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Quiz Chapter 6: Acid, Base and Salt

10 questions ยท Form 4 Chemistry Bab 4: Acid, Base and Salt

Question 1 of 10Score: 0

A solid salt X is heated strongly. It yields a brown gas that turns moist blue litmus paper red, and leaves a residue that is YELLOW when hot and WHITE when cold. What is salt X?

Full Question List & Answer Key

Prefer reading to quizzing? All 10 questions are listed below with the answer and explanation under each one.

1. A solid salt X is heated strongly. It yields a brown gas that turns moist blue litmus paper red, and leaves a residue that is YELLOW when hot and WHITE when cold. What is salt X?

  1. Copper(II) nitrate
  2. Lead(II) nitrate
  3. Zinc nitrate
  4. Zinc carbonate
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Answer: C

Brown gas is NO2 (from nitrate). Oxide residue that is yellow when hot and white when cold is Zinc oxide (ZnO). Thus, salt X is Zinc nitrate.

2. Which reagent is used to confirm the presence of chloride ions (Cl-) in an aqueous solution?

  1. Barium chloride solution acidified with hydrochloric acid
  2. Silver nitrate solution acidified with dilute nitric acid
  3. Iron(II) sulfate solution and concentrated sulfuric acid
  4. Potassium iodide solution
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Answer: B

Acidifying with dilute HNO3 and adding AgNO3 yields a white precipitate of AgCl if Cl- ions are present.

3. Which reagent can be used to distinguish between Aluminium ion (Al3+) and Lead(II) ion (Pb2+) solutions?

  1. Sodium hydroxide solution
  2. Potassium iodide solution
  3. Dilute nitric acid
  4. Ammonia solution
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Answer: B

Potassium iodide (KI) reacts with Pb2+ to form a bright yellow precipitate (PbI2), whereas no precipitate forms with Al3+.

4. Which salt can be prepared using the acid + alkali titration method?

  1. Copper(II) sulfate
  2. Potassium nitrate
  3. Lead(II) chloride
  4. Zinc carbonate
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Answer: B

Potassium nitrate (KNO3) is a soluble SPAN salt (Potassium), so it must be prepared via titration.

5. Why does glacial ethanoic acid dissolved in dry propanone fail to turn dry blue litmus paper red?

  1. Ethanoic acid is too concentrated to react
  2. Absence of water prevents the acid from ionising to release free-moving hydrogen ions (H+)
  3. Propanone neutralises the ethanoic acid molecules
  4. Glacial ethanoic acid is a strong alkali when dissolved in organic solvents
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Answer: B

Acids require water to ionise and produce hydrogen ions (H+), which are responsible for displaying acidic properties.

6. Which salt is INSOLUBLE in water at room temperature?

  1. Barium chloride (BaCl2)
  2. Lead(II) sulfate (PbSO4)
  3. Potassium nitrate (KNO3)
  4. Sodium carbonate (Na2CO3)
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Answer: B

Lead(II) sulfate (PbSO4) is one of the insoluble sulfates (PBC: PbSO4, BaSO4, CaSO4).

7. What volume of water must be added to 50 cm3 of 2.0 mol dm-3 NaOH solution to dilute it to 0.5 mol dm-3?

  1. 150 cm3
  2. 200 cm3
  3. 100 cm3
  4. 250 cm3
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Answer: A

Using M1V1 = M2V2: (2.0)(50) = (0.5)(V2) => V2 = 200 cm3 total volume. Volume of water to add = 200 - 50 = 150 cm3.

8. What observation confirms the formation of a brown ring in the confirmatory test for nitrate ions (NO3-)?

  1. A brown precipitate settling at the bottom of the test tube
  2. A brown gas escaping from the mouth of the test tube
  3. A brown ring forming at the boundary between two liquid layers
  4. The entire solution turning dark brown immediately
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Answer: C

The nitrate brown ring test forms a distinct brown ring of [Fe(H2O)5(NO)]2+ at the junction of the concentrated sulfuric acid and aqueous layer.

9. What is the pH value of a 0.01 mol dm-3 hydrochloric acid (HCl) solution?

  1. 1.0
  2. 2.0
  3. 12.0
  4. 13.0
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Answer: B

pH = -log[H+]. For 0.01 mol dm-3 HCl (10-2 mol dm-3), pH = -log(0.01) = 2.0.

10. When sodium hydroxide (NaOH) solution is added until excess to an unknown cation solution, a white precipitate forms which DISSOLVES in excess NaOH. Adding aqueous ammonia (NH3) until excess also produces a white precipitate which DISSOLVES in excess NH3. Which cation is present?

  1. Al3+
  2. Pb2+
  3. Zn2+
  4. Mg2+
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Answer: C

Zinc ion (Zn2+) is the only cation whose white hydroxide precipitate dissolves in EXCESS of both NaOH and NH3 solutions.

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