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Chemistry Form 1 Term 1 2021 Exam Set 1

Chemistry Form 1 Term 1 2021 Exam Set 1

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Question 1

Name three frequently abused drugs
Answer
Tobacco, alcohol, bhang, and khat
Question 2

State two long term effects of drug abuse.
Answer
Stress, depression, hallucination, addiction dependency, may be fatal (cause death).
Question 3

Define Chemistry:
Answer
Chemistry is the study of the structure, properties and compositions of matter and the changes that matter undergoes.
Question 4

Give an importance of studying Chemistry:
Answer
The knowledge of Chemistry helps in the following fields:
- Manufacture of drugs,food production, manufacture of cheaper fabrics such as nylon, manufacture of plastics such as PVC, manufacture of detergents, production of fuels for transport and domestic use.
Question 5

Give two reasons why most laboratory apparatus are made of glass.
Answer
- To allow easy observation as the experiment progresses / transparent
- Glasses do not easily react with chemicals.
Question 6

What is a flame?
Answer
- A flame is a mass of burning gases.
Question 7

The following diagrams represent the two types of flames produced by a bunsen burner.

(a) Identify the flames (a) and (b).
(b) Which type of the flames identified above is preferred for heating? Give a reason for your answer.
(c) Give four differences between the flames (a) and (b) above.
(d) Give two reasons why flames (a) and (b) above differ.
Answer
(a)
    a - non-luminous flame
    b - luminous flame.
(b) a- non-luminous flame. Produces much heat.
(c)
(a) non luminous flame (b) luminous flame
Has three zone Has four zones
Produces much heat and less light Produces much light and less heat
Short and steady Large and wavy
Roaring noisy flame Quiet flame
Produces soot No soot
(d) (a) - non-luminous flame is produced when the air hole is open while the luminous flame (b) is produced when the air hole is closed.
Question 8

A wooden splint was slipped through a region of a particular flame of the Bunsen burner in the laboratory. The splint was burnt as shown in the diagram below.

(a) Name the type of flame the splint was slipped through.
(b) Explain why the splint was burnt the way it is shown in the diagram.
Answer
(a) Non-luminous flame.
(b) The inner part has unburnt gases hence not hot while the outer part has completely burnt gases and is therefore hotter.
Question 9

After use, the non-luminous flame should be put off or adjusted to luminous flame. Explain.
Answer
- To preserve the gases, to avoid fire accidents because non-luminous flame is not easy to see .
Question 10

Putting off flames is one of the laboratory safety rules. State four other rules.
Answer
- Chemicals already used should be disposed off immediately to avoid contamination
- If a chemical gets into your skin or mouth, rinse it immediately with a lot of clean water
- Always extinguish flames that are not in use to avoid accidents and to minimize fuel wastage
- Never taste or eat anything in the laboratory to avoid poisoning
- Label all the chemicals you are using to avoid confusion.
Question 11

What is a mixture?
Answer
- A mixture is a physical combination of two or more substances which can be separated by physical means.
Question 12

State two physical means of separating a mixture.
Answer
- Winnowing, sieving, filtering, Evaporating, decanting, use of magnets.
Question 13

Makau, a form one student at Reki academy accidentally mixed sulphur and iron filings.
(a) Suggest an appropriate method of separation you would advice him to use to separate the mixture.
(b) Give a reason for the choice of your answer.
(c) Describe how he would use the method named in 5(a) above ton separate the sulphur and iron filings.
Answer
(a) Use of a magnet.
(b) Iron filings are magnetic while sulphur is not.
(c) Spread the mixture on a plain cardboard. Pass the magnet through the mixture. Iron filing are attracted to the magnet and are removed while sulphur is left on the cardboard
Question 14

Name two substances that sublime when heated.
Answer
- Anhydrous iron (iii) chloride
- Aluminium chloride
- Benzoic acid
- carbon (iv) oxide(dry ice)
- iodine
Question 15

Give two reasons why dry ice (solid carbon (IV) oxide) is preferred to be used in cold boxes by ice cream vendors over ordinary ice.
Answer
- It sublimes leaving no wetness
- It is a better coolant compared to ordinary ice
Question 16

A form one student wanted to separate and obtain iodine and sodium chloride (common table salt) from a mixture of the two. He set the experimental set up shown below:

The mixture was heated for some time and left to cool. On cooling, shiny black crystals and white crystals were observed on the surface of the watch glass and in the beaker respectively.
(a) Name:
    I. Shiny black crystals
    II. White crystals.
(b) What was the purpose of the cold water in the watch glass?
(c) Explain how the shiny black crystals on the surface of the watch glass is formed.
(d) What property of iodine makes it be collected on the watch glass as shown?
(e) Explain why it is possible to separate a mixture of iodine and sodium chloride.
Answer
(a)
    (i) Shiny-black crystals are iodine crystals
    (ii) White crystals are sodium chloride solid
(b) To cool and condense the iodine vapour to form iodine solid.
(c) When the mixture is heated, iodine sublimes into purple vapour. On reaching the surface of the watch glass, it is cooled and condensed into shiny black crystals of iodine.
(d) Iodine sublimes when heated.
(e) Iodine sublimes while sodium chloride does not.
Question 17

Define the following terms:
I. A saturated solution
II. Crystallization
Answer
(i) A saturated solution is a solution that has maximum solute and that cannot dissolve any more solute at a given temperature.

(ii) Crystallization is the process of obtaining salt crystals from a saturated solution by cooling.
Question 18

Describe how copper (II) sulphate crystals can be obtained from copper (II) sulphate solution.
Answer
Evaporate the solution to dryness. Allow the saturated solution to cool to form crystals.
Question 19

Give two industrial applications of crystallization as a method of separating soluble substances from their solutions.
Answer
- Extraction of salt from salty water.
- Extraction of sugar from sugar cane.
- Extraction of medicinal substances from plants.
- End of Questions -