Exam (elaborations)
chemistry
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Consider the diagram below. b c Name the regions labeled a, b, c. (3 marks) a Pale blue zone b Green blue zone c Almost colourless zone
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0799933531CHEMISTRY
Paper 1
Time: 2 hours
CHEMISTRY PAPER 1 MARKING SCHEME
Kenya Certificate of Secondary Education
CHEMISTRY
PAPER 1
M A R K I N G S C H E ME
1. Consider the diagram below.
a
b
c
Name the regions labeled a, b, c. (3 marks)
a Pale blue zone b Green blue zone c Almost colourless zone
2. Some moist iron wool was placed in a test tube and the tube was inverted and set up as
shown below.
, x cm
y cm
The apparatus was left for one week. The water level rose and iron wool turned red-brown.
(i) Write the chemical equation to show the rusting of iron. (1 mark)
4Fe(s) + 302(g) + xH2O 2Fe2O3 xH2O(s)
(ii) Write the expression for an approximate percentage. (1 mark)
(iii) State two similarities between rusting and combustion.
(a) Both use oxygen (1 mark)
(b) Oxides are formed (1 mark)
3. Paper chromatography is a method of separating colours or dyes.
What two properties should the components of a mixture have that would make the
separation possible. (2 marks)
• Solubility in the solvents
• Stickiness or absorbility
4. A student was asked to prepare Lead (II) chloride salt using the following ingredients; Nitric
acid, lead (II)oxide and hydrochloric acid. Using ionic equations only explain how the salt
can be prepared. (2 marks)
PbO(s) + 2H+(aq) Pb2+(aq) + H2O(l)
Pb2+(aq) + 2Cl─(aq) PbCl2(s)
5. The nitrates of the following metals were heated strongly and observation made accordingly.
The nitrate of metal P produced the metallic oxide, Nitrogen (IV) oxide and oxygen gas; and
that of metal Q produced the metallic nitrite and oxygen gas. The nitrate of R produced metal
R, Nitrogen (IV) oxide and oxygen gas. Arrange the metals in order of
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, reactivity beginning with the most reactive. (2
marks)
Q, P, R
6. A student added barium hydroxide drop wise into a beaker containing dilute sulphuric (VI)
acid.
y
C
A
B
Conc. of ions in solution x
a What is the significance of point B? (1 mark)
The end point.
b Explain why point B does not touch the x-axis? (1 mark)
The solution left behind is of a very weak electrolyte.
c Explain what happens between
(i) A and B (1 mark)
Barium ions and sulphate ions are being removed gradually until point B whan
they are completely removed.
(ii) B and C (1 mark)
Excess Barium and hydroxide ions are being introduced gradually as all the
sulphate and H+ ions have been used up.
7. In an experiment it was found that 40.0cm3 of 0.2M sodium hydroxide solution just
neutralized 0.2g of a dibasic acid Q. Calculate the relative molecular mass of acid Q.
(2 marks)
2NaOH + H2X Na2X(aq) + H2O(l)
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