NAME: _________________________________________________ CLASS: 3

MIKUYU COMMUNITY DAY SECONDARY SCHOOL

2018/19 FORM THREE END OF YEAR EXAMINATIONS

CHEMISTRY
(85 marks)
July, 2019 Time Allowed: 2hrs.

Instruction: answer all questions in the spaces provided

SECTION A (65 Marks)
1 a. Define the term chemistry.
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b. State the difference between “accuracy” and “precision”.

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c. Figure 1 is a diagram of a container with molecular models in various positions. The

models are supposed to be at the centre of the container.

Using letters A, B and C, Identify the molecular models that have

i. good precision but poor accuracy.______________________ (1 mark)
ii. both poor precision and accuracy.___________________________________ (1 mark)
iii. both good precision and accuracy_______________________________ (1 mark).
2. The table below shows electron configuration and relative abundance of isotopes of an
element.

Isotope Electron configuration Relative

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 Abundance
X - 28 2,8,4 8/10
X - 29 2,8,4 1/10
X - 30 2,8,4 1/10
a. To which group of the periodic table does element X belong?
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b. Element X reacts with element Y whose valency is 2. Write the chemical formula of
the product.

(2 marks)

3. Sabriellium is a newly discovered metal element by form 2 leaners at Nkhotakota CDSS.

After taking a series of tests, they found that the element is very soft, and reacts vigorously
with water giving out a gas and a pop sound to a glowing splint. Its solution turns red
litmus paper to blue.

a. Suggest the family of this element. ____________________________________ (1 mark)

b. Would this element be found along the river? ___________________________ (1 mark)
c. Suggest a reason for your answer to question 12 b.
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d. suggest how you can keep Sabriellium in the laboratory.
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e. Give the name of the gas that was produced from the reaction.
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4. A hydrocarbon contains 85.7% carbon and 14.3 % hydrogen by mass. Write the
molecular formula of the hydrocarbon if its relative formula mas is 56.

(RAM: C=12, H=1)

(7 marks)

5. a Give any two examples of laboratory wastes.

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b. Give any two benefits of recycling wastes.
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c. Give two properties which can be used to identify the purity of a substance.
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6. a. Give any one use of electron configuration.
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b. Mention any two sources of nitrogen.
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c. Why is nitrogen gas inert at room temperature?
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d. Explain any one way in which the inertness of nitrogen is important?
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e. State one condition under which nitrogen can react.
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7. Why is burning of plastics not recommended as a method of disposal?
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8. a. Define the term chemical bond.
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b. State any one difference between ionic bonding and covalent bonding.
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d. Explain why a school bell is made up of metallic material but not rubber?
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9. a. Explain why ionic compounds require large amounts of heat to melt than covalent
compounds?
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10. a. Explain why argon gas is obtained before oxygen gas during separation of air into its
components?
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b. Describe how carbon dioxide is removed from air.
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11. a. Explain how burning of fuel causes global warming.
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12. Aqueous sodium hydroxide was added to various salt solutions as shown in the table.
Complete the table correctly by filling the missing information.

Cation in solution 3 drops In excess

Zn2+

Green precipitate

Ca2+

Insoluble precipitate

(8 marks)
13. Describe how you would test for the presence of sulphate ions in an unknown salt
compound.
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 SECTION B (20 MARKS)
14. With the aid of chemical equations, explain how ozone layer is depleted.

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15. A new brand of body lotion is causing skin rash unlike the old brand of the same
lotion.
With the aid of a well labelled diagram, describe an experiment that could be done to
isolate the pigment that is causing the skin rash.

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END OF QUESTION PAPER

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