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​These are chemistry questions and answers categorized according to topics, papers i.e. Paper 1 and 2, Levels i.e. form 1 to form 4, kcse year the examination was done and section A or B
Select topic/category to open topical questions from that particular option provided. ​Chemistry Topics
The apparatus shown below were used for the preparation of hydrogen sulphide gas in the laboratory13/10/2021 
The apparatus shown above were used for the preparation of hydrogen sulphide gas in the laboratory
a) Name;i) Substance V (1mk)
V is Dilute hydrochloric Acid
ii) Solid X (1mk)
W is Iron (ii) Sulphide
b) Write an equation for the preparation of hydrogen sulphide (1mk)
c) What property of the gas enables it to be collected by the method shown in the diagram? (1mk)
It is denser than air
d) What is the purpose of the water in the second flask? (1mk)
To absorb acid vapour (HCl)
e) What precaution should be taken when preparing the gas? (1mk)
The gas should be prepared in a fume chamber or in the open
f) Explain the observations made when dry hydrogen sulphide is exposed to wet Lead (II) acetate paper (2mks)
Black colour observed; black lead (ii) sulphide is formed.
g) State the observation that would be made when hydrogen sulphide gas is bubbled through acidified Potassium dichromate (VI) solution (1mk)
h) Explain why it is not advisable to dispose off hydrogen sulphide gas by burning (1mk)SO2 is formed causing acid rain a) Explain why sulphur is soluble in ethanol but hot in water (1mk)
b) Explain how a pure sample of sodium chloride can be obtained from a mixture of the two (1mk)
One of the allotrope s of sulphur is rhombic sulphur.
(a) Name the other allotrope of sulphur. (b) Draw a diagram to show the shape of the allotrope named in (a) above. (c) Write an equation for the reaction between concentrated sulphur(VI) acid and sulphur
ANSWERS
Hydrogen sulphide is a highly toxic and flammable gas. It is normally prepared in a fume chamber.
(a) Name two reagents that can be used to prepare hydrogen sulphide in the laboratory. (b) One of the uses of hydrogen sulphide is to produce sulphur as shown in the following equation: 2H2S(g) + S02 (g) -> 3S(s) + 2H20(1) Identify the reducing agent in this reaction and give a reason for your answer. (c) Other than production of sulphuric (VI) acid, state one commercial use of sulphur.
ANSWERS
(a)Iron (II) sulphide or conc sulphide / copper sulphide (Accp formula: Fes/ HCl)
Hydrochloric acid or lead (II) sulphide/ HNO3 (b)Hydrogen sulphide The sulphur changes from -2 to zero/ (it reduces SO2 to S) i.e. +4 to 0 / sulphur lost e’s in the H2S to form sulphur (c)Vulcanization of rubber Manufacture of sulphur drugs Manufacture of gun powder/ match sticks / explosives/ fungicides
The set up below can be used to generate a gas without heating. This occurs when substance M reacts with solid N.
a i) Complete the table below giving the names of substance M and solid N if the gasses generated are chlorine and sulphur (IV) oxide.
(ii) Complete the diagram above to show how a dry sample of sulphur (IV) oxide can be collected
(b) Describe two chemical methods that can be used to test the presence of sulphur (IV) oxide. (c) Other than the manufacture of sulphuric (VI) acid, state two uses of sulphur (IV) oxide.
ANSWERS
(b) Presence of SO2
- Use of acidified potassium dichromate (VI) which turns from orange to green. - Bubble gas through acidified potassium manganate (VII) which decolourises /changes i.e from purple to colourless. - Iron (III) sulphate solution - yellow/brown changes to green - Bromine water colour changes from yellow/brown / orange to colourless (c) - Fumigation - Bleaching agent - Preservative . - Disinfectant - Antioxidant
(a) One of the allotropes of sulphur is rhombic sulphur, name the other allotrope.
(b) Concentrated sulphuric (VI) acid reacts with ethanol and copper. State the property of the acid shown in each case. (i) Ethanol .................... (ii) Copper ....................
ANSWERS
(a) Monoclinic sulphur /Beta sulphur! Prismatic sulphur
(b) (i) Dehydrating property (ii) Oxidising property
Sulphur(IV) oxide is prepared in the laboratory using the set-up in Figure 3. Study it and answer the questions that follow.
(a) Identify substance F. (1 mark)
(b) Write an equation for the reaction that takes place in the flask. (1 mark) (c) State the purpose of liquid G. (I mark)
Expected Response
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.
ANSWERS
Study the flow chart below and answer the questions t hat follow.
Identify Z and M.
Z……………………… M……………………
ANSWERS
(a) The diagram below shows the frasch process used for extraction of sulphur
Use it to answer the question that follows 
(i) Identify X
(ii) Why is it necessary to use superheated water in this process (iii) State two physical properties of sulphur that makes it possible for it to be extracted by this method (b) The diagram below shows part of the process in the manufacture of sulphuric (VI) acid. Study it and answer the questions that follow 
(I) Write an equation for the formation of sulphur (IV) oxide from sulphur
(II) What is the role of concentrated sulphur (VI) acid in chamber A? (III) Name two catalysts that can be used in the catalytic chamber B. (IV) State two roles of the heat exchanger (c) Explain one way in which sulphur (IV) oxide is a pollutant (d).what observation will be made when a few drops of concentrated sulphuric (VI) acid are added to crystals of sugar? Explain your answer
ANSWERS
(a)(i)Hot compressed air
(ii)To melt the sulphur and maintain it in molten state (iii)low melting point of sulphur - insolubility of sulphur in water - less dense than water (b)(i)S + O2 → SO2 (ii)To dry the SO2 and air (iii)Vanadium (v) oxide and platinum or titanium (iv)it provides the reactants (SO2 and O2) with enough energy to react - it removes heat from the product hence preventing decomposition or conserves heat, or recycles heat or reduces cost of production. (c)- contributes to acid rain which corrodes buildings OR - causes aquatic solutions to be acidic hence affecting aquatic life etc. - poisonous/toxic (d)Turns black conc H2SO4 removes hydrogen and oxygen from the sugar molecule leaving only carbon which is black . Dehydration of sugar forms carbon which is black.
a) What would be observed if sulphur (IV) oxide is bubbled through acidified potassium manganate (VII)
(b) In an experiment, sulphur (IV) oxide was dissolved in water to form solution L. (i) What would be observed if a few drops of barium nitrate solution were immediately added to solution L? (ii) Write an ionic equation for the reaction that occurred between solution L and aqueous barium nitrate in (b) (i) above.
ANSWERS
When a sample of concentrated sulphuric acid was left in an open beaker in a room for two days, the volume was found to have increased slightly
Expected Answer
(a) Hygroscopy
(b) Drying of gases ║drying agent
When the oxide of element H was heated with powdered carbon the mixture glowed and carbon dioxide was formed. When the experiment was repeated using the oxide of element J, there was no apparent reaction.
Expected Answer
(a) Electrolysis of fused or molten oxide
(b) JCH║J, carbon, H
A certain matchstick head contains potassium chlorate and sulphure. On striking the two substances react to produce sulphure dioxide and potassium chloride. Explain the environmental effect of using such matches in large numbers.
Expected Answer
SO2 which is poisonous is released in the air. Acid rain which may cause corrosion will be formed |
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AuthorMaurice Atika is a teacher and a netprenuer. |
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