A certain amount of zinc sulfide was divided into two parts, one of them is the treatment. The tasks of the exam: a thought experiment
1) Silicon was burned in a chlorine atmosphere. The resulting chloride was treated with water. The precipitate that formed was calcined. Then it was fused with calcium phosphate and coal. Make the equations for the four reactions described.
2) The gas obtained by treating calcium nitride with water was passed over a red-hot powder of copper (II) oxide. The resulting solid was dissolved in concentrated nitric acid, the solution was evaporated, and the resulting solid residue was calcined. Make the equations for the four reactions described.
3) Some amount of iron (II) sulfide was divided into two parts. One of them was treated with hydrochloric acid, and the other was fired in air. During the interaction of the released gases, a simple yellow substance was formed. The resulting substance was heated with concentrated nitric acid, while a brown gas was evolved. Write the equations for the four reactions described.
4) When aluminum oxide interacts with nitric acid, a salt is formed. The salt was dried and calcined. The solid residue formed during calcination was subjected to electrolysis in molten cryolite. The metal obtained by electrolysis was heated with a concentrated solution containing potassium nitrate and potassium hydroxide, while a gas with a pungent odor was released. Write the equations for the four reactions described.
5) Chromium (VI) oxide reacted with potassium hydroxide. The resulting substance was treated with sulfuric acid, and the orange salt was isolated from the resulting solution. This salt was treated with hydrobromic acid. The resulting simple substance reacted with hydrogen sulfide. Write the equations for the four reactions described.
6) Magnesium powder was heated under nitrogen atmosphere. When the resulting substance interacted with water, gas was released. The gas was passed through an aqueous solution of chromium (III) sulfate, resulting in the formation of a gray precipitate. The precipitate was separated and treated under heating with a solution containing hydrogen peroxide and potassium hydroxide. Write the equations for the four reactions described.
7) Ammonia was passed through hydrobromic acid. Silver nitrate solution was added to the resulting solution. The precipitate that formed was separated and heated with zinc powder. The metal formed during the reaction was acted upon with a concentrated solution of sulfuric acid, and gas with a pungent odor was released. Write the equations for the four reactions described.
8) Potassium chlorate was heated in the presence of a catalyst, while a colorless gas was evolved. By burning iron in an atmosphere of this gas, iron scale was obtained. It was dissolved in an excess of hydrochloric acid. To the resulting solution was added a solution containing sodium dichromate and hydrochloric acid. Write the equations for the four reactions described.
9) Sodium was heated in a hydrogen atmosphere. On adding water to the obtained substance, gas evolution and the formation of a clear solution were observed. A brown gas was passed through this solution, which was obtained as a result of the interaction of copper with a concentrated solution of nitric acid. Write the equations for the four reactions described.
10) Aluminum reacted with sodium hydroxide solution. The evolved gas was passed over a heated copper (II) oxide powder. The resulting simple substance was dissolved by heating in concentrated sulfuric acid. The resulting salt was isolated and added to the potassium iodide solution. Write the equations for the four reactions described.
11) Conducted electrolysis of sodium chloride solution. Iron (III) chloride was added to the resulting solution. The formed precipitate was filtered off and calcined. The solid residue was dissolved in hydroiodic acid. Write the equations for the four reactions described.
12) Aluminum powder was added to the sodium hydroxide solution. An excess of carbon dioxide was passed through the solution of the obtained substance. The formed precipitate was separated and calcined. The resulting product was fused with sodium carbonate. Write the equations for the four reactions described.
1) Copper nitrate was calcined, the resulting solid precipitate was dissolved in sulfuric acid. Hydrogen sulfide was passed through the solution, the resulting black precipitate was calcined, and the solid residue was dissolved by heating in concentrated nitric acid.
2) Calcium phosphate was fused with coal and sand, then the resulting simple substance was burned in an excess of oxygen, the combustion product was dissolved in an excess of sodium hydroxide. A solution of barium chloride was added to the resulting solution. The resulting precipitate was treated with an excess of phosphoric acid.
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Ca 3 (PO 4) 2 → P → P 2 O 5 → Na 3 PO 4 → Ba 3 (PO 4) 2 → BaHPO 4 or Ba (H 2 PO 4) 2 Ca 3 (PO 4) 2 + 5C + 3SiO 2 → 3CaSiO 3 + 2P + 5CO |
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3) Copper was dissolved in concentrated nitric acid, the resulting gas was mixed with oxygen and dissolved in water. Zinc oxide was dissolved in the resulting solution, then a large excess of sodium hydroxide solution was added to the solution.
4) Dry sodium chloride was acted upon with concentrated sulfuric acid under low heating, the resulting gas was passed into a barium hydroxide solution. Potassium sulfate solution was added to the resulting solution. The resulting precipitate was fused with coal. The resulting material was treated with hydrochloric acid.
5) A weighed portion of aluminum sulfide was treated with hydrochloric acid. In this case, gas was released and a colorless solution was formed. An ammonia solution was added to the resulting solution, and the gas was passed through a lead nitrate solution. The resulting precipitate was treated with a hydrogen peroxide solution.
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Al (OH) 3 ← AlCl 3 ← Al 2 S 3 → H 2 S → PbS → PbSO 4 Al 2 S 3 + 6HCl → 3H 2 S + 2AlCl 3 |
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6) Aluminum powder was mixed with sulfur powder, the mixture was heated, the resulting substance was treated with water, while gas was released and a precipitate was formed, to which an excess of potassium hydroxide solution was added until complete dissolution. This solution was evaporated and calcined. An excess of hydrochloric acid solution was added to the resulting solid.
7) A solution of potassium iodide was treated with a solution of chlorine. The resulting precipitate was treated with sodium sulfite solution. To the resulting solution, a solution of barium chloride was added first, and after separation of the precipitate, a solution of silver nitrate was added.
8) Gray-green powder of chromium (III) oxide was fused with an excess of alkali, the resulting substance was dissolved in water, and a dark green solution was obtained. Hydrogen peroxide was added to the resulting alkaline solution. The result is a yellow solution, which becomes orange when added with sulfuric acid. When hydrogen sulfide is passed through the resulting acidified orange solution, it becomes cloudy and turns green again.
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Cr 2 O 3 → KCrO 2 → K → K 2 CrO 4 → K 2 Cr 2 O 7 → Cr 2 (SO 4) 3 Cr 2 O 3 + 2KOH → 2KCrO 2 + H 2 O |
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9) Aluminum was dissolved in a concentrated solution of potassium hydroxide. Carbon dioxide was passed through the resulting solution until the precipitation ceased. The precipitate was filtered off and calcined. The resulting solid residue was fused with sodium carbonate.
10) Silicon was dissolved in a concentrated solution of potassium hydroxide. An excess of hydrochloric acid was added to the resulting solution. The cloudy solution was heated. The separated precipitate was filtered off and calcined with calcium carbonate. Write the equations for the described reactions.
11) Copper (II) oxide was heated in a stream of carbon monoxide. The resulting substance was burned in a chlorine atmosphere. The reaction product was dissolved in water. The resulting solution was divided into two parts. Potassium iodide solution was added to one part, and silver nitrate solution to the second. In both cases, the formation of a precipitate was observed. Write the equations for the four reactions described.
12) Copper nitrate was calcined, the resulting solid was dissolved in dilute sulfuric acid. The resulting salt solution was subjected to electrolysis. The substance released at the cathode was dissolved in concentrated nitric acid. Dissolution proceeded with the evolution of brown gas. Write the equations for the four reactions described.
13) Iron was burned in a chlorine atmosphere. The resulting material was treated with an excess of sodium hydroxide solution. A brown precipitate formed, which was filtered off and calcined. The residue after calcination was dissolved in hydroiodic acid. Write the equations for the four reactions described.
14) Powder of metallic aluminum was mixed with solid iodine and a few drops of water were added. Sodium hydroxide solution was added to the resulting salt until a precipitate formed. The resulting precipitate was dissolved in hydrochloric acid. Upon subsequent addition of the sodium carbonate solution, precipitation was again observed. Write the equations for the four reactions described.
15) As a result of incomplete combustion of coal, a gas was obtained, in a stream of which iron (III) oxide was heated. The resulting material was dissolved in hot concentrated sulfuric acid. The resulting salt solution was subjected to electrolysis. Write the equations for the four reactions described.
16) Some zinc sulfide was divided into two parts. One of them was treated with nitric acid, and the other was fired in air. A simple substance was formed during the interaction of the evolved gases. This substance was heated with concentrated nitric acid, and a brown gas was evolved. Write the equations for the four reactions described.
17) Potassium chlorate was heated in the presence of a catalyst, while a colorless gas was evolved. By burning iron in an atmosphere of this gas, iron scale was obtained. It was dissolved in an excess of hydrochloric acid. To the resulting solution was added a solution containing sodium dichromate and hydrochloric acid.
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1) 2КClО 3 → 2КСl + 3О 2 2) ЗFe + 2O 2 → Fe 3 O 4 3) Fe 3 O 4 + 8HCI → FeCl 2 + 2FeCl 3 + 4H 2 O 4) 6 FeCl 2 + Na 2 Cr 2 O 7 + 14 НСІ → 6 FeCl 3 + 2 CrCl 3 + 2NaCl + 7Н 2 О 18) Iron was burned in chlorine. The resulting salt was added to the sodium carbonate solution, and a brown precipitate formed. This precipitate was filtered off and calcined. The resulting substance was dissolved in hydroiodic acid. Write the equations for the four reactions described. 1) 2Fe + 3Cl 2 → 2FeCl 3 2) 2FeCl 3 + 3Na 2 CO 3 → 2Fe (OH) 3 + 6NaCl + 3CO 2 3) 2Fe (OH) 3 Fe 2 O 3 + 3H 2 O 4) Fe 2 O 3 + 6HI → 2FeI 2 + I 2 + 3H 2 O |
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19) A solution of potassium iodide was treated with an excess of chlorine water, while the formation of a precipitate was observed first, and then its complete dissolution. The resulting iodine-containing acid was isolated from the solution, dried and heated carefully. The resulting oxide reacted with carbon monoxide. Write down the equations of the described reactions.
20) Powder of chromium (III) sulfide was dissolved in sulfuric acid. In this case, gas was released and a colored solution was formed. An excess of ammonia solution was added to the resulting solution, and the gas was passed through lead nitrate. The resulting black precipitate turned white after treatment with hydrogen peroxide. Write down the equations of the described reactions.
21) Aluminum powder was heated with sulfur powder, the resulting substance was treated with water. The precipitate that formed was treated with an excess of concentrated potassium hydroxide solution until it was completely dissolved. To the resulting solution was added a solution of aluminum chloride and again observed the formation of a white precipitate. Write down the equations of the described reactions.
22) Potassium nitrate was heated with powdered lead until the reaction was terminated. The product mixture was treated with water, and then the resulting solution was filtered. The filtrate was acidified with sulfuric acid and treated with potassium iodide. The separated simple substance was heated with concentrated nitric acid. In the atmosphere of the resulting brown gas, red phosphorus was burned. Write down the equations of the described reactions.
23) Copper was dissolved in dilute nitric acid. An excess of ammonia solution was added to the resulting solution, observing first the formation of a precipitate, and then its complete dissolution with the formation of a dark blue solution. The resulting solution was treated with sulfuric acid until the characteristic blue color of copper salts appeared. Write down the equations of the described reactions.
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1) 3Cu + 8HNO 3 → 3Cu (NO 3) 2 + 2NO + 4H 2 O 2) Cu (NO 3) 2 + 2NH 3 H 2 O → Cu (OH) 2 + 2NH 4 NO 3 3) Cu (OH) 2 + 4NH 3 H 2 O → (OH) 2 + 4H 2 O 4) (OH) 2 + 3H 2 SO 4 → CuSO 4 +2 (NH 4) 2 SO 4 + 2H 2 O |
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24) Magnesium was dissolved in dilute nitric acid, and no gas evolution was observed. The resulting solution was treated with an excess of potassium hydroxide solution with heating. The gas released during this process was burned in oxygen. Write down the equations of the described reactions.
25) A mixture of potassium nitrite and ammonium chloride powders was dissolved in water and the solution was gently heated. The released gas reacted with magnesium. The reaction product was added to an excess of hydrochloric acid solution, and no gas evolution was observed. The obtained magnesium salt in solution was treated with sodium carbonate. Write down the equations of the described reactions.
26) Aluminum oxide was fused with sodium hydroxide. The reaction product was introduced into the ammonium chloride solution. The released gas with a pungent odor is absorbed by the sulfuric acid. The resulting middle salt was calcined. Write down the equations of the described reactions.
27) Chlorine has reacted with hot potassium hydroxide solution. When the solution was cooled, crystals of berthollet's salt precipitated. The crystals obtained were introduced into a hydrochloric acid solution. The resulting simple substance reacted with metallic iron. The reaction product was heated with a new weight of iron. Write down the equations of the described reactions.
28) Copper was dissolved in concentrated nitric acid. An excess of ammonia solution was added to the resulting solution, observing first the formation of a precipitate, and then its complete dissolution. The resulting solution was treated with an excess of hydrochloric acid. Write down the equations of the described reactions.
29) Iron was dissolved in hot concentrated sulfuric acid. The resulting salt was treated with an excess of sodium hydroxide solution. The resulting brown precipitate was filtered off and calcined. The resulting substance was fused with iron. Write the equations for the four reactions described.
30) As a result of incomplete combustion of coal, a gas was obtained, in the current of which iron oxide (III) was heated. The resulting material was dissolved in hot concentrated sulfuric acid. The resulting salt solution was treated with an excess of potassium sulfide solution.
31) Some zinc sulfide was divided into two parts. One of them was treated with hydrochloric acid, and the other was fired in air. A simple substance was formed during the interaction of the evolved gases. This substance was heated with concentrated nitric acid, and a brown gas was released.
32) Sulfur was fused with iron. The reaction product was treated with hydrochloric acid. The gas released during this was burned in an excess of oxygen. The combustion products were absorbed in an aqueous solution of iron sulfate (III).
№37 exam
The interaction of aluminum oxide with nitric acid formed a salt. The salt was dried and calcined. The solid residue formed during calcination was subjected to electrolysis in molten cryolite. The metal obtained by electrolysis was heated with a concentrated solution containing potassium nitrate and potassium hydroxide, while a gas with a pungent odor was released. Write the equations for the described reactions.
Potassium chlorate was heated in the presence of a catalyst. The resulting salt was dissolved in water and subjected to electrolysis. A yellow-green gas evolved at the anode, which was passed through a sodium iodide solution. The simple substance formed as a result of this reaction reacted by heating with a solution of potassium hydroxide. Write the equations for the described reactions.
An iron plate was placed in the copper (II) sulfate solution. At the end of the reaction, the plate was removed, and a solution of barium nitrate was added dropwise to the resulting greenish solution until the formation of a precipitate ceased. The precipitate was filtered off, the solution was evaporated, and the remaining dry salt was calcined in air. This formed a brown solid, which was treated with concentrated hydroiodic acid. Write the equations for the described reactions.
The salt obtained by dissolving iron in hot concentrated sulfuric acid was treated with a sodium hydroxide solution. The resulting brown precipitate was filtered off and calcined. The resulting substance was fused with iron. Write the equations for the described reactions.
Manganese (IV) oxide reacted on heating with concentrated hydrochloric acid. The released gas was passed through a sodium hydroxide solution in the cold. The resulting solution was divided into two parts. Silver nitrate solution was added to one part of the solution, resulting in a white precipitate. Potassium iodide solution was added to the other part of the solution. As a result, a dark brown precipitate fell out. Write the equations for the 4 described reactions.
Iron powder was dissolved in hydrochloric acid. Chlorine was passed through the resulting solution, as a result of which the solution acquired a yellowish color. An ammonium sulfide solution was added to this solution, resulting in a precipitate. The resulting precipitate was acted upon with a solution of sulfuric acid, and part of the precipitate was dissolved. The insoluble part was yellow. Write the equations for the described reactions.
Alkalis were added to the aluminum-copper alloy. Carbon dioxide was passed through the resulting solution until the precipitation ceased. The precipitate was filtered off and calcined, and the solid residue was fused with sodium carbonate. Write the equations for the described reactions.
Zinc chloride was dissolved in excess alkali. Carbon dioxide was passed through the resulting solution until the precipitation ceased. The precipitate was filtered off and calcined, and the solid residue was calcined with charcoal. Write the equations for the described reactions.
A solution of the original salt was given, to which sodium hydroxide was added and heated, a gas with an irritating odor was released and a salt solution was formed, upon adding a dilute solution of hydrochloric acid to which a gas with the smell of rotten eggs was released. If a solution of lead nitrate is added to the solution of the initial salt, two salts are formed: one in the form of a black precipitate, the other salt soluble in water. After removing the precipitate and calcining the filtrate, a mixture of two gases is formed, one of which is water vapor. Write the equations for the described reactions.
The iron was calcined in air. The resulting compound, in which iron is in two oxidation states, was dissolved in a strictly necessary amount of concentrated sulfuric acid. An iron plate was lowered into the solution and held until its mass ceased to decrease. Then alkali was added to the solution and a precipitate formed. Write the equations for the described reactions.
Some of the iron (II) sulfide was divided into two parts. Out of them were treated with hydrochloric acid, and the other was fired in air. The interaction of the evolved gases formed a simple yellow substance. The resulting substance was heated with concentrated sulfuric acid, while a brown gas was evolved. Write the equations for the described reactions.
Silicon was burned in a chlorine atmosphere. The resulting chloride was treated with water. The precipitate that formed was calcined. Then fused with calcium phosphate and coal. Make the equations for the reactions described.
The iron was burned in chlorine. The resulting salt was added to a sodium carbonate solution, and a brown precipitate formed, which was filtered off and calcined. The resulting substance was dissolved in hydroiodic acid. Write the equations described reactions.
3) Copper was dissolved in concentrated nitric acid, the resulting gas was mixed with oxygen and dissolved in water. Zinc oxide was dissolved in the resulting solution, then a large excess of sodium hydroxide solution was added to the solution.Make the equations for the four reactions described.
4) Dry sodium chloride was acted upon with concentrated sulfuric acid under low heating, the resulting gas was passed into a barium hydroxide solution. Potassium sulfate solution was added to the resulting solution. The resulting precipitate was fused with coal. The resulting material was treated with hydrochloric acid. Make the equations for the four reactions described.
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6) Silicon was burned in a chlorine atmosphere. The resulting chloride was treated with water. The precipitate that formed was calcined. Then it was fused with calcium phosphate and coal. Write the equations for the four reactions described.
7) The gas obtained by treating calcium nitride with water was passed over a red-hot powder of copper (II) oxide. The resulting solid was dissolved in concentrated nitric acid, the solution was evaporated, and the resulting solid was calcined. Make the equations for the four reactions described.
8) A certain amount of iron (II) sulfide was divided into two parts. One of them was treated with hydrochloric acid, and the other was fired in air. The interaction of the evolved gases formed a simple yellow substance. The resulting substance was heated with concentrated nitric acid, while a brown gas was evolved.
9) When aluminum oxide interacts with nitric acid, a salt is formed. The salt was dried and calcined. The solid residue formed during calcination was subjected to electrolysis in molten cryolite. The metal obtained by electrolysis was heated with a concentrated solution containing potassium nitrate and potassium hydroxide, while a gas with a pungent odor was released.Write the equations for the four reactions described.
10) Chromium (IV) oxide reacted with potassium hydroxide. The resulting substance was treated with sulfuric acid, and the orange salt was isolated from the resulting solution. This salt was treated with hydrobromic acid. The resulting simple substance reacted with hydrogen sulfide.Write the equations for the four reactions described.
11) Magnesium powder was heated under nitrogen atmosphere. When the resulting substance interacted with water, gas was released. The gas was passed through an aqueous solution of chromium (III) sulfate, resulting in the formation of a gray precipitate. The precipitate was separated and treated under heating with a solution containing hydrogen peroxide and potassium hydroxide.Write the equations for the four reactions described.
12) Ammonia was passed through hydrobromic acid. Silver nitrate solution was added to the resulting solution. The precipitate that formed was separated and heated with zinc powder. The metal formed during the reaction was acted upon with a concentrated solution of sulfuric acid, and gas with a pungent odor was released.Write the equations for the four reactions described.
13) Potassium chlorate was heated in the presence of a catalyst, while a colorless gas was evolved. By burning iron in an atmosphere of this gas, iron scale was obtained. It was dissolved in an excess of hydrochloric acid. To the resulting solution was added a solution containing sodium dichromate and hydrochloric acid.Write the equations for the four reactions described.
14) Sodium was heated in a hydrogen atmosphere. On adding water to the obtained substance, gas evolution and the formation of a clear solution were observed. A brown gas was passed through this solution, which was obtained as a result of the interaction of copper with a concentrated solution of nitric acid. Write the equations for the four reactions described.
15) Aluminum reacted with sodium hydroxide solution. The evolved gas was passed over a heated copper (II) oxide powder. The resultingthe simple substance was dissolved by heating in concentrated sulfuric acid. The resulting salt was isolated and added to the potassium iodide solution. Make the equations for the four reactions described.
16) Conducted electrolysis of sodium chloride solution. An iron (III) chloride solution was added to the resulting solution. The formed precipitate was filtered off and calcined. The solid residue was dissolved in hydroiodic acid.Write the equations for the four reactions described.
17) Aluminum powder was added to the sodium hydroxide solution. An excess of carbon dioxide was passed through the solution of the obtained substance. The formed precipitate was separated and calcined. The resulting product was fused with sodium carbonate.Write the equations for the four reactions described.
Task number 1
The sodium was heated in a hydrogen atmosphere. On adding water to the obtained substance, gas evolution and the formation of a clear solution were observed. A brown gas was passed through this solution, which was obtained as a result of the interaction of copper with a concentrated solution of nitric acid. Write the equations for the four reactions described.
1) When sodium is heated in a hydrogen atmosphere (T = 250-400 o C), sodium hydride is formed):
2Na + H 2 = 2NaH
2) When water is added to sodium hydride, alkali NaOH is formed, and hydrogen is released:
NaH + H 2 O = NaOH + H 2
3) When copper interacts with a concentrated solution of nitric acid, brown gas is released - NO 2:
Cu + 4HNO 3 (conc.) = Cu (NO 3) 2 + 2NO 2 + 2H 2 O
4) When the brown gas NO 2 is passed through an alkali solution, a disproportionation reaction occurs - nitrogen N +4 is simultaneously oxidized and reduced to N +5 and N +3:
2NaOH + 2NO 2 = NaNO 3 + NaNO 2 + H 2 O
(disproportionation reaction 2N +4 → N +5 + N +3).
Task number 2
Iron scale was dissolved in concentrated nitric acid. Sodium hydroxide solution was added to the resulting solution. The separated precipitate was separated and calcined. The resulting solid residue was fused with iron. Write the equations for the four reactions described.
The formula for iron scale is Fe 3 O 4.
When iron scale interacts with concentrated nitric acid, iron nitrate is formed and nitrogen oxide NO 2 is released:
Fe 3 O 4 + 10HNO 3 (conc.) → 3Fe (NO 3) 3 + NO 2 + 5H 2 O
When iron nitrate interacts with sodium hydroxide, a precipitate is formed - iron (III) hydroxide:
Fe (NO 3) 3 + 3NaOH → Fe (OH) 3 ↓ + 3NaNO 3
Fe (OH) 3 - amphoteric hydroxide, insoluble in water, decomposes on heating into iron (III) oxide and water:
2Fe (OH) 3 → Fe 2 O 3 + 3H 2 O
When iron (III) oxide is fused with iron, iron (II) oxide is formed:
Fe 2 O 3 + Fe → 3FeO
Task number 3
The sodium was burned in air. The resulting substance was treated with hydrogen chloride on heating. The resulting simple yellow-green substance, when heated, reacted with chromium (III) oxide in the presence of potassium hydroxide. When a solution of one of the formed salts was treated with barium chloride, a yellow precipitate formed. Write the equations for the four reactions described.
1) When sodium is burned in air, sodium peroxide is formed:
2Na + O 2 → Na 2 O 2
2) When sodium peroxide interacts with hydrogen chloride, Cl 2 gas is released when heated:
Na 2 O 2 + 4HCl → 2NaCl + Cl 2 + 2H 2 O
3) In an alkaline environment, chlorine reacts when heated with amphoteric chromium oxide to form chromate and potassium chloride:
Cr 2 O 3 + 3Cl 2 + 10KOH → 2K 2 CrO 4 + 6KCl + 5H 2 O
2Cr +3 -6e → 2Cr +6 | ... 3 - oxidation
Cl 2 + 2e → 2Cl - | ... 1 - recovery
4) A yellow precipitate (BaCrO 4) is formed by the interaction of potassium chromate and barium chloride:
K 2 CrO 4 + BaCl 2 → BaCrO 4 ↓ + 2KCl
Task number 4
Zinc was completely dissolved in concentrated potassium hydroxide solution. The resulting clear solution was evaporated and then calcined. The solid residue was dissolved in the required amount of hydrochloric acid. Ammonium sulfide was added to the resulting clear solution and a white precipitate was observed. Write the equations for the four reactions described.
1) Zinc reacts with potassium hydroxide to form potassium tetrahydroxozincate (Al and Be behave similarly):
2) Potassium tetrahydroxozincate after calcination loses water and turns into potassium zincate:
3) Potassium zincate, when interacting with hydrochloric acid, forms zinc chloride, potassium chloride and water:
4) Zinc chloride, as a result of interaction with ammonium sulfide, turns into insoluble zinc sulfide - a white precipitate:
Task number 5
Hydroiodic acid was neutralized with potassium bicarbonate. The resulting salt was reacted with a solution containing potassium dichromate and sulfuric acid. When the formed simple substance interacted with aluminum, a salt was obtained. This salt was dissolved in water and mixed with potassium sulfide solution, resulting in a precipitate and gas evolution. Write the equations for the four reactions described.
1) Hydroiodic acid is neutralized by the acidic salt of weak carbonic acid, as a result of which carbon dioxide is released and NaCl is formed:
HI + KHCO 3 → KI + CO 2 + H 2 O
2) Potassium iodide enters into a redox reaction with potassium dichromate in an acidic medium, while Cr +6 is reduced to Cr +3, I is oxidized to molecular I 2, which precipitates:
6KI + K 2 Cr 2 O 7 + 7H 2 SO 4 → Cr 2 (SO 4) 3 + 4K 2 SO 4 + 3I 2 ↓ + 7H 2 O
2Cr +6 + 6e → 2Cr +3 │ 1
2I - -2e → I 2 │ 3
3) When molecular iodine interacts with aluminum, aluminum iodide is formed:
2Al + 3I 2 → 2AlI 3
4) When aluminum iodide interacts with a solution of potassium sulfide, Al (OH) 3 precipitates and H 2 S is released. The formation of Al 2 S 3 does not occur due to the complete hydrolysis of the salt in an aqueous solution:
2AlI 3 + 3K 2 S + 6H 2 O → 2Al (OH) 3 ↓ + 6KI + 3H 2 S
Task number 6
Aluminum carbide was completely dissolved in hydrobromic acid. To the resulting solution was added a solution of potassium sulfite, while the formation of a white precipitate and the evolution of a colorless gas were observed. The gas was absorbed with a solution of potassium dichromate in the presence of sulfuric acid. The formed chromium salt was isolated and added to the barium nitrate solution; precipitation was observed. Write the equations for the four reactions described.
1) When aluminum carbide is dissolved in hydrobromic acid, a salt is formed - aluminum bromide, and methane is released:
Al 4 C 3 + 12HBr → 4AlBr 3 + 3CH 4
2) When aluminum bromide interacts with a solution of potassium sulfite, Al (OH) 3 precipitates and sulfur dioxide - SO 2 is released:
2AlBr 3 + 3K 2 SO 3 + 3H 2 O → 2Al (OH) 3 ↓ + 6KBr + 3SO 2
3) Passing sulfur dioxide through an acidified solution of potassium dichromate, while Cr +6 is reduced to Cr +3, S +4 is oxidized to S +6:
3SO 2 + K 2 Cr 2 O 7 + H 2 SO 4 → Cr 2 (SO 4) 3 + K 2 SO 4 + H 2 O
2Cr +6 + 6e → 2Cr +3 │ 1
S +4 -2e → S +6 │ 3
4) When chromium (III) sulfate interacts with a solution of barium nitrate, chromium (III) nitrate is formed, and white barium sulfate precipitates:
Cr 2 (SO 4) 3 + 3Ba (NO 3) 2 → 3BaSO 4 ↓ + 2Cr (NO 3) 3
Task number 7
Aluminum powder was added to the sodium hydroxide solution. An excess of carbon dioxide was passed through the solution of the obtained substance. The formed precipitate was separated and calcined. The resulting product was fused with sodium carbonate. Write the equations for the four reactions described.
1) Aluminum, as well as beryllium and zinc, is capable of reacting both with aqueous solutions of alkalis and with anhydrous alkalis during fusion. When aluminum is treated with an aqueous solution of sodium hydroxide, sodium tetrahydroxoaluminate and hydrogen are formed:
2) When carbon dioxide is passed through an aqueous solution of sodium tetrahydroxoaluminate, crystalline aluminum hydroxide precipitates. Since, by condition, an excess of carbon dioxide is passed through the solution, not carbonate is formed, but sodium bicarbonate:
Na + CO 2 → Al (OH) 3 ↓ + NaHCO 3
3) Aluminum hydroxide is an insoluble metal hydroxide, therefore, when heated, it decomposes into the corresponding metal oxide and water:
4) Aluminum oxide, which is an amphoteric oxide, when fusion with carbonates displaces carbon dioxide from them with the formation of aluminates (not to be confused with tetrahydroxoaluminates!):
Task number 8
Aluminum reacted with sodium hydroxide solution. The evolved gas was passed over a heated copper (II) oxide powder. The resulting simple substance was dissolved by heating in concentrated sulfuric acid. The resulting salt was isolated and added to the potassium iodide solution. Write the equations for the four reactions described.
1) Aluminum (also beryllium and zinc) reacts both with aqueous solutions of alkalis and with anhydrous alkalis during fusion. When aluminum is treated with an aqueous solution of sodium hydroxide, sodium tetrahydroxoaluminate and hydrogen are formed:
2NaOH + 2Al + 6H 2 O → 2Na + 3H 2
2) When hydrogen is passed over a heated copper (II) oxide powder, Cu +2 is reduced to Cu 0: the color of the powder changes from black (CuO) to red (Cu):
3) Copper dissolves in concentrated sulfuric acid to form copper (II) sulfate. In addition, this produces sulfur dioxide:
4) When copper sulfate is added to a solution of potassium iodide, a redox reaction occurs: Cu +2 is reduced to Cu +1, I is oxidized to I 2 (molecular iodine precipitates):
CuSO 4 + 4KI → 2CuI + 2K 2 SO 4 + I 2 ↓
Task number 9
Conducted electrolysis of sodium chloride solution. Iron (III) chloride was added to the resulting solution. The formed precipitate was filtered off and calcined. The solid residue was dissolved in hydroiodic acid. Write the equations for the four reactions described.
1) Electrolysis of sodium chloride solution:
Cathode: 2H 2 O + 2e → H 2 + 2OH -
Anode: 2Cl - - 2e → Cl 2
Thus, as a result of its electrolysis, gaseous H 2 and Cl 2 are released from the sodium chloride solution, while Na + and OH - ions remain in the solution. In general terms, the equation is written as follows:
2H 2 O + 2NaCl → H 2 + 2NaOH + Cl 2
2) When iron (III) chloride is added to the alkali solution, an exchange reaction occurs, as a result of which Fe (OH) 3 precipitates:
3NaOH + FeCl 3 → Fe (OH) 3 ↓ + 3NaCl
3) When iron (III) hydroxide is calcined, iron (III) oxide and water are formed:
4) When iron (III) oxide is dissolved in hydroiodic acid, FeI 2 is formed, while I 2 precipitates:
Fe 2 O 3 + 6HI → 2FeI 2 + I 2 ↓ + 3H 2 O
2Fe +3 + 2e → 2Fe +2 │1
2I - - 2e → I 2 │1
Task number 10
Potassium chlorate was heated in the presence of a catalyst, while a colorless gas was evolved. By burning iron in an atmosphere of this gas, iron scale was obtained. It was dissolved in an excess of hydrochloric acid. To the resulting solution was added a solution containing sodium dichromate and hydrochloric acid.
1) When potassium chlorate is heated in the presence of a catalyst (MnO 2, Fe 2 O 3, CuO, etc.), potassium chloride is formed and oxygen is released:
2) When iron is burned in an oxygen atmosphere, iron scale is formed, the formula of which is Fe 3 O 4 (iron scale is a mixed oxide of Fe 2 O 3 and FeO):
3) When iron scale is dissolved in an excess of hydrochloric acid, a mixture of iron (II) and (III) chlorides is formed:
4) In the presence of a strong oxidizing agent - sodium dichromate, Fe +2 is oxidized to Fe +3:
6FeCl 2 + Na 2 Cr 2 O 7 + 14HCl → 6FeCl 3 + 2CrCl 3 + 2NaCl + 7H 2 O
Fe +2 - 1e → Fe +3 │6
2Cr +6 + 6e → 2Cr +3 │1
Task number 11
Ammonia was passed through hydrobromic acid. Silver nitrate solution was added to the resulting solution. The precipitate that formed was separated and heated with zinc powder. The metal formed during the reaction was acted upon with a concentrated solution of sulfuric acid, and gas with a pungent odor was released. Write the equations for the four reactions described.
1) When ammonia is passed through hydrobromic acid, ammonium bromide is formed (neutralization reaction):
NH 3 + HBr → NH 4 Br
2) When the solutions of ammonium bromide and silver nitrate are merged, an exchange reaction occurs between the two salts, as a result of which a light yellow precipitate - silver bromide:
NH 4 Br + AgNO 3 → AgBr ↓ + NH 4 NO 3
3) When silver bromide is heated with zinc powder, a substitution reaction occurs - silver is released:
2AgBr + Zn → 2Ag + ZnBr 2
4) When concentrated sulfuric acid acts on the metal, silver sulfate is formed and a gas with an unpleasant odor is released - sulfur dioxide:
2Ag + 2H 2 SO 4 (conc.) → Ag 2 SO 4 + SO 2 + 2H 2 O
2Ag 0 - 2e → 2Ag + │1
S +6 + 2e → S +4 │1
Task number 12
9S278S
Chromium (VI) oxide reacted with potassium hydroxide. The resulting substance was treated with sulfuric acid, and the orange salt was isolated from the resulting solution. This salt was treated with hydrobromic acid. The resulting simple substance reacted with hydrogen sulfide. Write the equations for the four reactions described.
1) Chromium (VI) oxide CrO 3 is an acidic oxide, therefore, it interacts with alkali to form a salt - potassium chromate:
CrO 3 + 2KOH → K 2 CrO 4 + H 2 O
2) Potassium chromate in an acidic medium is converted without changing the oxidation state of chromium into dichromate K 2 Cr 2 O 7 - an orange salt:
2K 2 CrO 4 + H 2 SO 4 → K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O
3) When processing potassium dichromate with hydrobromic acid, Cr +6 is reduced to Cr +3, while molecular bromine is released:
K 2 Cr 2 O 7 + 14HBr → 2CrBr 3 + 2KBr + 3Br 2 + 7H 2 O
2Cr +6 + 6e → 2Cr +3 │1
2Br - - 2e → Br 2 │3
4) Bromine, as a stronger oxidant, displaces sulfur from its hydrogen compound:
Br 2 + H 2 S → 2HBr + S ↓
Task number 13
Magnesium powder was heated under nitrogen atmosphere. When the resulting substance interacted with water, gas was released. The gas was passed through an aqueous solution of chromium (III) sulfate, resulting in the formation of a gray precipitate. The precipitate was separated and treated under heating with a solution containing hydrogen peroxide and potassium hydroxide. Write the equations for the four reactions described.
1) When magnesium powder is heated in a nitrogen atmosphere, magnesium nitride is formed:
2) Magnesium nitride is completely hydrolyzed to form magnesium hydroxide and ammonia:
Mg 3 N 2 + 6H 2 O → 3Mg (OH) 2 ↓ + 2NH 3
3) Ammonia has basic properties due to the presence of a lone electron pair at the nitrogen atom and, as a base, enters into an exchange reaction with chromium (III) sulfate, which results in a gray precipitate - Cr (OH) 3:
6NH 3. H 2 O + Cr 2 (SO 4) 3 → 2Cr (OH) 3 ↓ + 3 (NH 4) 2 SO 4
4) Hydrogen peroxide in an alkaline medium oxidizes Cr +3 to Cr +6, resulting in the formation of potassium chromate:
2Cr (OH) 3 + 3H 2 O 2 + 4KOH → 2K 2 CrO 4 + 8H 2 O
Cr +3 -3e → Cr +6 │2
2O - + 2e → 2O -2 │3
Task number 14
The interaction of aluminum oxide with nitric acid formed a salt. The salt was dried and calcined. The solid residue formed during calcination was subjected to electrolysis in molten cryolite. The metal obtained by electrolysis was heated with a concentrated solution containing potassium nitrate and potassium hydroxide, while a gas with a pungent odor was released. Write the equations for the four reactions described.
1) When amphoteric Al 2 O 3 interacts with nitric acid, a salt is formed - aluminum nitrate (exchange reaction):
Al 2 O 3 + 6HNO 3 → 2Al (NO 3) 3 + 3H 2 O
2) When aluminum nitrate is calcined, aluminum oxide is formed, and nitrogen dioxide and oxygen are released (aluminum belongs to the group of metals (in the range of activity from alkaline earth to Cu, inclusive), the nitrates of which decompose to metal oxides, NO 2 and O 2):
3) Metallic aluminum is formed during the electrolysis of Al 2 O 3 in molten cryolite Na 2 AlF 6 at 960-970 o C.
Al 2 O 3 electrolysis scheme:
Dissociation of aluminum oxide occurs in the melt:
Al 2 O 3 → Al 3+ + AlO 3 3-
K (-): Al 3+ + 3e → Al 0
A (+): 4AlO 3 3- - 12e → 2Al 2 O 3 + 3O 2
The overall equation of the process:
Liquid aluminum collects at the bottom of the cell.
4) When processing aluminum with a concentrated alkaline solution containing potassium nitrate, ammonia is released, and potassium tetrahydroxoaluminate is also formed (alkaline medium):
8Al + 5KOH + 3KNO 3 + 18H 2 O → 3NH 3 + 8K
Al 0 - 3e → Al +3 │8
N +5 + 8e → N -3 │3
Task number 15
8AAA8C
Some of the iron (II) sulfide was divided into two parts. One of them was treated with hydrochloric acid, and the other was fired in air. The interaction of the evolved gases formed a simple yellow substance. The resulting substance was heated with concentrated nitric acid, while a brown gas was evolved. Write the equations for the four reactions described.
1) When treating iron (II) sulfide with hydrochloric acid, iron (II) chloride is formed and hydrogen sulfide is released (exchange reaction):
FeS + 2HCl → FeCl 2 + H 2 S
2) When roasting iron (II) sulfide, iron is oxidized to the oxidation state +3 (Fe 2 O 3 is formed) and sulfur dioxide is released:
3) When two sulfur-containing compounds SO 2 and H 2 S interact, a redox reaction (coproportionation) occurs, as a result of which sulfur is released:
2H 2 S + SO 2 → 3S ↓ + 2H 2 O
S -2 - 2e → S 0 │2
S +4 + 4e → S 0 │1
4) When sulfur is heated with concentrated nitric acid, sulfuric acid and nitrogen dioxide are formed (redox reaction):
S + 6HNO 3 (conc.) → H 2 SO 4 + 6NO 2 + 2H 2 O
S 0 - 6e → S +6 │1
N +5 + e → N +4 │6
Task number 16
The gas obtained by treating calcium nitride with water was passed over a red-hot powder of copper (II) oxide. The resulting solid was dissolved in concentrated nitric acid, the solution was evaporated, and the resulting solid was calcined. Write the equations for the four reactions described.
1) Calcium nitride reacts with water to form alkali and ammonia:
Ca 3 N 2 + 6H 2 O → 3Ca (OH) 2 + 2NH 3
2) Passing ammonia over a red-hot powder of copper (II) oxide, copper in the oxide is reduced to metallic, while nitrogen is released (hydrogen, coal, carbon monoxide, etc. are also used as reducing agents):
Cu +2 + 2e → Cu 0 │3
2N -3 - 6e → N 2 0 │1
3) Copper, located in the row of metal activities after hydrogen, reacts with concentrated nitric acid to form copper nitrate and nitrogen dioxide:
Cu + 4HNO 3 (conc.) → Cu (NO 3) 2 + 2NO 2 + 2H 2 O
Cu 0 - 2e → Cu +2 │1
N +5 + e → N +4 │2
4) When copper nitrate is calcined, copper oxide is formed, and nitrogen dioxide and oxygen are released (copper belongs to the group of metals (in the range of activity from alkaline earth to Cu, inclusive), the nitrates of which decompose to metal oxides, NO 2 and O 2):
Task number 17
Silicon was burned in a chlorine atmosphere. The resulting chloride was treated with water. The precipitate that formed was calcined. Then fused with calcium phosphate and coal. Write the equations for the four reactions described.
1) Silicon react with chlorine at a temperature of 340-420 o C in a stream of argon to form silicon (IV) chloride:
2) Silicon (IV) chloride is completely hydrolyzed, while hydrochloric acid is formed, and silicic acid precipitates:
SiCl 4 + 3H 2 O → H 2 SiO 3 ↓ + 4HCl
3) When calcined, silicic acid decomposes to silicon oxide (IV) and water:
4) When silicon dioxide is fused with coal and calcium phosphate, a redox reaction occurs, as a result of which calcium silicate, phosphorus are formed, and carbon monoxide is also released:
C 0 - 2e → C +2 │10
4P +5 + 20e → P 4 0 │1
Task number 18
Note! This format of tasks is outdated, but nevertheless tasks of this type deserve attention, since in fact they require writing the same equations that are found in the CMMs of the USE of the new format.
Substances are given: iron, iron scale, dilute hydrochloric and concentrated nitric acids. Write the equations of four possible reactions between all the proposed substances, without repeating pairs of reagents.
1) Hydrochloric acid reacts with iron, oxidizing it to the oxidation state +2, while hydrogen is released (substitution reaction):
Fe + 2HCl → FeCl 2 + H 2
2) Concentrated nitric acid passivates iron (i.e., a strong protective oxide film forms on its surface), however, under the influence of high temperature, iron is oxidized with concentrated nitric acid to an oxidation state of +3:
3) Formula of iron scale - Fe 3 O 4 (a mixture of iron oxides FeO and Fe 2 O 3). Fe 3 O 4 enters into an exchange reaction with hydrochloric acid, and a mixture of two chlorides of iron (II) and (III) is formed:
Fe 3 O 4 + 8HCl → 2FeCl 3 + FeCl 2 + 4H 2 O
4) In addition, iron scale enters into a redox reaction with concentrated nitric acid, while the Fe +2 contained in it is oxidized to Fe +3:
Fe 3 O 4 + 10HNO 3 (conc.) → 3Fe (NO 3) 3 + NO 2 + 5H 2 O
5) Iron scale and iron, when sintered, enter into a proportional reaction (the same chemical element acts as an oxidizing agent and a reducing agent):
Task number 19
Substances are given: phosphorus, chlorine, aqueous solutions of sulfuric acid and potassium hydroxide. Write the equations of four possible reactions between all suggested substances without repeating pairs of reagents.
1) Chlorine is a poisonous gas with high chemical activity, it reacts especially vigorously with red phosphorus. In an atmosphere of chlorine, phosphorus ignites spontaneously and burns with a weak greenish flame. Depending on the ratio of the reactants, phosphorus (III) chloride or phosphorus (V) chloride can be obtained:
2P (red) + 3Cl 2 → 2PCl 3
2P (red) + 5Cl 2 → 2PCl 5
Cl 2 + 2KOH → KCl + KClO + H 2 O
If chlorine is passed through a hot concentrated alkali solution, molecular chlorine disproportionates into Cl +5 and Cl -1, resulting in the formation of chlorate and chloride, respectively:
3) As a result of the interaction of aqueous solutions of alkali and sulfuric acid, an acidic or medium salt of sulfuric acid is formed (depending on the concentration of reagents):
KOH + H 2 SO 4 → KHSO 4 + H 2 O
2KOH + H 2 SO 4 → K 2 SO 4 + 2H 2 O (neutralization reaction)
4) Strong oxidants such as sulfuric acid convert phosphorus to phosphoric acid:
2P + 5H 2 SO 4 → 2H 3 PO 4 + 5SO 2 + 2H 2 O
Task number 20
Substances are given: nitric oxide (IV), copper, potassium hydroxide solution and concentrated sulfuric acid. Write the equations of four possible reactions between all the proposed substances, without repeating pairs of reagents.
1) Copper, located in the row of metal activities to the right of hydrogen, is capable of being oxidized by strong oxidizing acids (H 2 SO 4 (conc.), HNO 3, etc.):
Cu + 2H 2 SO 4 (conc.) → CuSO 4 + SO 2 + 2H 2 O
2) As a result of the interaction of the KOH solution with concentrated sulfuric acid, an acidic salt is formed - potassium hydrogen sulfate:
KOH + H 2 SO 4 (conc.) → KHSO 4 + H 2 O
3) When passing brown gas, NO 2 N +4 disproportionates to N +5 and N +3, resulting in the formation of potassium nitrate and nitrite, respectively:
2NO 2 + 2KOH → KNO 3 + KNO 2 + H 2 O
4) When brown gas is passed through a concentrated solution of sulfuric acid, N +4 is oxidized to N +5 and sulfur dioxide is released:
2NO 2 + H 2 SO 4 (conc.) → 2HNO 3 + SO 2
Task number 21
Substances are given: chlorine, sodium hydrosulfide, potassium hydroxide (solution), iron. Write the equations of four possible reactions between all suggested substances without repeating pairs of reagents.
1) Chlorine, being a strong oxidizing agent, reacts with iron, oxidizing it to Fe +3:
2Fe + 3Cl 2 → 2FeCl 3
2) When chlorine is passed through a cold concentrated alkali solution, chloride and hypochlorite are formed (molecular chlorine disproportionates to Cl +1 and Cl -1):
2KOH + Cl 2 → KCl + KClO + H 2 O
If chlorine is passed through a hot concentrated alkali solution, molecular chlorine disproportionates to Cl +5 and Cl -1, resulting in the formation of chlorate and chloride, respectively:
3Cl 2 + 6KOH → 5KCl + KClO 3 + 3H 2 O
3) Chlorine, which has stronger oxidizing properties, is able to oxidize the sulfur included in the acid salt:
Cl 2 + NaHS → NaCl + HCl + S ↓
4) Acid salt - sodium hydrosulfide in an alkaline medium turns into sulfide:
2NaHS + 2KOH → K 2 S + Na 2 S + 2H 2 O
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