KCSE 2016 Chemistry Paper 1 – Questions and Answers

No. 1. A student investigated the effect of an electric current by passing it through some substances. The student used inert electrodes, and connected a bulb to the circuit. The table below shows the substances used and their states.

(a) In which experiment did the bulb not light? (1 mark)

  • 1 and 3

(b) Explain your answer in (a) above. (2 marks)

  • In 1 ions K2CO3 are held rigidly within the crystal cannot move (no mobile ions) In 3 sugar exist as molecule hence no mobile ions.

No.2. An alknal has the following composition by mass: hydrogen 13.5%, oxygen 21.6% and carbon 64.9%

(a) Determine the empirical formula of the alcohol (C=12.0; H=1.0’ 0=16.0). (2mks)

  • [E.F.= C4H9OH]

(b) Given that empirical formula and the molecular formula of the alkanol are the same, draw the structure of the alkonol


No. 3. The figure below shows an energy cycle.

(a) Give the name of the enthalpy change ∆H1.  (1 mark)

  • Enthalpy of formation of hydrogen peroxide or enthalpy of formation

(b) Determine the value of ∆H3.(2 marks)

  • ∆H1 + ∆H3 = ∆H2 ∆H2 = ∆H2 – ∆H1
  • = – 285.8 – (-187.8) = 187.8 – 285.8 = – 98 kJmol-1

4. The set up below was used to investigate the reaction between dry hydrogen gas and copper

Reaction between hydrogen and copper

(a) Name substance A. (1 mark)

  • Fused anhydrous calcium chloride
  • Cao: fused CaCl2

(b) State the observation made in the combustion tube. (1 mark)

  • Black CuO changes to brown Cu metal
  • Formation of colourless liquid on the cooler parts of the combustion tube.

(C) Explain the observation stated in (b) above. (1 mark)

  • Copper (II) oxide is reduced by hydrogen to copper metal while hydrogen is oxidized to water /CuO reduced to Cu /H2 Oxidized to H2O

No. 5. Starting with sodium metal, describe how a sample of crystals of sodium hydrogen carbonate may be prepared. (3 marks)

  • React sodium with water to get sodium hydroxide. Bubble into this solution excess carbon (IV) oxide to get sodium hydrogen carbonate

No. 6. Ammonium ion has the following structure

Label on the structure:

(a) covalent bond;

(b) coordinate (dative) bond.

 

No. 7. When 8.53g of sodium nitrate were heated in an open test-tube, the mass of oxygen gas produced was 0.83 g . Given the equation of the reaction as 2NaNO 3 (s) -> 2NaNO 2 (s) + O 2 (g)

Calculate the percentage of sodium nitrate that was converted to sodium nitrite. (Na = 23.0, N = 14.0, O = 16.0) (3 marks)

Mole Concept Calculations

No.8. Aluminium is both malleable and ductile.

(a) What is meant by?

(i)  Malleable:                                      (1 mark)

  • Can be hammered into sheets.

(ii)Ductile                (1 mark)

  • Can be drawn into wires.

(b)State One use of aluminium based on:

(i) malleability                    (½ marks)

  • Making of sufurias/ motor vehicle parts/ aeroplane parts,window / door flames, cups, plates, packaging materials, pans, making sheets/ roof.

(ii)ductility            (½ marks)

  • electricity cables/ wires.

No. 9. The diagram below represents the set-up that was used to prepare and collect hydrogen chloride gas in the laboratory.

State the purpose of concentrated sulphuric (VI) acid in the wash bottle. (1 mark)

  • It is a drying agent.

Write an equation for the reaction between dry hydrogen chloride gas and heated iron. (1 mark)

  • Fe(s) + 2HCI(g)           FeCI2(s) +H2(g)

No. 10. Iron (III) oxide was found to be contaminated with copper (II) sulphate. Describe how a pure sample of iron (III) oxide can be obtained. (3 marks)

  • Add water to dissolve CUSO4, Fe2O3 doesn’t dissolve
  • Filter out the undissolved Fe2O3
  • Wash the residue with plenty of water ro remove traces of the filtrate.
  • Dry the residue between the filter papers

No.11.a) Complete the nuclear equation below: (1 mark)


(b) The half-life of   I is 8 days.

Determine the mass of 131I remaining if 50 grammes decayed for 40 days (1 mark)

(c) Give one harmful effect of radioisotopes.   (1 mark)
  • Instant / cause death
  • Cause cancer
  • Cause gene mutation

No. 12. During an experiment, chlorine gas was bubbled into a solution of potassium iodide.

(a) State the observations made.       (1 mark)

  • Solution turned from colourless to dark brown
  • Greenish yellow / pale green colour of Cl2 disappears
  • Brown solution / black solid is deposited

(b)Using an ionic equation, explain why the reaction is redox. (2 marks)

  • Cl2 (aq) +2I (aq) → I2 (aq)+2CI (aq)
  • Explanation; Iodine oxidation state changes from -1 to 0 hence oxidation

while Cl2 0.5 changes from 0 to -1 hence reduction / increase is ON and decrease is ON or movement of electrons Cl2 gains e’s where lose

No.13.(a) Draw the structure of compound N formed in the following reaction.

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