KCSE 2014 Chemistry Paper 1 Questions with Marking Scheme

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KCSE 2014 Chemistry Paper 2 Questions with Marking Scheme

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QUESTIONS

Explain how the hotness of a Bunsen burner flame can be increased. (1 mark)
When dilute hydrochloric acid was reacted with solid B, a colourless gas which extinguished a burning splint was produced. When an aqueous solution of solid B was tested with blue litmus paper, the paper turned red/ pink.
1. Identify the anion present in solid B. (1 mark)
2. Write an ionic equation for the reaction between solid B and dilute hydrochloric acid. (1 mark)
Dry ammonia gas was passed over heated lead (II) oxide and the products passed over anhydrous copper (II) sulphate as shown in the diagram below.

State:
1. Two observations made in the combustion tube. (2 marks)
2. The property of ammonia gas shown in the experiment. (1 mark)
Starting with zinc sulphate solution, describe how a sample of zinc oxide can be obtained. (3 marks)
Explain how conduction of electricity takes place in the following:
1. Iron metal. (1 mark)
2. Molten lead (II) iodide (1 mark)
100 cm³ of a sample of ethane gas diffuses through a porous pot in 100 seconds. What is the molecular mass of gas Q if 100 cm³ of the gas diffuses through the same porous pot in 121 seconds under the same conditions? (3 marks)
(C = 12.0, H = 1.0)
1. Draw and name the isomers of butyne. (2 marks)
2. State one use of polystyrene. (1 mark)
Complete the nuclear reaction below:
(a) (1 mark)

(b) State two uses of radioisotopes in health. (2 marks)
The table below shows the relative molecular masses and boiling points of pentane and ethanoic acid.

Explain the large difference in boiling points between ethanoic acid and pentane. (2 marks)
One of the ores of copper has the formula, CuFeS₂.
1. Describe how iron in the ore is removed during extraction of copper metal. (1 mark)
2. State two environmental problems associated with extraction of copper metal. (2 marks)
Study the flow chart below and answer the questions that follow.

Identify Z and M. (2 marks)
Z
M
The table below shows the pH values of solutions A, B, C and D.

Solution A B C D

pH 2 7 11 14

Select solutions in which a sample of lead (II) hydroxide is likely to dissolve. Give reasons for each solution selected. (3 marks)
100 cm³ of 0.05M sulphuric (VI) acid were placed in a flask and a small quantity of anhydrous sodium carbonate added. The mixture was boiled to expel all the carbon (VI) oxide. 25 cm³ of the resulting solution required 18 cm³ of 0.1 M sodium hydroxide solution to neutralise it. Calculate the mass of sodium carbonate added. (Na = 23; O = 16.0; C = 12.0) (3 marks)
When 20 cm³ of 1 M sodium hydroxide was mixed with 20 cm³ of 1 M hydrochloric acid, the temperature rose by 6.7⁰C. Assuming the density of the solution is 1 g/cm³ and the specific heat of the solution is 4.2 Jg^-1 k^-1;
1. Calculate the molar heat of neutralization. (2 marks)
2. When the experiment was repeated with 1 M ethanoic acid, the temperature change was found to be lower than with 1 M hydrochloric acid. Explain. (1 mark)
Study the set-up below and answer the questions that follow.
1. Write an equation for the reaction between ammonia and copper (II) oxide. (1 mark)
2. During the experiment, the colour of the contents in the water trough changed. State the colour change observed and give an explanation. (2 marks)
A measuring cylinder fitted with moist steel wool was inverted in a trough of water as shown in the diagram below.
1. State and explain the observations made in:
  1. Moist steel wool after four days. (1 mark)
  2. Water level in the measuring cylinder after four days. (1 mark)
2. What would be the effect of the steel wool moistened with salty water? (1 mark)
In an experiment of rates of reaction, potassium carbonate was reacted with dilute sulphuric (VI) acid.
1. What would be the effect of an increase in the concentration of the acid in the rate of the reaction? (1 mark)
2. Explain why the rate of reaction is found to increase with temperature. (2 marks)
Use the part of the periodic table given below to answer the questions that follow. (Letters are not the actual symbols of the elements.)
1. Identify the element that forms giant covalent structures. (1 mark)
2. Identify one element that does not form compounds. (1 mark)
3. Write the formula for the nitride of M. (1 mark)
Draw a set-up that can be used to separate a mixture of sand and iodine. (3 marks)
In the contact process, during the production of sulphur (VI) oxide, a catalyst is used. Give two reasons why vanadium (V) oxide is preferred to platinum. (2 marks)
Given that the atomic number of Y is 13 and that of Z is 9:
1. Write the electronic arrangement of Y and Z; (1 mark)
2. Draw the dot (.) and cross (x) diagram for the compound formed by Y and Z. (1 mark)
The set up below was used to separate a mixture of methanol and propanol. Study it and answer the questions that follow.
1. State the function of X. (1 mark)
2. Which liquid will collect first in the beaker? Give a reason. (1 mark)
Study the flow chart below and answer the questions that follow.
1. Name the process in step I. (1 mark)
2. Identify the reagent in step II. (1 mark)
3. Give one use of ethane. (1 mark)
1. A student electrolysed dilute sodium chloride solution using inert carbon electodes.
  Name the products at: (2 marks)
  1. Anode;
  2. Cathode.
2. If the experiment was repeated using concentrated sodium chloride instead of dilute sodium chloride solution, write the half equation at the anode. (1 mark)
An organic compound had the following composition 37.21% carbon, 7.75% hydrogen and the rest chlorine. Determine the molecular compound of the formula mass of the compound is 65. (C = 12.0; H = 1.0; Cl = 35.5). (3 marks)
Cotton is a natural polymer. State one disadvantage and one advantage of this polymer. (2 marks)
1. Name a suitable solvent for extracting an indicator from flowers; (1 mark)
2. Give a reason why the indicator named in (a) above is used. (1 mark)
A student used the set up below to prepare a sample of nitrogen gas.
1. State the function of potassium hydroxide in the set up. (1 mark)
2. Give a suitable metal M for use in the combustion tube. (1 mark)
3. Give a reason why the nitrogen gas obtained is not pure. (1 mark)
1. What is meant by the term radical? (1 mark)
2. The table below contains atoms that form common radicals. Complete the table to show radicals formed from various atoms.
A gas full of chlorine water was inverted over water and allowed to stand for some time.
1. State and explain two observations made in the gas jar after some time. (2 marks)
2. Write the equation for the reaction between chlorine and a hot concentrated potassium hydroxide. (1 mark)

MARKING SCHEME

Increasing the size of the air hole/increase the amount of air/open air holes competely. (1)
1. HSO^-₃ (1)
2. HSO₃^-1aq) + H⁺(aq) → H₂O(l) + SO₂(g)
  or
  NaHSO₃(s) + H⁺(aq) → Na⁺(aq) + H₂O(l) + SO₂(g)
1. - The anhydrous copper (II) Sulphate turns from white to blue. (1)
  - A grey solid is formed/droplets of a colourless liquid condense at cool part.(1)
2. Reducing property.(1)
- Add soluble carbonate/Add soluble hydroxide. (1)
- Filter out the zinc carbonate/filter the zinc hydroxide. (1)
- Heat strongly the ZnCO₃ to decompose it to form ZnO/Heat strongly the Zn(OH)₂ to decompose it to form ZnO. (1)
  OR
- Heat to evaporate the water. (1)
- Heat ZnSO₄ solid to decompose (1) to form ZnO/yellow solid. (1)
1. delocalised electrons. (1)
2. ions in the melt. (1)
2. Used in packaging - cushions electronics in boxes/insulation/models/ceiling strips/ crates or binding. (1)
1. (1)
2. 1. Cobalt 60 is used to detect the activity of the thyroid gland. (1)
  2. To sterise equipment/treatment of cancer/radio active Na for disorders in blood circulation/Barium meal for ulcers/detect fractures in bones. (1)
The molecules of ethanoic acid interact through strong hydrogen bonding (1) forming a dimer while molecules of pentane have weak van der waals forces. (1)
NB/ Ethanoic acid has hydrogen bonds while pentane does not have.
1. Roast ore in air/heat in air. (1)
  2CuFeS₂(s) + 4O₂(g) → Cu₂S(s) + 2FeO(g) + 3SO₂(g)
2. - Acid rain that corrodes stone work on buildings/land gulleys/dust pollution. (1)
  - SO₂ when breathed in causes bronchitis/chlorosis in plants. (1)
Z is SO₂ / sulphur (iv) oxide. (1)
M is H₂SO₃/ sulphuric (iv) acid. (1)
- A (1) and D (1)
- A is acidic it will neutralise Pb(OH)₂(aq) to form salt and water, ( 1/2 )
- D is a strong base it will react with Pb (OH)₂(aq) to form a complex ion. ( 1/2 )
- Lead (II) hydroxide is amphoteric.
- Moles of NaOH 18 × 0.1 = 0.0018 (1/2)
  1000
  Moles of acid 18 × 0.1 × 1/2 = 0.0009 (1/2)
  1000
  Moles in 100 cm³
  18 × 0.1 × 1 100⁴²= 0.0036 moles
  1000 2 25
  0.0036 × 100 (1/2)
  25
  Ratio of acid : Carbonate
  1 : 1
  Original moles of acid = 100 × 0.05
  1000
  = 0.005 /0.53g (1/2)
  0.005 - 0.0036 = 0.0014 moles / 0.3816g (1/2)
  Mass of Na₂CO₃ = 0.0014 × 106/0.53 - 0.3816
  = 0.1484 g = 0.1484 g (1/2)
1. Total volume of solution = 40 cm³ / 40 g (1/2)
  ∆ H = 40 × 6.7 × 4.2 (1/2)
  = 1125.6/1000
  = 1.1256 KJ
  Moles of acid 20 × 1 = 0.02 moles 1125.6 (1/2)
  1000 0.02
  0.02 moles = = 0.1256 KJ
  1 mole = 1.1256 KJ (1/2) -56280j/mol(1/2)
  0.02
  = -56.28KJ/mol (1/2)
2. Some energy is used to ionise the weak acid first before it can neutralise. So not all energy is used in neutralisation. (1)
1. 3CuO(s) + 2NH₃(g) → 3Cu(s) + N₂(g) + 3H₂O(l) (1)
2. It changed purple (1)
  The excess ammonia makes solution basic which turns purple with universal indicator. (1)
1. 1. It turned brown /blue/violet/green. (1)
  2. The water level rose up the gas jar/occupy space left by reacted O₂. (1)
2. The brown colour would be more since the salt accelerates rusting/rust faster. (1)
1. Rate increases. (1)
2. Temperature increases the kinetic energy (1) of the particles increasing the number of collisions. (1)
1. N (1)
2. R (1)
3. M₃N₂ (1)
Vanadium (V) oxide is cheaper (1) and is not easily poisoned by impurities. (1)
Y = 2.8.3 Z = 2.7 (1)
1. Condensation of alcohol with higher boiling point so that it runs back to the flask as the alcohol with lower boiling point distills over. (1)
2. Methanol. (1) It has a lower boiling point due to the size of carbon chain when compared with propanol. (1)
1. Step 1 is neutralisation. (1)
2. Step II is soda lime/ mixture of Naoh and CaO. (1)
3. Fuel/making ethene/making hydrogen gas. (1)
1. Anode - Oxygen /O₂ (1)
  Cathode - Hydrogen / H₂ (1)
2. 2Cl⁻aq) → Cl₂(g) + 2e
Empirical formula C₂H₅Cl (1/2)
Empirical mass = 2 x 12 + 5 + 35.5 = 64.5
64.5n = 65
n = 65/64.5
n = 1 (1/2)
therefore: molecular formula = C₂H₅Cl (1/2)
Natural polymers are biodegradable (1) and are expensive. (1)
Affected by acids/Not easily recyled.
1. Acetone / ethanol / propanone / propanol. (1)
2. The solvent dissolves the organic compound indicator present in the flowers / it is an organic solvent. (1)
1. It absorbs carbon (IV) oxide present in the air. (1)
2. Copper /Cu(s) (1)
3. It has rare noble gases which have not been removed / Argon. (1)
1. A radical is a compound formed when elements combine to form ions / free unstable atoms or molecules / a group of free unstable atoms exist in a compound /group of atoms with a common charge. (1)
1. A colourless gas is formed /chlorine water decompose to give oxygen (1/2)
  The colour of solution changes from green to colourless / chlorine water becomes hydrochloric acid. (1/2)
  The level of solution in the gas jar drops oxgen formed occupies space pushing water downwards. (1/2)
  (choose any 2)
2. 6KOH(aq) + 3Cl₂(g) → KClO₃(aq) + 5KCl(aq) + 3H₂O(l) (1)