In an experiment to investigate the percentage of oxygen in air,200cm³ of air was passed over heated copper turning repeatedly until a constant volume of air remained.160 cm³ of air remained at the end of the experiment.

(i)Name one gas remaining in the 160 cm³ of air.(1 mk)

(ii)Determine the percentage of air used up during the experiment.(2 mks)

(iii)What observation would be made during the experiment.(1 mk)

(iv)Write a word equation for the reaction between copper and oxygen.(1 mk)

Name the best method to use to separate the following mixtures.(4 mks)

(i)Common salt and water.

(ii)Coloured dyes in ethanol.

(iii)Ammonium chloride and sodium chloride.

(iv)Ethanol and water.

Study the set up below and answer the questions that follow.

(a)Identify gas X.(1 mk)

(b)Name the method used to collect gas X and give the property of the gas that enables it to be collected using the method.(2 mks)

(c)Write a word equation for the reaction liberating gas X.(1 mk)

(d)Why is not advisable to use the following in this method of preparing hydrogen;

(i)Calcium and dilute sulphuric acid(1 mk)

(ii)Zinc and Nitric (V) acid.(1mk)

(e)What is the purpose of anhydrous calcium chloride in the U-tube?(1mk)

(f)Name another compound that could serve the same purpose as anhydrous calcium chloride.(1 mk)

When magnesium is burnt in air,it reacts with oxygen and nitrogen gas giving a white ash.Write two equations for the two reactions that take place.(2 mks)

The diagram below was used to investigate the action of water on calcium metal.

(a)Identify gas R.(1 mk)

(b)The remaining solution in the beaker changes red litmus paper to blue.What does this suggest about the resulting solution.(1 mk)

(c)Write a word equation for the reaction.(1 mk)

(d)What would be observed if Carbon(IV)oxide is bubbled through the solution.(1 mk)

7 .a) Name the particles that are found in an atom.(3 mks)

b)Atoms are said to be electrically neutral.Explain.(2 mks)

c)Element Q has 18 neutrons and a mass number of 34.

i)How many protons are present in element Q?(1 mk)

(ii)Write the electron arrangement of element Q.(1 mk)

(iii)To which period and group does Q belong?Explain your answer.(2 mks)

8.(a)In an experiment to investigate what happens when steam is passed over heated magnesium,wet sand or cotton wool soaked in water is heated first before heating magnesium.Why is it necessary?(1 mk)

(b) Write a word equation for the reaction between magnesium and steam.(1 mk)

(c)Write a word equation for the reaction between iron and steam.(1 mk)

9.(a)What is the chemical name of rust?(1 mk)

(b)A form one student in attempt to stop rusting put copper and magnesium in contact with iron as shown.

(i)The set ups were left outside for two weeks.Where did rusting occur?Explain.(2 mks)

(ii)Name the method used by the student to prevent rusting.(1mk)

(iii)How does painting prevent rusting?(1 mk)

10.State the use of the following apparatus as used in the laboratory.

(a)Pipe-clay triangle(1 mk)

(b)Desiccator(1 mk)

(c)Wire gauze(1 mk)

11.The diagram below represents a set up for the laboratory preparation of oxygen gas.

Name solid R.(1 mk)

(ii)Write a word equation for the reaction in the flask.(1 mk)

(iii)How can one test for oxygen gas?(2 mks)

(iv)Give two commercial uses of oxygen gas.(2 mks)

A student was supplied with a colourless liquid suspected to be water.

(i) Describe one test that could be carried out to show that the liquid was water.(2 mks)

(ii)How could it have been shown that the liquid was pure water?(1 mk)

When a student was stung by a stinging nettle plant,a teacher applied an aqueous solution of ammonia to the affected area of the skin and the student was relieved of pian.Explain.(2 mks)

A mixture of magnesium powder and lead (II)oxide will react vigorously when heated but no reaction occurs when a mixture of magnesium oxide and lead powder are heated.

(a)Explain the observations above.(2 mks)

(b)Write a word equation for the reaction between magnesium and lead(II) oxide.(1 mk)

(c)From (b) above,identify the;(i)oxidised substance.(1 mk)

(ii)oxidizing agent.(1 mk)

(iii)what name is given to such a reaction?(1 mk)

15.Classify the following as either physical or chemical changes.(5 mks)

Freezing of beer

(b)Rusting of iron

(c)Heating of glass until it melts

(d)Burning a candle.

(e)Heating copper(II)nitrate

CHEMISTRY FORM 2 OPENER EXAMS MARKING SCHEMES

MARKING SCHEME (70 mks)

(1) Solid carbon (iv) oxide ,iron (III) chloride

(ii) zinc oxide and nitric (v) acid

2.Nitrogen or inert gases

(ii) 200-160/200*100=40/200X100=20%

(iii) Brown copper turnings turned black copper(II) oxide

iv) copper +Oxygen ———> Copper (II) oxide

(3i) Simple distillation

ii) chromatography

iii) Sublimation

iv) Fractional distillation

4 a) Hydrogen

b) upward delivery/download displacement of air

Hydrogen gas is less denser than air

C) Zinc +dilute hydrochloric acid ———->zinc chloride +hydrogen gas

d I)Formation of an insoluble coating layer of calcium sulphate that prevents further reaction from taking place

(ii) Nitric (v) acid oxidises hydrogen gas formed to water

e) Acts as a drying agent
f) Concentrated sulphuric (vi) acid

5.Magnesium + Oxygen ——–>Magnesium Oxide

Magnesium + nitrogen ——–> Magnesium nitride

(6) Hydrogen gas

b) it is basic in nature

(d) A white precipitate will be formed.

a) Electrons

Protons

Neutrons

b)Atoms have equal number of protons and electrons.Protons are positively charged while electrons are negatively charged thus electrically neutral.

c)i)34-18=16

ii)2.8.6

iii)Period 3-has three occupied energy levels

Group VI-has 6 electrons in the outermost energy level

a)To generate steam

b)Magnesium + steam —–>Magnesium oxide + hydrogen gas

c)Iron + steam ———-> Tri-iron tetra oxide + hydrogen gas

9.a)Hydrated iron (III) oxide

b)(i)Set up(i).This is because iron is more reactive than copper hence iron reacted with water. and oxygen.

(ii)Sacrificial protection

(iii)Painting cuts off oxygen gas and moisture from coming into contact with iron metal.

10.a) To hold the crucible during heating

b)Used for drying or keeping substances free from moisture.

c)Used for even distribution of heat when heating substances in beakers or flasks.

11.i)Sodium peroxide

ii)Sodium peroxide + water ——–>sodium hydroxide + oxygen gas

iii) Using a glowing splint.Oxygen relights a glowing splint.

iv) Used in hospitals by patients with breathing difficulties.

Used by deep sea divers and high mountain climbers.

12) A liquid suspected to be water turns white anhydrous Copper (II) sulphate to blue hydrated copper (II) Sulphats turns blue Cobalt (II) chloride papper to pink

ii) The purity of water can be tested by checking whether it boils at 100 oC

13) The product from stinging nettle plant is acidic hence aqueous ammonia solution being basic neutralizes the acidic product

14) Magnesium is more reactive than lead hence has a higher affinity of oxygen.It reduces lead (II) oxide to lead.Lead is less reactive than Magnesium thus can not displace oxygen in Magnesium Oxide.

(b) Magnesium + lead (II) oxide ——- Magnesium Oxide + lead

c) Magnesium

(ii) Lead

(iii) Redox reaction

15a) Physical

(b) Chemical

(d) Chemical

(e) Chemical

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