GCSE%20Questions%20and%20Answers

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GCSE Questions and Answers Calculations

6 consecutive GCSE Chemistry papers 2002-7
2
I II II II II II II II II II III IV V VI VII VIII
1 H 1 ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom ? Atomic Number at the top ? Relative Atomic Mass at the bottom 2 He 4
3Li 7 4 Be 9 5 B 11 6 C 12 7 N 14 8 O 16 9 F 19 10 Ne 20
11 Na 23 12 Mg 24 13 Al 27 14 Si 28 15 P 21 16 S 32 17 Cl 35.5 18 Ar 40
19 K 39 20 Ca 40 21 Sc 45 22 Ti 48 23 V 51 24 Cr 52 25 Mn 55 26 Fe 56 27 Co 59 28 Ni 59 29 Cu 64 30 Zn 65 31 Ga 70 32 Ge 73 33 As 75 34 Se 79 35 Br 80 36 Kr 84
Relative Atomic Masses youll need.
Ammonium NH4 Hydroxide OH- Nitrate
NO3- Hydrogencarbonate HCO3- Hydrogen
sulphate HSO4- Carbonate CO32- Sulphate SO42-

2
3

• Covalent elements and Compounds

Covalent Elements Hydrogen H2 Chlorine
Cl2 Bromine Br2 Iodine
I2 Oxygen O2 Nitrogen N2 Helium
He Neon Ne Argon Ar
Covalent Compounds Water H2O Carbon
dioxide CO2 Carbon monoxide CO Sulphur
dioxide SO2 Sulphur trioxide
SO3 Ammonia NH3 Hydrogen peroxide
H2O2 Nitrogen monoxide NO Nitrogen dioxide
NO2
Sulphur S8 Phosphorus P4
4
To obtain full marks in this question, you must
show your working out5 When washing soda
crystals, Na2CO3.10H2O, are left exposed to the
atmosphere they lose water of crystallisation.
The longer they are left, the more water is
lost. The amount of water of crystallisation
remaining can be found in two ways either by
heating to remove all the remaining water or by
titration.
2002, Paper 1
5
5a) 2.675g of a sample of crystals were heated
to constant mass. The mass of the residue was
1.325g.(i) Why was the sample heated to
constant mass? ______________________________
1(ii) Calculate the number of moles of
anhydrous sodium carbonate in the
residue. ______________________________ 2
6
Consequential marking applies throughout5a) 2.67
5g of a sample of crystals were heated to
constant mass. The mass of the residue was
1.325g.(i) Why was the sample heated to
constant mass? To ensure that all water 1 (of
crystallisation) was lost. (ii) Calculat
e the number of moles of anhydrous sodium
carbonate in the residue. Na2CO3 1.325
0.0125 1 106 1
7
(iii) Calculate the mass of water lost and from
this calculate the number of moles of water
lost. _________________________________
______________________________ 3(iv) From
your answers to part (a)(ii) and (iii) above,
calculate the value of x in the formula
Na2CO3.xH2O. _________________________________
______________________________ 2
8
(iii) Calculate the mass of water lost and from
this calculate the number of moles of water
lost. Mass of water lost (2.765-1.325)
g 1.35g 1 Number of moles lost
1.35 0.075 1 18 1 (iv) From
your answers to part (a)(ii) and (iii) above,
calculate the value of x in the formula
Na2CO3.xH2O. Ratio of moles Na2CO3
H2O 0.0125 0.075 1
1 6 1
9
b) 1.775g of a different sample of washing soda
was dissolved in distilled water and made up of
a total volume of 250cm3. 25.0cm3 of this
solution were titrated with 0.08 mol/dm3 (moles
per litre) nitric acid. 31.25cm3 of acid were
required. The equation for the reaction
is Na2CO3 2HNO3 ? 2NaNO3 H2O
CO2(i) Calculate the number of moles of nitric
acid used in the titration. ____________________
__________________ ______________________________
_____ 2
10
b) 1.775g of a different sample of washing soda
was dissolved in distilled water and made up of
a total volume of 250cm3. 25.0cm3 of this
solution were titrated with 0.08 mol/dm3 (moles
per litre) nitric acid. 31.25cm3 of acid were
required. The equation for the reaction
is Na2CO3 2HNO3 ? 2NaNO3 H2O
CO2(i) Calculate the number of moles of nitric
acid used in the titration. Number of moles
HNO3 31.25 x 0.08 10001 2.5 x
10-3
11
(ii) Calculate the number of moles of sodium
carbonate present in the 25.0cm3
sample. _______________________________________
____________________________________2(iii) Cal
culate the number of moles of sodium carbonate
present in 250cm3 of solution. __________________
_____________________ ___________________________
_________2
12
Calculate the number of moles of sodium
carbonate present in the 25.0cm3 sample. Na2CO3
2HNO3 ? 2NaNO3 H2O CO2 mole ratio 1
2 1 Number of moles Na2CO3 2.5 x
10-3 2 1.25 x
10-3 (iii) Calculate the number of moles of
sodium carbonate present in 250cm3 of
solution. Number of moles Na2CO3 in 250cm3
1.25 x 10-3 x 10 1 1.25 x 10-2 1
13
Using your answer to part (b)(iii) and the mass
of sodium carbonate crystals weighed out find
the value of x in the formula Na2CO3.xH2O. ____
_____________________________ ___________________
___________2
14
Using your answer to part (b)(iii) and the mass
of sodium carbonate crystals weighed out find
the value of x in the formula Na2CO3.xH2O. Numb
er of moles moles rfmrfm mass
1.775 no. of moles 1.25 x 10-2 142
1rfm Na2CO3 106rfm x H2O 142 106 36
1x 36 2 1 18
15
c) Sodium hydrogencarbonate decomposes when it
is heated into sodium carbonate according to the
equation 2NaHCO3 ? NaCO3 H2O CO2 1.68g of
sodium hydrogencarbonate were placed in a test
tube and heated in a Bunsen flame for some
time.(i) Calculate the number of moles of
sodium hydrogencarbonate used. _________________
______________________ __________________________
__________ 2
16
c) Sodium hydrogencarbonate decomposes when it
is heated into sodium carbonate according to the
equation 2NaHCO3 ? NaCO3 H2O CO2 1.68g of
sodium hydrogencarbonate were placed in a test
tube and heated in a Bunsen flame for some
time.(i) Calculate the number of moles of
sodium hydrogencarbonate used. Number of moles
NaHCO3 1.68 84 1 0.02
1
17
(ii) Calculate the number of moles of sodium
carbonate formed. ______________________________
_____ ________________________________
2(iii) Calculate the mass of sodium
carbonate expected to be formed. ______________
_____________________ ___________________________
_____ 2
18
Calculate the number of moles of sodium
carbonate formed. Mole ratio NaHCO3
Na2CO3 2 1 1 number of moles Na2CO3
formed 0.02 0.01 1
2(iii) Calculate the mass of sodium carbonate
expected to be formed. Mass Na2CO3 expected
0.01 x 106 1 1.06g 1
19
(iv) Calculate the volume of carbon dioxide
produced in this experiment. (1 mole of gas
occupies 24dm3 at room temperature and
pressure) _____________________________________
__________________________________ 2
20
(iv) Calculate the volume of carbon dioxide
produced in this experiment. (1 mole of gas
occupies 24dm3 at room temperature and
pressure) Mole ratio NaHCO3 CO2 2
1 1 Number of moles CO2 expected
0.02 0.01 1 Volume of CO2 expected 24 x
0.01 0.24dm3 1 or 240cm3
21
4 To obtain full marks in this question, all
steps in the calculation must be
shown.a) Copper carbonate, CuCO3 decomposes on
heating according to the following
equation CuCO3 ? CuO CO2 (Relative atomic
masses C 12 O 16 Cu 64) The following
results were obtained in an experiment in which
a sample of copper carbonate was to be heated.
Mass of empty crucible 24.21g Mass of
crucible and sample of copper carbonate 27.31g
2003, Paper 1
22
(i) What colour change would you observe on
heating the sample of copper carbonate? ________
_______________________ 2(ii) Calculate the
mass of copper carbonate in the
crucible. _______________________________ 1
23
(i) What colour change would you observe on
heating the sample of copper carbonate? Green
1 to black 1 2(ii) Calculate the
mass of copper carbonate in the crucible. 27.31
24.21 3.1g 1
24
(iii) Calculate the mass of solid copper oxide,
CuO, which you would expect to obtain from the
complete decomposition of this sample of copper
carbonate.
25
(iii) Calculate the mass of solid copper oxide,
CuO, which you would expect to obtain from the
complete decomposition of this sample of copper
carbonate. 0.025 1 moles of
CuCO3 CuCO3 CuO 11 1 0.025 1
moles of CuO 0.025 x 80 1 2.0 1g
26
(iv) How would you ensure all the copper
carbonate had decomposed? ______________________
_________ 1
27
(iv) How would you ensure all the copper
carbonate had decomposed? Heat to constant
mass 1
28
b) The experiment was carried out, heating the
sample for 3 minutes. Not all of the copper
carbonate had decomposed in this time. The
results obtained are shown below
Mass of empty crucible 24.21g
Mass of crucible and sample of copper carbonate 27.31g
Mass of crucible and solid after heating for 3 minutes 26.43g
29
(i) What mass of solid remained after heating
for 3 minutes? _______________________________
2(ii) Calculate the mass of carbon dioxide
gas lost in this experiment. ___________________
____________ 2
30
(i) What mass of solid remained after heating
for 3 minutes? 26.43 24.21 1 2.22
1g (ii) Calculate the mass of carbon
dioxide gas lost in this experiment. 27.31
26.43 1 0.88 1 g
31
(iii) Calculate the number of moles of carbon
dioxide gas lost in this experiment. ___________
____________________ 2(iv) Calculate the mass
of copper carbonate which must have been
decomposed in this experiment. _________________
_________________ _______________________________

32
(iii) Calculate the number of moles of carbon
dioxide gas lost in this experiment. 0.02
1 moles of CO2 (iv) Calculate the mass of
copper carbonate which must have been decomposed
in this experiment. CO2 CuCO3 1
1 0.02 1 moles of CuCO3 decomposed 0.02
x 124 2.48 1g of CuCO3 decomposed
33
v) Using your answer to parts (a)(ii) and
(b)(iv), calculate the percentage of copper
carbonate in the original sample which must
have been decomposed in this experiment.
2
34
v) Using your answer to parts (a)(ii) and
(b)(iv), calculate the percentage of copper
carbonate in the original sample which must
have been decomposed in this experiment. x
100 1 80 2
35
c) Copper carbonate reacts with sulphuric acid
and crystals of hydrated copper sulphate,
CuSO4.5H2O, can be obtained. Calculate the
percentage of water of crystallisation in
hydrated copper sulphate, CuSO4.5H2O. (Relative
atomic masses H1 O16 Cu64)
3
36
c) Copper carbonate reacts with sulphuric acid
and crystals of hydrated copper sulphate,
CuSO4.5H2O, can be obtained. Calculate the
percentage of water of crystallisation in
hydrated copper sulphate, CuSO4.5H2O. (Relative
atomic masses H1 O16 Cu64) 3 CuSO4.5H2O
RFM 250 1 Mass of water 18 x 5 90
1 Percentage water x 100 36 1
37
d) Carbon dioxide reacts with excess sodium
hydroxide solution according to the following
equation CO2 2NaOH ? Na2CO3 H2O (1 mole
of any gas at room temperature and pressure
occupies 24 000cm3) 120cm3 of carbon dioxide
gas is passed into 150cm3 of 0.1mol/dm3 moles
per litre.mol/l sodium hydroxide solution.
38
(i) Calculate the number of moles in 120cm3 of
carbon dioxide gas. ____________________________
_________ __________________________________ 2
39
(i) Calculate the number of moles in 120cm3 of
carbon dioxide gas. 1 0.005 1 moles
CO2
40
(ii) Calculate the number of moles of sodium
hydroxide needed to react with this amount of
carbon dioxide. ________________________________
_____ __________________________________ 2
41
(ii) Calculate the number of moles of sodium
hydroxide needed to react with this amount of
carbon dioxide. CO2 NaOH 1 0.005 moles
x 2 0.01 moles NaOH needed 1
42
(iii) Calculate the number of moles in 150cm3 of
0.1mol/dm3 sodium hydroxide solution. __________
___________________________ _____________________
_____________ 2
43
(iii) Calculate the number of moles in 150cm3 of
0.1mol/dm3 sodium hydroxide solution. 1
0.015 1 moles NaOH 2
44
(iv) How many moles of sodium hydroxide are left
at the end of the reaction? ____________________
_________________ _______________________________
___ 2
45
(iv) How many moles of sodium hydroxide are left
at the end of the reaction? Moles NaOH needed to
react with CO2 2 x 0.005 0.01 Moles
NaOH remaining 0.015 0.01 1 0.005
1
46
e) Sodium hydroxide can be neutralised by
hydrochloric acid according to the
equation. NaOH HCl ? NaCl H2O Using your
answer to part (d)(iv) calculate the number of
0.5 mol/dm3 hydrochloric acid which would be
required to neutralise the sodium hydroxide left
at the end of the reaction. ____________________
_________________ _______________________________
___ 4
47
e) Sodium hydroxide can be neutralised by
hydrochloric acid according to the
equation. NaOH HCl ? NaCl H2O Using your
answer to part (d)(iv) calculate the number of
0.5 mol/dm3 hydrochloric acid which would be
required to neutralise the sodium hydroxide left
at the end of the reaction. NaOH HCl 1.1
1 moles HCl required 0.005
1 volume HCl required 1
10 1 cm3
48
5 To obtain full marks in this question, all
steps in the calculation must be shown.a) In
1908 a German chemist called Fritz Haber
succeeded in combining nitrogen with hydrogen
to form ammonia. N2 3H2 ? 2NH3
2004, Paper 1
49
Calculate the volume of nitrogen gas, measured
at room temperature and pressure, needed to
produce 10dm3 of ammonia.
50
Calculate the volume of nitrogen gas, measured
at room temperature and pressure, needed to
produce 10dm3 of ammonia. 1 volume of nitrogen
needs 2 volumes of ammonia 1 hence 10dm3
needs 5dm3/4.99 1 dm3
51
b) A concentrated solution of ammonia can be used
as a fertiliser. To determine the concentration
of the ammonia it was first diluted by measuring
10.0cm3 and making the volume up to 1dm3
(1000cm3). A 25.0cm3 sample of this dilute
ammonia solution was then titrated against 0.05
mol/dm3 (moles per litre) sulphuric acid. The
25.0 cm3 of diluted ammonia required 12.5cm3 of
the acid for neutralisation. The equation for
the titration is 2NH3 H2SO4 ? (NH4)2SO4
52
(i) Calculate the number of moles of sulphuric
acid used in the titration.(ii) Calculate the
number of moles of ammonia in the 25.0cm3 sample
which reacted with the acid.
53
(i) Calculate the number of moles of sulphuric
acid used in the titration. Number of moles of
sulphuric acid 0.000625 2
(ii) Calculate the number of moles of ammonia
in the 25.0cm3 sample which reacted with the
acid. From equation (12) 1 mole sulphuric
acid reacts with 2 moles of ammonia
1 0.000625 moles acid reacts with 0.00125
moles ammonia 1
54
(iii) Calculate the concentration of the dilute
ammonia solution in mol/dm3 (moles per
litre).(iv) Calculate the concentration of the
original concentrated ammonia solution in
mol/dm3 (moles per litre).
55
(iii) Calculate the concentration of the dilute
ammonia solution in mol/dm3 (moles per
litre). Concentration of ammonia
0.05 1 mol/dm3(iv) Calculate the
concentration of the original concentrated
ammonia solution in mol/dm3 (moles per
litre). Diluted 100 times 1 original conc
0.05 x 100 5 1 mol/dm3
56
(v) Calculate the concentration of the original
concentrated ammonia solution in g/dm3
57
(v) Calculate the concentration of the original
concentrated ammonia solution in g/dm3 RFM of
NH3 171 conc g/dm3 5 x 171 851
g/dm3
58
c) Solid fertilisers are easier to store, hence
fertilisers like solid ammonium chloride are
preferred over ammonia solution. To produce
ammonium chloride, ammonia is reacted with
hydrochloric acid, according to the equation
below. NH3 HCl ? NH4Cl
59
What mass of ammonium chloride is formed when 73g
of hydrochloric acid are completely neutralised
by ammonia?(Relative atomic masses H1, N14,
Cl35.5
60
What mass of ammonium chloride is formed when 73g
of hydrochloric acid are completely neutralised
by ammonia?(Relative atomic masses H1, N14,
Cl35.5RFM of HCl 36.5 1moles of HCl
73/36.5 21(ratio 11 hence) moles NH4Cl
21RFM of NH4Cl 53.512 x 53.5 107g1
61
d) Another important fertiliser made from
ammonia is urea. It contains 20.00 carbon,
6.66 hydrogen, 46.67 nitrogen and 26.67
oxygen. Calculate the formula of
urea. (Relative atomic masses H1, C12,
N14, O16)
62
d) Another important fertiliser made from
ammonia is urea. It contains 20.00 carbon,
6.66 hydrogen, 46.67 nitrogen and 26.67
oxygen. Calculate the formula of
urea. (Relative atomic masses H1, C12, N14,
O16) In 100g of compound there are 20/12
moles C 1.67 1 6.67/1 moles H 6.67
1 46.67/14 moles N 3.331 26.67/16 moles O
1.671 formula is CH4N2O 1 accept any
correct whole number multiple.
63
e) Car exhaust fumes contain harmful nitrogen
monoxide gas. Research has shown that when a
stream of ammonia gas is injected into the hot
exhaust a reaction occurs which converts the
harmful nitrogen monoxide, NO, to nitrogen gas
according to the equation below. 6NO 4NH3 ?
5N2 6H2O
64
(i) How many moles of ammonia would be needed to
react with 0.6 moles of nitrogen monoxide,
NO? ___________________________ 1
65
(i) How many moles of ammonia would be needed to
react with 0.6 moles of nitrogen monoxide,
NO? 0.4 moles 1
66
(ii) The average car emits 0.033 moles of
nitrogen monoxide per km. How many moles of
ammonia would be needed to convert this to N2
gas? ___________________________ 2
67
(ii) The average car emits 0.033 moles of
nitrogen monoxide per km. How many moles of
ammonia would be needed to convert this to N2
gas? 6 moles NO 4 moles NH3/0.033moles
NO 0.033/6x4 1 0.022 1 moles per km
68
(iii) Using your answer to (e)(ii) calculate the
mass of ammonia needed to convert 0.033 moles of
NO to N2 gas. ___________________________ 2
69
(iii) Using your answer to (e)(ii) calculate the
mass of ammonia needed to convert 0.033 moles of
NO to N2 gas. 0.022 x 171 0.374g 1
70
2 Lead is extracted from the ore galena,
PbS.a) The ore is roasted in air to produce
lead(II) oxide, PbO. 2PbS(s) 3O2(g) ?
2PbO(s) 2SO2(g) (Relative Atomic Masses
Pb207, S32, O16)(i) Calculate the mass of
lead(II) oxide, PbO, produced from 2390g of
galena, PbS. (Show all steps in your
calculations. 5
2005, Paper 2
71
(i) Calculate the mass of lead(II) oxide, PbO,
produced from 2390g of galena, PbS. (Show all
steps in your calculations. 5 RFM PbS
20732 239 1 Moles PbS 10 1 Moles
PbS 10 1 RFM PbO 27016 223 1 Mass
PbO 10x223 2230g or 2.23kg 1
72
The lead(II) oxide is reduced to lead by heating
it with carbon in a blast furnace.PbO(s) C(s)
? Pb(l) CO(g)The molten lead is tapped off
from the bottom of the furnace.(ii) Using your
answer to part (a)(i), calculate the mass of
lead that would eventually be produced.
73
(ii) Using your answer to part (a)(i), calculate
the mass of lead that would eventually be
produced. PbO Pb 11 1 Moles Pb 10
1 Mass Pb 10 x 270 2070g or 2.07kg 1
74
b) Lead metal forms several oxides. The formula
of lead oxide may be represented as PbxOy. In
an experiment to find the formula of a sample of
lead oxide, a porcelain dish was weighed and the
mass recorded. The porcelain dish was then
filled with the lead oxide and reweighed. The
mass was again recorded.
75
The dish was placed in a hard-glass tube and
heated in a stream of hydrogen gas. The hydrogen
reduced all of the lead oxide to a bead of
silvery lead metal. The apparatus was allowed to
cool and the dish and its contents were
reweighed.
76
(i) Calculate the mass of lead metal
produced. _____________________________________
1(ii) Calculate the mass of oxygen present in
the lead oxide. ________________________________
_____ 1
77
(i) Calculate the mass of lead metal
produced. 27.56 21.35 6.21g
1(ii) Calculate the mass of oxygen present in
the lead oxide. 28.20 27.56 0.64g
1
78
(iii) Using your answers to (i) and (ii),
calculate the formula of the sample of lead
oxide. (Relative atomic masses Pb207, O16)
79
(iii) Using your answers to (i) and (ii),
calculate the formula of the sample of lead
oxide. (Relative atomic masses Pb207,
O16) Moles Pb 0.03 1 Moles O
0.04 1 Ratio 34 so formula is Pb3O4 1
80
c) Titration is a technique used by chemists to
find the concentration of a solution. The
apparatus used in a titration is shown
opposite.
81
(i) Identify the pieces of apparatus A and B. A
is a ________________________________ 1 B is a
________________________________
1(ii) Describe in detail, stating precautions
to ensure safety and accuracy, how you would
transfer 25.0cm3 of an alkali into the conical
flask using the piece of apparatus
A. _____________________________________ _______
______________________________ __________________
___________________ _____________________________
________ 3
82
(i) Identify the pieces of apparatus A and B. A
is a pipette 1 B is a burette
1(ii) Describe in detail, stating
precautions to ensure safety and accuracy, how
you would transfer 25.0cm3 of an alkali into the
conical flask using the piece of apparatus
A. Rinse with deionised water 1 rinse with
alkali 1 use safety pipette filler/safety
goggles 1 to draw up liquid until bottom of
meniscus on line 1 release 1 into conical
flask touch tip of pipette to surface of alkai
1 (Max 3)
83
(iii) Describe in detail, stating precautions to
ensure accuracy, the steps you would take to
prepare the piece of apparatus B for use in a
titration. _______________________________ _____
__________________________ ______________________
_________ _______________________________ 4
84
(iii) Describe in detail, stating precautions to
ensure accuracy, the steps you would take to
prepare the piece of apparatus B for use in a
titration. Rinse with deionised water 1 rinse
with solution 1 fill burette with solution
1 use funnel 1 ensure jet is filled 1
ensure no air bubbles 1 (Max 4)
85
d) Limewater is calcium hydroxide solution. In a
titration to find the concentration of calcium
hydroxide in limewater, 25.0cm3 of limewater
required 16.4cm3 of hydrochloric acid of
concentration 0.040 mol/dm3 for
neutralisation. (Relative atomic masses Ca40,
O16, H1) Ca(OH)2 2HCl ? CaCl2 2H2O
86
(i) Calculate the concentration of the calcium
hydroxide in mol/dm3 (mol per litre). Answer
__________________ mol/dm3 4(ii) Calculate
the concentration of the calcium hydroxide in
g/dm3 (grams per litre). Answer
__________________ mol/dm3 4
87
(i) Calculate the concentration of the calcium
hydroxide in mol/dm3 (mol per litre). Answer
0.000656 1 Moles Ca(OH)2
0.000328 1 x 1000 1 0.01312
mol/dm3 (ii) Calculate the concentration of the
calcium hydroxide in g/dm3 (grams per
litre). Answer Mass mol x RFM
0.01312 x 74 1 0.971
1 g/dm3
88
7a) Oxygen forms ozone gas, O3, in the upper
atmosphere according to the equation 3O2(g) ?
2O3(g) 150m3 of oxygen reacts completely to
form ozone.
2006, Paper 2
89
(i) State Avogadros Law _______________________
________ _______________________________ _______
________________________ 3
90
(i) State Avogadros Law Equal volumes of gas
1 under the same conditions of temperature and
pressure 1 contain the same number of
particles 1 or moles of ozone 4.2 moles
3
91
(ii) Using Avogadros Law or otherwise,
calculate the volume of ozone gas
produced. ____________________________m3
2
92
(ii) Using Avogadros Law or otherwise,
calculate the volume of ozone gas
produced. 2
93
b) In the laboratory ozone gas can be produced by
passing an electrical discharge through dry air.
450cm3 of ozone gas is produced when the
temperature is 300K and the pressure is 1
atmosphere. The ozone gas is compressed using
a pressure of 8 atmospheres and the temperature
is decreased to 200K. Calculate the volume of
ozone gas under these new conditions. _________
______________________cm3 4
94
b) Calculate the volume of ozone gas under these
new conditions. ______________________
_________ 4
95
c) Ozone is used in very small amounts in
underground railway stations to remove
compounds which cause stations to be stuffy.
One of the compounds which is formed is
formaldehyde CH2O. Calculate the percentage by
mass of carbon in CH2O. _______________________
_____ 3
96
c) Calculate the percentage by mass of carbon in
CH2O. RFM (CH2O) 30 1 carbon
1 40 1 3
97
d) 1.92g of sulphur dioxide SO2, reacts
completely with ozone to form 2.40g of sulphur
trioxide, SO3.(i) Calculate the number of moles
of sulphur dioxide used. _______________________
________ 2
98
d) 1.92g of sulphur dioxide SO2, reacts
completely with ozone to form 2.40g of sulphur
trioxide, SO3.(i) Calculate the number of moles
of sulphur dioxide used. RFM (SO2) 64
1 Moles 0.03 1 2
99
(ii) Calculate the mass of ozone which
reacts. _______________________________
1(iii) Calculate the number of moles of ozone
which reacts. _______________________________
2
100
(ii) Calculate the mass of ozone which
reacts. 2.4 1.92 0.48g
1(iii) Calculate the number of moles of ozone
which reacts. RFM (O3) 481 Moles
0.01 1 2
101
(iv) Calculate the number of moles of sulphur
trioxide formed. _______________________________
2
102
(iv) Calculate the number of moles of sulphur
trioxide formed. RFM (SO3) 801
Moles 0.031 2
103
(v) Using your answers to (i), (iii) and (iv) or
otherwise, balance the symbol equation for the
reaction. Equation SO2 O3 ? SO3 1
104
(v) Using your answers to (i), (iii) and (iv) or
otherwise, balance the symbol equation for the
reaction. Equation SO2 O3 ? SO3
1 Ratio SO2 O3 SO3 0.03 0.01 0.03
3 1 3Equation 3SO O3 ? 3SO2 balancing
numbers 1
105
e) Oxygen gas is prepared by the decomposition
of hydrogen peroxide solution using the catalyst
manganese(IV) oxygen. 2H2O2 ? 2H2O O2 A
solution of hydrogen peroxide is labelled
0.1mol/dm3 (moles per litre). 25.0cm3 of this
solution is decomposed completely using
manganese(IV) oxide.
106
(i) What is meant by the term catalyst? ________
_______________________ _________________________
______ 3
107
(i) What is meant by the term catalyst? Substanc
e which speeds up/increases the rate of 1 a
(chemical) reaction 1 without being used
up/chemically unchanged at the end 1
3
108
(ii) Calculate the volume of oxygen gas produced
in this decomposition. State the units. (1
mole of any gas occupies a volume of
24dm3) __________________________________ 7
109
(ii) Calculate the volume of oxygen gas produced
in this decomposition. State the units. (1
mole of any gas occupies a volume of
24dm3) Moles of H2O2 Ratio H2O2
O2 2 1 1 Moles of O2
Volume of oxygen 0.00125 x 24 1 0.03
1dm3 1 (or volume of oxygen 0.00125 x
24000 1 301cm31
110
5 Borax is a salt which is hydrated and is used
in cleaning agents. The formula may be
represented by Na2B4O7.xH2O. Borax dissolves in
water to give a solution which acts as a weak
alkali.
2007, Paper 1
111
a) 4.775g of Borax were weighed out and made up
to a volume of 250cm3 with deionised water.
25.0cm3 portions of this solution were titrated
against nitric acid of concentration 0.094
mol/dm3 (moles per litre). The results were
recorded in the table below.
Initial burette reading (cm3) Final burette reading (cm3) Volume of nitric acid used (titre) (cm3)
Rough Titration 0.0 26.9 26.9
1st Accurate Titration 0.0 26.7 26.7
2nd Accurate Titration 0.0 26.5 26.5
112
(i) Calculate the average
titre. _______________________________ 2
Initial burette reading (cm3) Final burette reading (cm3) Volume of nitric acid used (titre) (cm3)
Rough Titration 0.0 26.9 26.9
1st Accurate Titration 0.0 26.7 26.7
2nd Accurate Titration 0.0 26.5 26.5
113
(i) Calculate the average titre. 26.2 2. If
rough used average 26.7 award 1 2
114
(ii) The indicator used was methyl orange.
State the colour change of the indicator in
this titration. From ____________ to
____________ 2
115
(ii) The indicator used was methyl orange.
State the colour change of the indicator in
this titration. From orange or yellow 1 to
pink or red 1 (wrong way round) 1 2
116
(iii) Calculate the number of moles of nitric
acid used in this titrations. _________________
______________ 2
117
(iii) Calculate the number of moles of nitric
acid used in this titrations. Moles 1
0.0025 1 (2.5 x 10-3)
118
The equation for the reaction isNa2B4O7 2HNO3
5H2O ? 2NaNO3 4H3BO3(iv) Use the equation
to deduce the number of moles of Borax which
reacted with the nitric acid. __________________
________________ ________________________________
_____ 2
119
The equation for the reaction isNa2B4O7 2HNO3
5H2O ? 2NaNO3 4H3BO3(iv) Use the equation
to deduce the number of moles of Borax which
reacted with the nitric acid. 1 mole borax 2
moles nitric acid or 0.00125 1 (1.25 x
10-3) 2
120
(v) Calculate the concentration of the Borax in
mol/dm3 (moles per litre) _____________________
__________ _______________________________ 2
121
(v) Calculate the concentration of the Borax in
mol/dm3 (moles per litre) conc 1
0.05 1 mol/dm3 2
122
(vi) From the mass of Borax used, calculate the
concentration of Borax in g/dm3 _______________
________________ 1
123
(vi) From the mass of Borax used, calculate the
concentration of Borax in g/dm3 4.775g in
250cm3 ? 4.775 x 4 19.1 1 g/dm3 1
124
(vii) Using your answers to parts (v) and (vi)
find the formula mass of the Borax,
Na2B4O7.xH2O, and hence find the value of x.
(Relative atomic masses H 1 B 11 O 16
Na 23) _______________________________
_______________________________
_______________________________ 3
125
(vii) Using your answers to parts (v) and (vi)
find the formula mass of the Borax,
Na2B4O7.xH2O, and hence find the value of x.
(Relative atomic masses H 1 B 11 O 16
Na 23) 382 1 382 202 1
18x 18x 180 x 10 1 3
126
b) When Borax crystals are left in air they lose
some of their water of crystallisation. To find
the value of x in a sample of hydrated Borax
Na2B4O7.xH2O, which had been left in air for a
month, the sample was heated to constant mass.
7.28g of hydrated Borax produced 4.04g of
anhydrous Borax. (Relative atomic masses H
1 B 11 O 16 Na 23)
127
(i) What is meant by heated to constant
mass? _______________________________
2(ii) Calculate the mass of water
lost. _______________________________ 1
128
(i) What is meant by heated to constant
mass? heating and weighing 1 repeat until 2
readings the same 1 2(ii) Calculate the
mass of water lost. 3.25g, 7.28 4.04
3.24g 1
129
(iii) Calculate the number of moles of water
lost. _______________________________ _________
______________________ 2(iv) Calculate the
number of moles of anhydrous Borax. ____________
___________________ 1
130
(iii) Calculate the number of moles of water
lost. moles 1 0.18 1
2(iv) Calculate the number of moles of
anhydrous Borax. Moles 0.02 1
131
(v) Using your answers to (iii) and (iv)
determine the value of x in Na2B4O7.xH2O. ____
___________________________ _____________________
__________ 2
132
(v) Using your answers to (iii) and (iv)
determine the value of x in Na2B4O7.xH2O. bora
x water 0.02 0.18 1 1 9 x
91 2
133
c) When anhydrous Borax is heated it decomposes
according to the equation
Anhydrous Borax ? Sodium metaborate Boric Oxide
Na2B4O7 ? 2NaBO2 B2O3
134
Calculate the mass of sodium metaborate which
is produced when 5.05g of anhydrous Borax is
heated. (Relative atomic masses B 11 O 16
Na 23)
135
Calculate the mass of sodium metaborate which
is produced when 5.05g of anhydrous Borax is
heated. (Relative atomic masses B 11 O 16
Na 23) Moles of anhydrous borax 0.025
1 Ratio 1 borax 2 sodium metaborate 0.025
0.0501 0.05x661 3.3 1g
136
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