KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(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
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Dry ammonia and dry oxygen were reacted as shown in the diagram below
a)What is the purpose of the glass wool?
b) What products would be formed if red hot platinum was introduced into a mixture of ammonia and oxygen?
ANSWERS
(a)The purpose of the glass wool. It spreads the oxygen evenly/increase surface area or enriches the air with oxygen.
(b)Forms NO, Nitrogen (II) Oxide and steam
Hydrogen chloride gas can be prepared by reacting sodium chloride with an acid.
(a) Write an equation for the reaction between sodium chloride and the acid. (b) Give two chemical properties of hydrogen chloride gas (c) State two uses of hydrogen chloride
5g of calcium carbonate was strongly heated to a constant mass. Calculate the mass of the solid residue formed (Ca=40 0; C= 12.0; 0= 16.0). (2 marks)
A boiling tube filled with chlorine water was inverted in a trough containing the same solution and the set-up left in sunlight for about 2 hours.
Ethene is prepared in the laboratory by dehydration of ethanol.
Calculate the mass of Zinc oxide that will just neutralize dilute nitric (V) acid containing 12.6 g of nitric (V) acid in water. (Zn = 65.0; O =16.0, H = 1.0, N = 14.0).
a) State the Boyles Law
b) A gas occupies 500cm3 at 27°C and 100,000 Pa, What will be its volume at O°C and 101325 Pa?
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) A solution contains 40.3 g of substance XOH per litre. 25M cm3 of this solution required 30.0cm3 of 0.3 M sulphuric(Vl) acid for complete neutralisation. (a) Calculate the number of moles of XOH that reacted. (½ mark) (b) Determine the relative atomic mass of X. (1½ marks)
A monomer has the following structure.
(a) Draw the structure of its polymer that contains three monomers. (1 mark)
(b) A sample of the polymer formed from the monomer has a molecular mass of 4992. Determine the number of monomers that formed the polymer (C= 12; H= 1.0). (2 marks)
(a) The set up below was used to prepare dry hydrogen chloride gas, and investigate its effect on heated iron filings.
(i). Name substance L
(ii) Name liquid M (iii) What will be observed in tube B? (iv) Write an equation for the reaction that occurs in tube B. (v) Why is the gas from tube B burnt? (b) (i) Explain the following observations: I) A white precipitate is formed when hydrogen chloride gas is passed through aqueous silver nitrate. II) Hydrogen chloride gas fumes in ammonia gas. (ii) State two uses of hydrogen chloride gas (c) The diagram below is a representation of an industrial process for the manufacture of a bleaching powder.
(i) Name substance Q.
(ii)When the bleaching powder is added to water during washing, a lot of soap is used. Explain
ANSWERS
(a) (i) Sodium chloride / potassium chloride /rock salt.
(ii) Concentrated sulphuric (VI) acid (iii) Grey solid turns green
(i) I The gas reacts with silver nitrate to form insoluble silver chloride
II Both gases form ammonium chloride which is white. (ii) To make hydrochloric acid. Manufacture of ammonium chloride. Manufacture of PVC. Making chloroethene /vinyl chloride
A gas jar full of chlorine water was inverted over water and allowed to stand for sometime
a)State and explain two observations made in the gas jar after some time.
b) Write the equation for the reaction between chlorine and hot concentrated potassium hydroxide
A student used the set up below to prepare a sample of nitrogen gas.
a) State the function of potassium hydroxide in the set up
b) Give a suitable metal M for use in the combustion tube c) Give a reason why the nitrogen gas obtained is not pure.
ANSWERS
(a) It absorbs carbon (IV) oxide present in the air.
(b) Copper /Cu(S) (c) It has rare noble gases which have not been removed / Argon.
An organic compound had the following composition 37.21% carbon, 7.75% hydrogen and the rest chlorine. Determine the molecular formula of the compound, given that
the molecular mass of the compound is 65. (C=12.0; H=1.0; CL=35.5)
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 set up below and answer the questions that follow
(a)Write an equation for the reaction between ammonia and copper (II) oxide.
(b) During the experiment, the colour of the contents in the water trough changed. State the colour change observed and give an explanation.
100cm3 of 0.005 M sulphuric (VI) acid were placed in a flask and a small quantity of anhydrous sodium carbonate added. The mixture was boiled to expel all the carbon (IV) oxide. 25cm3 of the resulting solution required 18cm3 of 0.1 M sodium hydroxide solution to neutralize it.
Calculate the mass of sodium carbonate added. (Na = 23.0; O=16.0; C=12.0)
Study the flow chart below and answer the questions t hat follow.
Identify Z and M.
Z……………………… M……………………
(a) Draw and name the isomers of butyne
(b) State one use of polystyrene.
100cm3 of a sample of ethane gas diffuses through a porous pot in 100 seconds. What is the molecular mass of gas Q if 1000 cm3 of the gas diffuses through the same porous not in 121 seconds under the same conditions? (C=12.0, H=1.0)
Dry ammonia gas was passed over heated lead (II) oxide and the product passed over anhydrous Copper (II) sulphate as shown in the diagram below.
State:
(a)Two observations made in the combustion tube. (b) The property of ammonia gas shown in this experiment
ANSWERS
(a)The anhydrous copper (II) Sulphate turns from white to blue.
A grey solid is formed/droplets of a colourless liquid condense at cool part (b)Reducing property.
(Fe - = 56.0,Cl = 35.5 and Molar gas volume at 298K is 24,000cm3
C) When hydrogen sulphide gas was passed through a solution of iron (III) chloride, the following observation were made:
a) Fraction distillation of liquid air usually produces nitrogen and oxygen as the major products.
(Boiling points nitrogen = - 1960C, oxygen = -1830C)
b) Study the flow chart below and answer the questions that follow.
(a) describes one method that can be used to distinguish between sodium sulphate and sodium hydrogen sulphate.
b) Describe how a pure sample of lead (II) sulphate can be prepared in the laboratory starting with lead metal c) Study the flow chart below and answer the questions that follow:
i) Write an equation for the reaction in:
I step II; II step IV ii) State the observation made in step III. Explain. iii) Name another substance that can be used in step V.
ANSWERS
(a)Test the acidity using a litmus pager. There will be no change on litmus when dipped into a solution of sodium sulphate . The litmus paper turns to red when dipped into a solution of sodium hydrogen sulphate .
OR Add a solid carbonate to each solution. No effervescence observed when the carbonate is added to a solution of sodium sulphate. Effervescence is observed when the carbonate is added to a solution of sodium hydrogen sulphate. (b)Add dilute nitric acid to lead to form a soluble salt, Pb(NO3)2, add a soluble salt, Na2SO4. Then dry the salt between filter papers . (c)(i) NH4 NO3 → N2O + 2H2O II 2Fe(OH)3(S) → Fe2O3(s) + 3H2O(l) (ii) The colour changes from pale green to brown . The iron (II) is oxidised to iron (III) chloride by hydrogen peroxide (iii) Carbon monoxide |
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