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2007 ICSE Chemistry sample paper Question paper



Course: Plus II   University/board: ICSE





CHEMISTRY PAPER

(One and a half hours)

Answers to this paper must be written on the paper provided separately.
You will NOT be allowed to write during the first 15 minutes.
This time is to be spent in reading the question paper.
The time given at the head of this paper is the time allowed for writing the answers.
Section A is compulsory and attempts any four questions from Section B.
The intended marks for questions or parts of questions, are given in brackets [ ].

SECTION I

Answer all questions

Question 1
(a) From among the elements chlorine, nitrogen and sulphur select one element in each case,
to which the following descriptions could apply :
(i) the least reactive
Ans. Nitrogen is least reactive.
(ii) bleached moist blue litmus paper
Ans. Chlorine bleaches moist blue litmus paper.
(iii) obtained from the atmosphere
Ans. Nitrogen obtained from the atmosphere.
(iv) used in the vulcanisation of rubber
Ans. Sulphur is used in the vulcanisation of rubber.
(v) reacts with water
Ans. Chlorine reacts with water.
(vi) has the property of allotropy
Ans. Sulphur has the property of allotropy
(vii) burns in oxygen forming an acidic oxide
Ans. Sulphur burns in oxygen to give SO2 which is an acidic oxide.
(viii) prepared in the laboratory by an oxidation reaction.
Ans. Chlorine is prepared in the laboratory by an oxidation reaction.

(b) Name the gas evolved when the following mixtures are heated :
(i) Calcium hydroxide and ammonium chloride
Ans. NH3 gas
(ii) Sodium nitrate and ammonium chloride
Ans. N2 gas
(iii) Manganese oxide and concentrated hydrochloric acid.
Ans. Cl2 gas

(c) (i) A farmer's land appears to be lacking in nitrogen. State two different
ways in which the farmer could increase the amount of nitrogen in the
soil.
Ans. By supplying urea and ammonium nitrate.
(ii) During a thunderstorm, the rain water contains nitric acid. The nitric acid is formed as a result of three chemical reactions.
Describe (or write balanced chemical equations for ) these three reactions.
Ans. Electric
N2 + O2 2NO
Arc
2NO + O2 NO2

4NO2 + O2 + 2H2O 4HNO3

(d)(i) At 0oC and 760 mm Hg pressure, a gas occupies a volume of 100 cm3. The
Kelvin temperature (Absolute temperature) of the gas is increased by one-
fifth while the pressure is increased one and a half times. Calculate the final
volume of the gas.
Ans. P1 = 760 mm P2 = 760 + 1.5 x 760 = 2.5 x 760 mm

T1 = 0oC or 273 K T2 = 273 +(1) x 273 = 1.2 x 273 K
5
V1 = 100 cm3 V2 = ?

Apply gas equation to calculate the new volume,
P1V1= P2V2
T1 T2
Substituting the values in the above equation,
760 x 100= 2.5 x 760 x V2
273 1.2 x 273

or V2 = 48 cm3

(ii) Complete the following sentences :
" If two gases under the same conditions have the same number of
molecules then they must …………………. "
Ans. If two gases under the same conditions have the same number of
molecules then they must occupy same volume.
(iii) What volume of propane is burnt for every 100 cm3 of oxygen used in
the reaction C3H8 + 5O2 3CO2 + 4H2O? (Gas volumes measured under the same conditions) ?
Ans. C3H8 + 5O2 3CO2 + 4H2O
1 vol 5 vol 3 vol
5 cm3 oxygen is used to burn = 1 cm3 of propane
100 cm3 oxygen is used to burn = 20 cm3 of propane

(e) Answer the following questions about electroplating a copper-wave with
silver :
(i) What ions must be present in the electrolyte?
Ans. Ag+ ions
(ii) Of what substance must the anode be made?
Ans. Ag metal
(iii) What will be made the cathode?
Ans. Copper wire
(iv) What is the equation for the reaction which takes place at the cathode?
e
Ans. Ag+ Ag

(f) (i) Sodium hydroxide solution is added to solution A. A white precipitate
is formed which is insoluble in excess sodium hydroxide solution. What
is the metal ion present in solution A?
Ans. Ag + + OH- AgOH
2AgOH Ag2O + H2O
white ppt
Ag2O + NaOH Insoluble

(ii) When ammonium hydroxide is added to solution B, a pale blue
precipitate is formed. This pale blue precipitate dissolves in excess
ammonium hydroxide giving an inky blue solution. What is the cation
present is solution B? What is the probable colour of solution B?
Ans. The cation present in B is Cu2+
CuSO4 + 2NH4OH Cu(OH)2 + (NH4)2SO4
Pale blue
Cu(OH)2 + 4NH4OH [Cu(NH3)4] (OH)2 + 4H2O
Inky blue

The colour of solution B is blue.

(iii) When an ammonium salt is warmed with sodium hydroxide solution,
ammonia gas is evolved. State three ways in which you could identify
this gas.
Ans. It has a typical smell
It gives fumes with a rod dipped in HCL.
It turns turmeric paper brown.

(g) For each of the salts A, B, C and D, suggest a suitable method of
Preparation which relates to its description given below :
(i) A is a sodium salt.
Ans. Treatment of NaOH with a mineral acid.
(ii) B is an insoluble salt.
Ans. Treatment of Ba(NO3)2 or Pb(NO3)2 with H2SO4.
(iii) C is a soluble salt of copper.
Ans. Heating copper metal with conc. H2SO4.
(iv) D is a soluble salt of zinc.
(Do not describe the procedure for the preparation. Refer only to the
appropriate method)
Ans. Treating Zn with dil HCL or dil H2SO4.

(h) Define or explain the meaning of the following terms :
(i) Acid
Ans. An acid is a substance which gives H+ in the solution.
(ii) pH scale
Ans. pH is negative logarithm of H+ concentration.
(iii) Catalyst
Ans. Catalyst is a substance which speeds up the rate of a chemical reaction.
(iv) Electrolysis
Ans. On passing electric current through a solution of an electrolyte
(containing cations and anions), cations are deposited at the cathode
and the anions at the anode. This process is called electrolysis.


SECTION II

Question 2
(a) (i) What would you see when a crystal of CuSO4.5H2O is placed in
concentrated sulphuric acid? What is the reason for the observation?
Ans. Conc.H2SO4
CuSO4.5H2O CuSO4
-5H2O
Blue colour White
Conc. H2SO4 is a strong dehydrating agent. It absorbs the water molecules of crystallisation and leaves a
white powder of CuSO4.

(ii) Describe another way in which you could produce the same effect as absorbed in (a) (I)
Ans. The same effect could be produced by heating a crystal of blue copper sulphate CuSO4.5H2O
D
CuSO4.5H2O CuSO4
-5H2O
(Blue) (White)

(iii) What is the meaning of the term "Water of crystallisation"?
Ans. Water of crystallisation means water molecules which are attached to the molecule of a substance in its
crystals. It gives shape and colour to the crystal. e.g.
FeSO4.7H2O (Green)
Na2SO4.10H2O (white)

(b) (I) Name two other acids other than sulphuric acid which can be prepared by using sulphuric acid.
Ans. HCL and HNO3. These can be prepared as follows :
NACL + H2SO4 NaHSO4 + HCL
NaNO3 + H2SO4 NaHSO4 + HNO3

(ii) In using sulphuric acid to prepare the acids as mentioned in (b) (i), which property of sulphuric acid is used?
Ans. Non-volatile nature of H2SO4.

(C) Sulphuric acid can be used to prepare a number of gases in the laboratory. Write balanced equations for
reactions in which the following gases are obtained using dilute sulphuric acid as one of the reactants :
(i) hydrogen
Ans. dil
Zn + H2SO4 ZnSO4 + H2

(ii) carbon dioxide
Ans. 2NaHCO3 + H2SO4 Na2SO4 + 2CO2 + 2H2O

Question 3
(a) Sodium chloride
A B
Sodium hydroxide solutions Sodium hydroxide solutions
Sodium Chlorine Sodium chlorate hypochlorite
C
Iron (III)
chloride
Parts (a) (I) -(iv) refer to the above diagram :
(j) For the conversion A, name two other reactants required.
Ans. MnO2 and conc. H2SO4
NaCL + H2SO4 NaHSO4 + HCL
MnO2 + 2HCL + H2SO4 MnSO4 + 2H2O + Cl2

(ii) How can conversion B be brought about?
Ans. 2Na + CL2 2NaCL

(iii) Write a balanced equation for conversion C, if it is brought about by direct combination.
Ans. 2Fe + 3CL2 2FeCL3

(iv) State the conditions necessary for the conversions D and E.
Ans. NaOH
Conversion of D viz Cl2 Sodium hypochlorite takes place in cold.
. NaOH
For the conversion E viz Cl2 Sodium chlorate heating is required.

(b) (i) How does sodium hudroxide solution act in distinguishing iron (II) chloride solution from iron (III) chloride
solution?
Ans. Iron (II) chloride gives a green precipitate of Iron (II) hydroxide on adding sodium hydroxide. Iron (III)
chloride gives a reddish brown precipitate of Iron (III) hydroxide on adding sodium hydroxide.
FeCl2 + 2NaOH Fe(OH)2 + 2NaCL
Green
FeCL3 + 3NaOH Fe(OH)3 + 3NaCL
Brown

(ii) What is the chemical process involved in using moist chlorine as a bleaching agent?
Ans. Using moist chlorine as a bleaching agent involves oxidation
CL2 + H2O 2HCL + [O]
[Coloured substance] + [O] [Colourless substance]

(iii) Why does bleaching powder smell of chlorine?
Ans. Bleaching powder smell of chlorine due to the following reaction :
moisture
CaOCL2 + H2O Ca(OH)2 + CL2
In air

Question 4
(a) (I) Iron pyrites has the formula FeS2. What mass of sulphur is contained in 30 g of pyrites?
Ans. FeS2 = 2S
(56 + 64 = 120) 64
120 g pyrites contain = 64 g S
64
30 g pyrites contain = 120x 30 = 16 g


(ii) When roasted, iron pyrites gives sulphur dioxide according to the following equation :
4FeS2 + 11O2 2Fe2O3 + 8SO2
What volume of sulphur dioxide (at STP) would be liberated by roasting 30 g of pyrites?
(S = 32; Fe = 56; molar volume of a gas is 22.4 litres at STP)
Ans. 4FeS2 + 11O2 2Fe2O3 + 8SO2
4 x 120 8 X 22.4 litre
= 480 g
480 g pyrites liberate = 8 x 22.4 litre SO2

30 g pyrites liberate =8 x 22.4 x 30 = 11.2 litre
480

(b) (I) Write balanced equations for the three chemical reactions that take place during the
conversion of sulphur dioxide to sulphuric acid in the Contact process.
Ans. S + O2 SO2
2SO2 + O2 2SO3
SO3 + H2SO4 H2S2O7
Oleum
H2S2O7 + H2O 2H2SO4

(ii) Name the catalyst used in the Contact Process.
Ans. Platinised asbestos or V2O5

(iii) Name another ore which on roasting gives sulphur dioxide.
Ans. Zinc blende or ZnS
2ZnS + 3O2 2ZnO + 2SO2

Question 5
(a) Copy and complete the following equations :
(i) Mg3N2 + 6H2O
Ans. Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3

(ii) 2NH3 + 3CuO
Ans. 2NH3 + 3CuO 3Cu + 3H2O + N2

(iii) 8NH3+ 3CL2
Ans. 8NH3 + 3CL2 6NH4CL + N2

(iv) 4NH3 + 5O2
Ans. 4NH3 + 5O2 4NO + 6H2O

(b) (I) How would you obtain the compound magnesium nitride?
Ans. By burning magnesium in the atmosphere of nitrogen
3Mg + N2 Mg3N2

(ii) What property of ammonia is illustrated by reaction (a) (ii) above?
Ans. Oxidation of NH3

(iii) What important industrial process starts with reaction (a) (iv) above? Name the catalyst
used.
Ans. Ostwald process for the manufacture of nitric acid. Catalyst used is platinum gauze.

(c) During laboratory preparation how is ammonia dried and collected?
Ans. Ammonia is dried by passing it through quick lime (CaO) and is collected by downward
displacement of air.

Question 6
(a) (i) The pH value of pure water is 7. Compare the pH values of sulphur dioxide solution and
ammonia solution with that of pure water.
Ans. Sulphur dioxide is a non-metal oxide, such oxides are acidic with pH less than 7.
Ammonia solution is alkaline with pH more than 7.

(ii) Why is it necessary to add acid to water before proceeding with the electroysis of `water'?
Ans. This helps in the ionisation of H2O

H2O H+ + OH-


(b) Name :
(i) two bases which are not alkalies.
Ans. NH4OH, Mg(OH)2

(ii) a normal salt and an acid salt of the same acid.
Ans. Na2SO4, NaHSO4

(iii) a salt insoluble in cold water but soluble in hot water.
Ans. PbCL2

Question 7
The following questions refer to the extraction of aluminium and iron from their ores :
(a) Name the principal ore from which (i) iron and (ii) aluminium are extracted.
Ans. (i) Haematite Fe2O3
(ii) Bauxite Al2O3

(b) What is the most important chemical process in the extraction of any metal? State how
this essential step is carried out in the extraction of (I) iron, (ii) aluminium.
Ans. Reduction of the oxide
In case of iron
Fe2O3 + 3CO 2Fe + 3CO2
AL2O3 cannot be easily reduced, hence it is subjected to electrolysis. Aluminium is
collected at the cathode.

(c) Iron and aluminium ores both, contain impurities. Explain briefly how these impurities
are removed in each case.
Ans. Iron ore contains impurities of silica and sand. These are removed by magnetic
separation. Bauxite and aluminium ore contains impurities of FeO and SiO2.
Bauxite containing FeO is calcinated at high temperature when FeO is oxidised to
Fe2O3. Calcinated ore is then treated with NaOH when AL2O3 is converted into
soluble NaALO2. Fe2O3 can thus be filtered off. Bauxite containing SiO2 is mixed
with coke and heated to 1000oC in an atmosphere of N2. Silica is reduced to Si which
volatilises at the temperature of reaction. Aluminium oxide is converted into ALN
which is hydrolysed with water to obtain AL(OH)3.

(d) What is the major impurity present in iron when it is removed from the blast furnace?
Ans. Carbon.



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