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Secondary 3 Chemistry Semestral Assessment 2 (End of Year) Paper 1

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TuitionGoWhere Practice Paper - Chemistry Secondary 3

TuitionGoWhere Secondary School (AI)

Subject: Chemistry
Level: Secondary 3 (Express)
Paper: SA2 Practice Paper (Version 1 of 5)
Duration: 1 hour 15 minutes
Total Marks: 50

Name: ________________________
Class: ________________________
Date: ________________________

Instructions to Candidates

Write your name, class, and date in the spaces provided.
Answer all questions.
Write your answers in the spaces provided in this booklet.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a calculator.
A copy of the Periodic Table is printed on page 12 (not included in this digital version, assume standard data).

Section A: Structured Questions [40 marks]

Answer all questions in this section.

1. Calcium oxide is commonly used in agriculture to treat acidic soil.
(a) State the chemical formula of calcium oxide. [1]
........................................................................................................................................

(b) Explain, with the aid of a chemical equation, how calcium oxide increases the pH of the soil. [2]
........................................................................................................................................
........................................................................................................................................
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2. A student investigates the reaction between dilute sulfuric acid and excess zinc granules.
(a) Describe the observations when the zinc is added to the acid. [2]
........................................................................................................................................
........................................................................................................................................

(b) The student repeats the experiment using the same mass of zinc powder instead of granules.
State and explain the effect on the initial rate of reaction. [2]
........................................................................................................................................
........................................................................................................................................

3. Ammonium nitrate is a salt used as a fertiliser. It can be prepared in the laboratory by reacting aqueous ammonia with dilute nitric acid.
(a) Write a balanced chemical equation for this reaction, including state symbols. [2]
........................................................................................................................................

(b) Why is titration used to prepare ammonium nitrate, rather than the excess base method? [1]
........................................................................................................................................

(c) Describe how you would obtain pure, dry crystals of ammonium nitrate from the resulting solution. [3]
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4. Substance X is an oxide of a metal. It reacts with both hydrochloric acid and aqueous sodium hydroxide.
(a) What term is used to describe oxides that react with both acids and bases? [1]
........................................................................................................................................

(b) Name one metal whose oxide exhibits this property. [1]
........................................................................................................................................

(c) Write a balanced equation for the reaction of this metal oxide with hydrochloric acid. [2]
........................................................................................................................................

5. The table below shows the pH values of four different solutions, A, B, C, and D.

Solution	pH
A	1.0
B	5.5
C	13.0
D	7.0

(a) Which solution is strongly alkaline? [1]
........................................................................................................................................

(b) Which solution could be a sample of rainwater affected by acid rain? [1]
........................................................................................................................................

(c) Solution A is ethanoic acid ( $CH_3COOH$ ) and Solution B is hydrochloric acid ( $HCl$ ). Both have the same concentration ( $0.1 \text{ mol/dm}^3$ ). Explain why their pH values are different. [2]
........................................................................................................................................
........................................................................................................................................

6. Barium sulfate is an insoluble salt.
(a) Name two suitable aqueous solutions that can be mixed to prepare a precipitate of barium sulfate. [2]

........................................................................................................................
........................................................................................................................

(b) Write the ionic equation for this precipitation reaction, including state symbols. [2]
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(c) Describe the steps required to obtain a pure, dry sample of barium sulfate from the reaction mixture. [3]
........................................................................................................................................
........................................................................................................................................
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7. A student performs a titration to determine the concentration of a solution of sodium hydroxide.
$25.0 \text{ cm}^3$ of sodium hydroxide solution is pipetted into a conical flask. Phenolphthalein indicator is added. The solution is titrated against $0.10 \text{ mol/dm}^3$ sulfuric acid.
The equation for the reaction is:
$2NaOH(aq) + H_2SO_4(aq) \rightarrow Na_2SO_4(aq) + 2H_2O(l)$

The following burette readings were recorded:

Titration	Rough	1	2	3
Final reading / $\text{cm}^3$	24.50	23.80	47.90	24.10
Initial reading / $\text{cm}^3$	0.00	0.00	23.80	0.00
Volume used / $\text{cm}^3$	24.50	23.80	24.10	24.10

(a) Identify the concordant results and calculate the average volume of sulfuric acid used. [2]
Concordant results: ............................................................................................
Average volume: ............................................................................................ $\text{cm}^3$

(b) Calculate the number of moles of sulfuric acid in the average volume. [1]
........................................................................................................................................

(c) Determine the number of moles of sodium hydroxide present in the $25.0 \text{ cm}^3$ sample. [1]
........................................................................................................................................

(d) Calculate the concentration of the sodium hydroxide solution in $\text{mol/dm}^3$ . [2]
........................................................................................................................................

8. Copper(II) carbonate reacts with dilute hydrochloric acid.
(a) Write a balanced chemical equation for this reaction. [2]
........................................................................................................................................

(b) A student wants to prepare copper(II) chloride crystals. Explain why the student adds excess copper(II) carbonate to the acid. [1]
........................................................................................................................................

(c) How does the student know when the reaction is complete? [1]
........................................................................................................................................

9. Magnesium reacts with steam to form magnesium oxide and hydrogen gas.
(a) Write a balanced chemical equation for this reaction. [2]
........................................................................................................................................

(b) Describe a chemical test for hydrogen gas, stating the positive result. [2]
Test: ....................................................................................................................
Result: ..................................................................................................................

10. Potassium nitrate ( $KNO_3$ ) and lead(II) chloride ( $PbCl_2$ ) are both salts.
(a) State whether each salt is soluble or insoluble in water. [2]
Potassium nitrate: ..............................................................................................
Lead(II) chloride: ..............................................................................................

(b) Describe a method to prepare a dry sample of lead(II) chloride from solid lead(II) nitrate and solid sodium chloride. [4]
........................................................................................................................................
........................................................................................................................................
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Section B: Free Response Questions [10 marks]

Answer all questions in this section.

11. Sulfuric acid is a strong diprotic acid. Ethanoic acid is a weak monoprotic acid.
(a) Define the term strong acid. [1]
........................................................................................................................................

(b) Explain why a $0.1 \text{ mol/dm}^3$ solution of sulfuric acid has a lower pH than a $0.1 \text{ mol/dm}^3$ solution of ethanoic acid. [2]
........................................................................................................................................
........................................................................................................................................

(c) Both acids react with magnesium ribbon.
(i) State one similarity in the observations. [1]
........................................................................................................................................

(ii) State one difference in the rate of reaction and explain it in terms of particle collision. [2]
........................................................................................................................................
........................................................................................................................................

(d) Suggest a method, other than measuring pH or rate of reaction, to distinguish between equal concentrations of sulfuric acid and ethanoic acid in the laboratory. [2]
........................................................................................................................................
........................................................................................................................................

(e) Sulfuric acid is used in car batteries. State one safety precaution when handling sulfuric acid and explain why it is necessary. [2]
Precaution: ..........................................................................................................
Reason: ................................................................................................................

End of Paper

Answers

TuitionGoWhere Practice Paper - Chemistry Secondary 3 (SA2 Version 1)

Answer Key and Marking Scheme

Section A: Structured Questions

1.
(a) $CaO$ [1]
(b) Calcium oxide is a basic oxide. It reacts with acids in the soil (neutralisation). [1]
Equation: $CaO(s) + 2H^+(aq) \rightarrow Ca^{2+}(aq) + H_2O(l)$ OR $CaO + H_2SO_4 \rightarrow CaSO_4 + H_2O$ [1]
(Note: Accept equation with specific soil acid or generic $H^+$ )

2.
(a) Effervescence / Bubbles of gas produced. [1]
Zinc solid disappears / dissolves. [1]
(b) Rate increases. [1]
Powder has a larger surface area than granules, leading to more frequent effective collisions. [1]

3.
(a) $NH_3(aq) + HNO_3(aq) \rightarrow NH_4NO_3(aq)$ [1 for formulae, 1 for balancing/states]
(Note: State symbols required for full marks in strict marking, but often 1 mark for correct equation)
(b) Both ammonia and nitric acid are soluble/reactants are solutions; there is no insoluble excess to filter off. Titration allows exact neutralisation. [1]
(c) 1. Perform titration to find exact volume needed (using indicator). [1]
2. Repeat without indicator using exact volumes. [1]
3. Heat solution to saturation point/crystallisation point, then cool to crystallise. Filter and dry between filter papers. [1]

4.
(a) Amphoteric [1]
(b) Aluminium (or Zinc or Lead) [1]
(c) $Al_2O_3(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2O(l)$ [2]
(1 for correct formulae, 1 for balancing)

5.
(a) C [1]
(b) B [1]
(c) Hydrochloric acid is a strong acid and ionises completely in water, producing a high concentration of $H^+$ ions. [1]
Ethanoic acid is a weak acid and ionises partially in water, producing a lower concentration of $H^+$ ions. [1]

6.
(a) Barium chloride (or barium nitrate) AND Sodium sulfate (or potassium sulfate/magnesium sulfate). [2]
(Must be soluble barium salt and soluble sulfate)
(b) $Ba^{2+}(aq) + SO_4^{2-}(aq) \rightarrow BaSO_4(s)$ [2]
(1 for correct ions, 1 for state symbols)
(c) 1. Filter the mixture to collect the residue. [1]
2. Wash the residue with distilled water to remove soluble impurities. [1]
3. Dry the residue in an oven or between filter papers. [1]

7.
(a) Concordant results: Titration 2 and 3 (24.10 and 24.10). [1]
(Note: Titration 1 is 23.80, which is >0.10 cm³ different from 24.10, so it is not concordant with 2 and 3. Rough is ignored.)
Average volume: $\frac{24.10 + 24.10}{2} = 24.10 \text{ cm}^3$ [1]
(b) Moles of $H_2SO_4 = \frac{24.10}{1000} \times 0.10 = 0.00241 \text{ mol}$ [1]
(c) From equation, ratio $NaOH : H_2SO_4$ is $2:1$ .
Moles of $NaOH = 2 \times 0.00241 = 0.00482 \text{ mol}$ [1]
(d) Concentration of $NaOH = \frac{0.00482}{25.0/1000} = \frac{0.00482}{0.025} = 0.1928 \text{ mol/dm}^3$ [2]
(1 for calculation, 1 for unit/answer. Accept 0.193)

8.
(a) $CuCO_3(s) + 2HCl(aq) \rightarrow CuCl_2(aq) + H_2O(l) + CO_2(g)$ [2]
(1 for correct products, 1 for balancing)
(b) To ensure all the acid is reacted/neutralised. [1]
(c) When there is excess solid copper(II) carbonate remaining / effervescence stops. [1]

9.
(a) $Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)$ [2]
(1 for correct formulae, 1 for balancing. State symbols important for steam)
(b) Test: Insert a lighted splint into the gas. [1]
Result: Produces a 'pop' sound. [1]

10.
(a) Potassium nitrate: Soluble [1]
Lead(II) chloride: Insoluble [1]
(b) 1. Dissolve lead(II) nitrate in distilled water. [1]
2. Dissolve sodium chloride in distilled water. [1]
3. Mix the two solutions together. A white precipitate forms. [1]
4. Filter, wash with distilled water, and dry the precipitate. [1]

Section B: Free Response Questions

11.
(a) A strong acid is an acid that ionises/dissociates completely in water. [1]
(b) Sulfuric acid produces a higher concentration of hydrogen ions ( $H^+$ ) because it ionises completely. [1]
Ethanoic acid produces a lower concentration of hydrogen ions because it ionises only partially. [1]
(pH is a measure of $H^+$ concentration; higher $[H^+]$ means lower pH)
(c) (i) Effervescence / bubbles produced / solid dissolves. [1]
(ii) Sulfuric acid reacts faster. [1]
Because the concentration of $H^+$ ions is higher in sulfuric acid, leading to a higher frequency of effective collisions with magnesium atoms. [1]
(d) Measure the electrical conductivity. [1]
Sulfuric acid will have higher conductivity due to higher ion concentration. [1]
(Alternative: Add magnesium carbonate and measure volume of gas produced in a fixed time)
(e) Wear safety goggles/gloves. [1]
Sulfuric acid is corrosive and can cause severe burns to skin/eyes. [1]