DSEE Chemistry Paper 2B 2018 — Past Paper & Online Quiz

1. 0 marks

Two solutions were prepared as follows: Solution U1: Prepared by dissolving 2.12 g of sodium carbonate (Na₂CO₃) in 250 cm³ of water Solution U2: Contains hydrochloric acid of unknown concentration You are to determine the concentration of U2 using titration with methyl orange as indicator. Instructions: • Fill the burette with U2 • Pipette 25.0 cm³ of U1 into a conical flask • Add 2–3 drops of methyl orange and titrate with U2 • Repeat until three concordant titres are obtained and calculate the average

(a) What was the colour change observed during the titration? 2 mk

(a) What was the colour change observed during the titration? 0 mk

(b) Write a balanced chemical equation and ionic equation for the reaction. 4 mk

(b) Write a balanced chemical equation and ionic equation for the reaction. 0 mk

(c) Calculate the concentration of solution U1 in mol/dm³. 5 mk

(c) Calculate the concentration of solution U1 in mol/dm³. 0 mk

(d) If the average titre is 25.0 cm³, calculate the number of moles of HCl used. 0 mk

(d) If the average titre is 25.0 cm³, calculate the number of moles of HCl used. 4 mk

(e) Determine the concentration of HCl in mol/dm³. 0 mk

(e) Determine the concentration of HCl in mol/dm³. 6 mk

(f) Convert your answer in (e) to g/dm³. (Molar mass of HCl = 36.5 g/mol) 4 mk

(f) Convert your answer in (e) to g/dm³. (Molar mass of HCl = 36.5 g/mol) 0 mk

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2. 0 marks

In a study of the effect of temperature on reaction rate, a student was given: Solution V1: 0.1 M potassium iodide Solution V2: 0.1 M hydrogen peroxide Solution V3: 1 M sulfuric acid Starch solution The student was instructed to mix 5 cm³ of each solution in a test tube, add two drops of starch and record the time taken for a blue-black colour to appear. This was repeated at temperatures 30°C to 70°C. Page 2 of 3

(a) What causes the blue-black colour in this experiment? 2 mk

(a) What causes the blue-black colour in this experiment? 0 mk

(b) Complete the table below: 0 mk

(b) Complete the table below: 5 mk

(c) Write the ionic equation for the reaction between hydrogen peroxide and iodide in acidic medium. 4 mk

(c) Write the ionic equation for the reaction between hydrogen peroxide and iodide in acidic medium. 0 mk

(d) What effect does increasing temperature have on the rate of this reaction? 0 mk

(d) What effect does increasing temperature have on the rate of this reaction? 2 mk

(e) What precaution must be taken when measuring time during this experiment? 2 mk

(e) What precaution must be taken when measuring time during this experiment? 0 mk

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3. 0 marks

A salt labeled Z is suspected to be ammonium chloride. Carry out the following tests to confirm the ions: Page 3 of 3

(a) Describe the appearance of salt Z. 0 mk

(b) Heat a small amount in a dry test tube and test the gas evolved with damp red and blue litmus. 0 mk

(c) Add a portion to water and test with sodium hydroxide. Warm gently and test the gas evolved. 0 mk

(d) Add silver nitrate solution followed by nitric acid to a fresh portion. 0 mk

(i) Record your observations and inferences in a clear table. 0 mk

(ii) Identify the cation and anion in salt Z. 0 mk

(iii) Write balanced equations for: – The reaction with NaOH – The reaction with AgNO₃ 0 mk

(iv) Suggest two physical properties of salt Z that help identify it before any chemical test. 0 mk

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Chemistry · Paper 2B · 2018

Chemistry · Paper 2B · 2018

Section A

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