Secondary 3 Chemistry Acids Bases Salts Quiz

Secondary 3 Chemistry Quiz - Acids Bases Salts

Name: _________________ Class: _________ Date: _________

Score: _____ / 25 marks Duration: 30 minutes

Instructions:

• Answer all questions in the spaces provided
• Show all working for calculations
• Use appropriate chemical formulae and equations where required

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Section A: Short Answer Questions [8 marks]

1. Which solid compound is added to soil to increase the pH? [1]

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2. What is meant by the term monatomic? [1]

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3. State the atom in CFCs that is responsible for ozone layer depletion. [1]

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4. Which two compounds can be reacted together to form an ammonium salt? [1]

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Section B: Structured Questions [12 marks]

5. A student performs a titration to find the concentration of hydrochloric acid. The results are shown below:

Trial	Volume of NaOH used (cm³)
Rough	24.8
1	24.2
2	24.1
3	24.3

(a) Based on the best titration results, calculate the average volume of NaOH required for complete neutralization. [1]

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(b) The concentration of NaOH used is 0.100 mol/dm³. Calculate the number of moles of NaOH in 25.0 cm³ of this solution. [1]

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(c) Using the balanced equation HCl + NaOH → NaCl + H₂O, calculate the number of moles of HCl that reacted. [1]

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6. Sodium bromide has a melting point of 747°C while tetrabromomethane has a melting point of 91°C.

Explain, in terms of structure and bonding, why sodium bromide has a much higher melting point than tetrabromomethane. [3]

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7. An unknown compound X shows amphoteric properties.

(a) State what is meant by amphoteric. [1]

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(b) Name a strong acid that compound X would react with. [1]

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(c) Name a strong alkali that compound X would react with. [1]

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Section C: Calculation and Analysis [5 marks]

8. A solution R contains 6.30 g/dm³ of a monoprotic organic acid. In a titration, 25.0 cm³ of R required 21.5 cm³ of 0.150 mol/dm³ sodium hydroxide for complete neutralization.

(a) Calculate the number of moles of NaOH used in the titration. [1]

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(b) Calculate the number of moles of the organic acid in 25.0 cm³ of R. [1]

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(c) Calculate the number of moles of the organic acid in 1.00 dm³ of R. [1]

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(d) Using your answer to (c) and the given concentration, calculate the relative molecular mass of the organic acid. [1]

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9. Draw the 'dot and cross' diagram to show the bonding in ammonia (NH₃). Show only the valence electrons. [1]

Secondary 3 Chemistry Quiz - Acids Bases Salts - ANSWERS

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Section A: Short Answer Questions [8 marks]

1. Which solid compound is added to soil to increase the pH? [1]

Answer: Calcium oxide / CaO OR Calcium hydroxide / Ca(OH)₂ OR Calcium carbonate / CaCO₃ Mark: Accept any of these compounds (1 mark)

2. What is meant by the term monatomic? [1]

Answer: Consisting of a single atom per particle/molecule Mark: Must mention "single atom" and "per particle" or equivalent (1 mark)

3. State the atom in CFCs that is responsible for ozone layer depletion. [1]

Answer: Chlorine / Cl Mark: Accept "chlorine" or "Cl" (1 mark)

4. Which two compounds can be reacted together to form an ammonium salt? [1]

Answer: Ammonia and an acid OR NH₃ and HCl (or any acid) Mark: Must name both reactants - ammonia/NH₃ + acid (1 mark)

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Section B: Structured Questions [12 marks]

5. Titration calculation

(a) Average volume calculation [1] Answer: (24.2 + 24.1 + 24.3) ÷ 3 = 24.2 cm³ Mark: Correct identification of concordant results and calculation (1 mark) Note: Rough trial excluded as it's an outlier

(b) Moles of NaOH [1] Working: n = c × V = 0.100 × (25.0/1000) = 0.100 × 0.0250 Answer: 0.00250 mol Mark: Correct conversion and calculation (1 mark)

(c) Moles of HCl [1] Answer: 0.00250 mol (1:1 molar ratio from equation) Mark: Correct application of stoichiometry (1 mark)

6. Melting point comparison [3]

Answer:

• Sodium bromide has a giant ionic lattice structure with strong electrostatic forces between Na⁺ and Br⁻ ions (1 mark)
• Tetrabromomethane has discrete molecules held together by weak van der Waals forces (1 mark)
• Strong electrostatic forces require more energy to break than weak intermolecular forces, so NaBr has a higher melting point (1 mark)

7. Amphoteric properties [3]

(a) Definition [1] Answer: A substance that can act as both an acid and a base / can react with both acids and bases Mark: Must show dual nature (1 mark)

(b) Strong acid [1] Answer: Hydrochloric acid / HCl OR Sulfuric acid / H₂SO₄ OR Nitric acid / HNO₃ Mark: Any strong acid (1 mark)

(c) Strong alkali [1] Answer: Sodium hydroxide / NaOH OR Potassium hydroxide / KOH Mark: Any strong alkali (1 mark)

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Section C: Calculation and Analysis [5 marks]

8. Organic acid calculation [4]

(a) Moles of NaOH [1] Working: n = c × V = 0.150 × (21.5/1000) = 0.150 × 0.0215 Answer: 0.003225 mol = 3.23 × 10⁻³ mol Mark: Correct calculation (1 mark)

(b) Moles of acid in 25.0 cm³ [1] Answer: 0.003225 mol (1:1 ratio for monoprotic acid) Mark: Correct stoichiometry (1 mark)

(c) Moles of acid in 1.00 dm³ [1] Working: (0.003225 mol / 25.0 cm³) × 1000 cm³ Answer: 0.129 mol Mark: Correct scaling calculation (1 mark)

(d) Relative molecular mass [1] Working: Mr = mass ÷ moles = 6.30 g/dm³ ÷ 0.129 mol/dm³ Answer: 48.8 g/mol Mark: Correct use of Mr = mass/moles (1 mark)

9. Dot and cross diagram for NH₃ [1]

Answer:

    H
    |
H—N:
    |
    H

With N showing 5 valence electrons (3 shared in bonds, 1 lone pair) and each H showing 1 electron shared.

Mark: Correct representation of covalent bonds and lone pair (1 mark) Note: Accept dots and crosses or just electron pairs, must show lone pair on nitrogen