Qualitative Analysis

1. A solid X has the following properties. (i) It is insoluble in water (ii) It gives off a gas when heated. (iii) It gives a gas when added to dilute sulfuric acid. Which one of the following could X be?

Calcium hydroxide

Copper (II) carbonate

Sodium carbonate

Zinc oxide

Copper (II) carbonate is the correct answer because it fits all the given properties. It is insoluble in water, as indicated by property (i). When heated, it decomposes and gives off carbon dioxide gas, satisfying property (ii). Additionally, when added to dilute sulfuric acid, it also produces carbon dioxide gas, fulfilling property (iii). Calcium hydroxide, sodium carbonate, and zinc oxide do not exhibit all of these properties, making copper (II) carbonate the most suitable option.

Explanation

Copper (II) carbonate is the correct answer because it fits all the given properties. It is insoluble in water, as indicated by property (i). When heated, it decomposes and gives off carbon dioxide gas, satisfying property (ii). Additionally, when added to dilute sulfuric acid, it also produces carbon dioxide gas, fulfilling property (iii). Calcium hydroxide, sodium carbonate, and zinc oxide do not exhibit all of these properties, making copper (II) carbonate the most suitable option.

2. A pale green solution X gives a green precipitate with excess aqueous sodium hydroxide. An alkaline gas is only given off when the mixture is warmed with powdered aluminum. Which ion does X contain?

Ammonium and copper(II)

Ammonium and iron (III)

Copper (II) and nitrate

Iron (II) and nitrate

Pale green solution: Iron(II) ions (Fe²⁺) in solution often appear pale green.

Green precipitate with excess aqueous sodium hydroxide: Iron(II) hydroxide, Fe(OH)₂, forms a green precipitate when iron(II) ions react with sodium hydroxide.

Alkaline gas given off when warmed with powdered aluminum: This indicates the presence of nitrate ions (NO₃⁻). When nitrates are warmed with powdered aluminum in an alkaline solution, ammonia gas (NH₃) is released.

Explanation

Pale green solution: Iron(II) ions (Fe²⁺) in solution often appear pale green.

Green precipitate with excess aqueous sodium hydroxide: Iron(II) hydroxide, Fe(OH)₂, forms a green precipitate when iron(II) ions react with sodium hydroxide.

Alkaline gas given off when warmed with powdered aluminum: This indicates the presence of nitrate ions (NO₃⁻). When nitrates are warmed with powdered aluminum in an alkaline solution, ammonia gas (NH₃) is released.

3. What reaction occurs when aqueous copper (II) sulfate is added to aqueous sodium hydroxide?

Displacement

Redox

Precipitation

Neutralisation

When aqueous copper (II) sulfate is added to aqueous sodium hydroxide, a precipitation reaction occurs. This means that a solid substance, called a precipitate, is formed. In this case, the precipitate formed is copper (II) hydroxide, which is insoluble in water. The reaction can be represented by the following equation: CuSO4 (aq) + 2NaOH (aq) → Cu(OH)2 (s) + Na2SO4 (aq).

Explanation

When aqueous copper (II) sulfate is added to aqueous sodium hydroxide, a precipitation reaction occurs. This means that a solid substance, called a precipitate, is formed. In this case, the precipitate formed is copper (II) hydroxide, which is insoluble in water. The reaction can be represented by the following equation: CuSO4 (aq) + 2NaOH (aq) → Cu(OH)2 (s) + Na2SO4 (aq).

4. Two bottles in a laboratory are unlabelled. One bottle is known to contain aqueous sodium iodide and the other aqueous sodium chloride. What test would identify the solutions?

Adition of aqueous lead (II) nitrate

Addition of dilute sulfuric acid

Addition of blue litmus paper.

Addition of sodium hydroxide

Adding aqueous lead (II) nitrate to the solutions would identify the solutions. This is because when lead (II) nitrate is added to a solution containing iodide ions (such as the one with aqueous sodium iodide), a yellow precipitate of lead (II) iodide is formed. On the other hand, if lead (II) nitrate is added to a solution containing chloride ions (such as the one with aqueous sodium chloride), a white precipitate of lead (II) chloride is formed. Therefore, by observing the color of the precipitate formed, we can identify which solution contains sodium iodide and which contains sodium chloride.

Explanation

Adding aqueous lead (II) nitrate to the solutions would identify the solutions. This is because when lead (II) nitrate is added to a solution containing iodide ions (such as the one with aqueous sodium iodide), a yellow precipitate of lead (II) iodide is formed. On the other hand, if lead (II) nitrate is added to a solution containing chloride ions (such as the one with aqueous sodium chloride), a white precipitate of lead (II) chloride is formed. Therefore, by observing the color of the precipitate formed, we can identify which solution contains sodium iodide and which contains sodium chloride.

5. Which of the following CANNOT be used to distinguish between aqueous lead (II) nitrate and aqueous aluminium nitrate?

Dilute hydrochloric acid

Dilute sulfuric acid

Aqueous potassium iodide

Aqueous sodium hydroxide

Aqueous sodium hydroxide cannot be used to distinguish between aqueous lead (II) nitrate and aqueous aluminium nitrate because both lead (II) nitrate and aluminium nitrate will form white precipitates when reacted with aqueous sodium hydroxide. Therefore, this test will not provide a reliable distinction between the two compounds.

Explanation

Aqueous sodium hydroxide cannot be used to distinguish between aqueous lead (II) nitrate and aqueous aluminium nitrate because both lead (II) nitrate and aluminium nitrate will form white precipitates when reacted with aqueous sodium hydroxide. Therefore, this test will not provide a reliable distinction between the two compounds.

6. Which two gases each change the colour of damp blue litmus paper?

Ammonia and chlorine

Oxygen and hydrogen chloride

Carbon dioxide and hydrogen

Carbon dioxide and chlorine

Carbon dioxide and chlorine are the two gases that change the color of damp blue litmus paper. Carbon dioxide turns the litmus paper pink, indicating acidity, while chlorine turns it white, indicating the presence of a strong oxidizing agent.

Explanation

Carbon dioxide and chlorine are the two gases that change the color of damp blue litmus paper. Carbon dioxide turns the litmus paper pink, indicating acidity, while chlorine turns it white, indicating the presence of a strong oxidizing agent.

7. Which of the following pairs of solutions give a white precipitate when mixed?

Sodium chloride and lead (II) nitrate

Barium nitrate and calcium chloride

Iron (II) chloride and sodium hydroxide

Sodium sulfate and aluminium chloride

When sodium chloride and lead (II) nitrate are mixed, a white precipitate of lead chloride is formed. This is because lead chloride is insoluble in water and therefore forms a solid precipitate.

Explanation

When sodium chloride and lead (II) nitrate are mixed, a white precipitate of lead chloride is formed. This is because lead chloride is insoluble in water and therefore forms a solid precipitate.

8. Dilute HCl was added to a tube containing an unknown powder. The powder dissolved with no effervescence observed. After the reaction stopped, excess aqueous sodium hydroxide was added to the tube and a white precipitate formed. What was the unknown powder?

Zinc oxide

Lead (II) oxide

Calcium oxide

Calcium carbonate

The correct answer is calcium oxide. When dilute HCl is added to calcium oxide, it reacts to form calcium chloride and water. This reaction does not produce any gas, so no effervescence is observed. When excess aqueous sodium hydroxide is added to the tube, it reacts with the remaining calcium chloride to form calcium hydroxide, which is insoluble in water and appears as a white precipitate. This confirms that the unknown powder was calcium oxide.

Explanation

The correct answer is calcium oxide. When dilute HCl is added to calcium oxide, it reacts to form calcium chloride and water. This reaction does not produce any gas, so no effervescence is observed. When excess aqueous sodium hydroxide is added to the tube, it reacts with the remaining calcium chloride to form calcium hydroxide, which is insoluble in water and appears as a white precipitate. This confirms that the unknown powder was calcium oxide.

9. Under suitable conditions, dilute HCl reacts with each of the following substances. Which reaction gives a colourless solution only?

Aqueous silver nitrate

Calcium carbonate

Copper (II) oxide

Limewater

Limewater is the only substance among the options that gives a colorless solution when reacted with dilute HCl. Aqueous silver nitrate produces a white precipitate of silver chloride, calcium carbonate reacts to form a white precipitate of calcium chloride, copper (II) oxide forms a blue solution due to the formation of copper chloride, while limewater reacts with HCl to form calcium chloride, which remains in solution and does not produce any visible color change.

Explanation

Limewater is the only substance among the options that gives a colorless solution when reacted with dilute HCl. Aqueous silver nitrate produces a white precipitate of silver chloride, calcium carbonate reacts to form a white precipitate of calcium chloride, copper (II) oxide forms a blue solution due to the formation of copper chloride, while limewater reacts with HCl to form calcium chloride, which remains in solution and does not produce any visible color change.

10. Excess barium nitrate is added to dilute sulfuric acid. The precipitate formed is removed by filtration. What ions are present in the filtrate?

Ba2+ and NO3-

Ba2+, H+ and NO3-

H+ and NO3-

H+, NO3- and SO42-

When excess barium nitrate is added to dilute sulfuric acid, a reaction occurs between the barium nitrate and sulfuric acid, resulting in the formation of a precipitate. The precipitate is then removed by filtration, leaving behind the ions that were present in the filtrate. Since barium nitrate is a salt composed of Ba2+ and NO3- ions, and sulfuric acid is an acid composed of H+ and SO42- ions, the ions present in the filtrate would be Ba2+, H+, and NO3-.

Explanation

When excess barium nitrate is added to dilute sulfuric acid, a reaction occurs between the barium nitrate and sulfuric acid, resulting in the formation of a precipitate. The precipitate is then removed by filtration, leaving behind the ions that were present in the filtrate. Since barium nitrate is a salt composed of Ba2+ and NO3- ions, and sulfuric acid is an acid composed of H+ and SO42- ions, the ions present in the filtrate would be Ba2+, H+, and NO3-.