blue precipitate (Prussian blue): K + + Fe 3+ + 4- = KFe↓ 3) The appearance of intense red (blood red) coloring: Fe 3+ + 3SCN − = Fe(SCN) 3 |
| Al 3+ | Alkali (amphoteric properties of hydroxide) | Precipitation of a white precipitate of aluminum hydroxide when adding a small amount of alkali: OH − + Al 3+ = Al(OH) 3 and its dissolution upon further pouring: Al(OH) 3 + NaOH = Na |
| NH4+ | OH − , heating | Emission of gas with a pungent odor: NH 4 + + OH − = NH 3 + H 2 O Blue turning of wet litmus paper |
| H+ (acidic environment) | Indicators: − litmus − methyl orange | Red staining |
Qualitative reactions to anions
| Anion | Impact or reagent | Sign of reaction. Reaction equation |
| SO 4 2- | Ba 2+ | Precipitation of a white precipitate, insoluble in acids: Ba 2+ + SO 4 2- = BaSO 4 ↓ |
| NO 3 − | 1) Add H 2 SO 4 (conc.) and Cu, heat 2) Mixture of H 2 SO 4 + FeSO 4 | 1) Formation of a blue solution containing Cu 2+ ions, release of brown gas (NO 2) 2) The appearance of color of nitroso-iron (II) sulfate 2+. Color ranges from violet to brown (brown ring reaction) |
| PO 4 3- | Ag+ | Precipitation of a light yellow precipitate in a neutral environment: 3Ag + + PO 4 3- = Ag 3 PO 4 ↓ |
| CrO 4 2- | Ba 2+ | Formation of a yellow precipitate, insoluble in acetic acid, but soluble in HCl: Ba 2+ + CrO 4 2- = BaCrO 4 ↓ |
| S 2- | Pb 2+ | Black precipitate: Pb 2+ + S 2- = PbS↓ |
| CO 3 2- | 1) Precipitation of a white precipitate, soluble in acids: Ca 2+ + CO 3 2- = CaCO 3 ↓ 2) The release of colorless gas (“boiling”), causing cloudiness of lime water: CO 3 2- + 2H + = CO 2 + H 2 O |
|
| CO2 | Lime water Ca(OH) 2 | Precipitation of a white precipitate and its dissolution with further passage of CO 2: Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2 |
| SO 3 2- | H+ | Emission of SO 2 gas with a characteristic pungent odor (SO 2): 2H + + SO 3 2- = H 2 O + SO 2 |
| F − | Ca2+ | White precipitate: Ca 2+ + 2F − = CaF 2 ↓ |
| Cl − | Ag+ | Precipitation of a white cheesy precipitate, insoluble in HNO 3, but soluble in NH 3 ·H 2 O (conc.): Ag + + Cl − = AgCl↓ AgCl + 2(NH 3 ·H 2 O) = ) |
Harmful working conditions Documents confirming work in hazardous working conditions
Topic in German “Umwelt” (Environment) Message in German on the topic of nature
How do you understand the main idea of the excerpt from the poem N