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Chemistry · Practice book · Senior 2 · Unit 9 of 9

Chemical properties of acids and bases

Senior 2 Chemistry · 14 questions with answers. Try each question on paper, then tap it to see the answer.

Unit 9 Chemical properties of acids and bases

Key unit competence: Apply knowledge of the preparation and properties of acids and bases to explain their reactions and uses in daily life.

Key ideas

  • Acids can be prepared by dissolving acidic oxides in water (SO3 + H2O → H2SO4, CO2 + H2O → H2CO3), by direct combination (H2 + Cl2 → 2HCl, then dissolving) or by displacement with a less volatile acid. Bases are prepared by burning metals in oxygen, reacting metals with water (2Na + 2H2O → 2NaOH + H2) or dissolving basic oxides in water.
  • Acid + metal (above hydrogen) → salt + hydrogen: Mg + 2HCl → MgCl2 + H2.
  • Acid + metal oxide or hydroxide (base) → salt + water: CuO + H2SO4 → CuSO4 + H2O.
  • Acid + carbonate or hydrogencarbonate → salt + water + carbon dioxide: CaCO3 + 2HCl → CaCl2 + H2O + CO2; NaHCO3 + HCl → NaCl + H2O + CO2.
  • Alkalis react with acids (neutralisation), with ammonium salts on warming to give ammonia (NH4Cl + NaOH → NaCl + H2O + NH3) and with solutions of many metal ions to give hydroxide precipitates.
  • Uses: sulfuric acid in car batteries and fertilisers, hydrochloric acid in cleaning metals, citric and ethanoic acids in food, sodium hydroxide in soap making, calcium hydroxide in agriculture and building, ammonia in fertilisers and cleaners, magnesium hydroxide in antacids. Dangers: corrosive burns, eye damage, toxic fumes; store and label safely.

Common misconceptions

  • "All metals react with acids to give hydrogen." No: Metals below hydrogen (Cu, Ag, Au) do not displace hydrogen from dilute acids.
  • "Acids react with carbonates to give hydrogen." No: Carbonates give carbon dioxide, water and a salt.
  • "Neutralisation always gives a solution with pH exactly 7." No: Only if the exact amounts are used, and some salts give slightly acidic or alkaline solutions.

Worked examples

Example 1. Write balanced equations for the reaction of dilute hydrochloric acid with (a) zinc, (b) copper(II) oxide, (c) sodium carbonate.

Solution

(a) Zn + 2HCl → ZnCl2 + H2.

(b) CuO + 2HCl → CuCl2 + H2O.

(c) Na2CO3 + 2HCl → 2NaCl + H2O + CO2.

Example 2. Describe how you would show that a white powder is a carbonate.

Solution

Add dilute hydrochloric acid to the powder: it fizzes.

Pass the gas produced into limewater.

The limewater turns milky: the gas is carbon dioxide, so the powder is a carbonate.

Practice questions

  1. Write the word equation for the reaction between iron and dilute sulfuric acid.

    Show answer

    Iron + sulfuric acid → iron(II) sulfate + hydrogen.

    Common mistake: Writing iron(III) sulfate.

  2. Name the gas produced when an acid reacts with a hydrogencarbonate.

    Show answer

    Carbon dioxide.

    Common mistake: Writing hydrogen.

  3. Give one method of preparing an alkali.

    Show answer

    Dissolve a soluble basic oxide in water, e.g. Na2O + H2O → 2NaOH, or react a reactive metal with water.

    Common mistake: Adding a metal to an acid.

  4. State two uses of sulfuric acid.

    Show answer

    Car batteries, fertilisers, detergents, paints (any two).

    Common mistake: Saying it is used in cooking.

  5. Why do farmers not apply lime and ammonium fertiliser at the same time?

    Show answer

    Lime reacts with ammonium salts, releasing ammonia gas, so nitrogen is lost.

    Common mistake: Saying lime makes the fertiliser acidic.

  6. Write the balanced equation for Ca(OH)2 reacting with HCl.

    Show answer

    Ca(OH)2 + 2HCl → CaCl2 + 2H2O.

    Common mistake: Writing CaCl.

  7. Explain why stomach acid can be neutralised by milk of magnesia.

    Show answer

    Milk of magnesia is magnesium hydroxide, a base that neutralises HCl.

    Common mistake: Saying it is an acid.

  8. Write the equation for sodium hydrogencarbonate with HCl.

    Show answer

    NaHCO3 + HCl → NaCl + H2O + CO2.

    Common mistake: Writing Na2CO3 as the product.

  9. Give two safety precautions when using concentrated acids.

    Show answer

    Wear goggles and gloves; add acid to water; use a fume cupboard; store away from bases (any two).

    Common mistake: Saying 'taste to check'.

  10. What mass of zinc chloride (Mr 136) forms from 6.5 g of zinc (Ar 65)?

    Show answer

    0.1 mol × 136 = 13.6 g.

    Common mistake: Using Mr of zinc only.

Matching and drag-and-drop

  1. Matching

    Match each item in column A with the correct answer in column B. Write the letter next to each number.

    Column AColumn B
    1. Acid + carbonate → salt + water + ______a. SO3
    2. Which reaction produces a salt, water and carbon dioxide?b. carbon dioxide
    3. Sulfuric acid can be made by dissolving which oxide in water?c. reacts with metal oxides to form soluble salts
    4. Hydrochloric acid is used to clean rust from metals because it:d. Sodium hydrogencarbonate + ethanoic acid
    Show answer

    1 → b (carbon dioxide) · 2 → d (Sodium hydrogencarbonate + ethanoic acid) · 3 → a (SO3) · 4 → c (reacts with metal oxides to form soluble salts)

    • Carbonates release CO2.
    • Hydrogencarbonates give CO2.
    • SO3 + H2O → H2SO4.
    • Fe2O3 + 6HCl → 2FeCl3 + 3H2O.

  2. Drag and drop

    Choose the correct word or phrase from the box for each gap. One word in the box is not needed.

    calcium chloride  ·  calcium sulfate  ·  carbon dioxide gas is produced  ·  squeaky pop
    1. The gas produced when zinc reacts with HCl burns with a .
    2. The salt formed from calcium carbonate and hydrochloric acid is .
    3. Baking powder contains sodium hydrogencarbonate and a weak acid. When wet, it makes bread rise because .
    Show answer

    1: squeaky pop · 2: calcium chloride · 3: carbon dioxide gas is produced

    • Hydrogen burns with a pop.
    • CaCO3 + 2HCl → CaCl2 + H2O + CO2.
    • Acid + hydrogencarbonate → CO2.

  3. Matching

    Match each item in column A with the correct answer in column B. Write the letter next to each number.

    Column AColumn B
    1. What happens to the pH of an acid as an alkali is gradually added?a. Mg + H2SO4 → MgSO4 + H2
    2. Which is a danger of concentrated sodium hydroxide?b. It causes severe burns to skin and eyes
    3. Acid + base → salt + ______c. water
    4. Which balanced equation is correct?d. It rises
    Show answer

    1 → d (It rises) · 2 → b (It causes severe burns to skin and eyes) · 3 → c (water) · 4 → a (Mg + H2SO4 → MgSO4 + H2)

    • The H+ ions are neutralised.
    • It is strongly corrosive.
    • This is neutralisation.
    • One Mg and one H2SO4 give one MgSO4 and one H2.

  4. Drag and drop

    Choose the correct word or phrase from the box for each gap. One word in the box is not needed.

    Sulfuric acid  ·  water  ·  Ammonia  ·  chlorine
    1. Sodium hydroxide can be made by reacting sodium with .
    2. Which acid is found in car batteries? →
    3. Which gas is given off when ammonium chloride is warmed with sodium hydroxide? →
    Show answer

    1: water · 2: Sulfuric acid · 3: Ammonia

    • 2Na + 2H2O → 2NaOH + H2.
    • Lead–acid batteries use dilute sulfuric acid.
    • Alkalis release ammonia from ammonium salts.

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