Candidate
Centre Number
Number
Candidate Name
International General Certificate of Secondary Education
UNIVERSITYOF CAMBRIDGELOCALEXAMINATIONS
SYNDICATE
CHEMISTRY
PAPER 3
Tuesday
15 NOVEMBER 1994
0620/3
Afternoon
1 hour 15 minutes
Candidates answer on the question paper.
Additional materials:
Mathematical tables
(
TIME
'-../
1 hour 15 minutes
INSTRUCTIONS TO CANDIDATES
Write your name, Centre number and candidate number in the spaces at the top of this page.
Answer all questions.
Write your answers in the spaces provided on the question paper.
INFORMATION FOR CANDIDATES
The number of marks is given in brackets [ ] at the end of each question or part question.
Mathematical tables are available.
You may use your calculator.
A copy of the Periodic Table is printed on page 12.
(
'--'
FOR EXAMINER'S USE
1
2
3
4
5
TOTAL
This question paper consists of 12 printed pages.
sa (ST) OK42308
~ UCLES 1994
[Turn over
1
An extract from a magazine highlights how much energy can be saved by recycling:
ENERGY SAVED BY RECYCLING
0
BOTTLE BANK
GREEN GLASS ONLY
ENVIRONMENTAL SERVICES
'-/
material
v
energy saved by
recycling
energy needed for original
production, in GJ/tonne
percentage %
250
100
30
16
aluminium
plastics
paper
glass
95
88
35
5
1 GJ = 1000 million joules
To produce one. tonne of paper from wood pulp requires 30 GJ of energy. To make one tonne
of paper recycling saves 30 x 35/100 = 10.5 GJ.
(a) Very large savings of energy can be made by recycling aluminium.
(i)
How much energy is needed to produce one tonne of aluminium by recycling?
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[2]
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(Ii)
Describe how aluminium is extracted from pure aluminium oxide.
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[4]
Use the answer to (a) (II) to explain why recycling saves so much energy.
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(iv)
Most metals need some surface coating (for example, paint) to prevent corrosion.
Explain why aluminium does not need this protection.
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[1]
(b) Glass is made from sodium carbonate, calcium carbonate and sand. Energy is supplied
and the chemicals react to form a mixture of metal silicates. This is glass.
(I)
What type of reaction takes place when glass is made?
[1]
"
(II)
Complete the equation:
CaCO3 + SiO2
CaSiO3 +
[1]
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(c) Sand is silicon(IV) oxide (silicon dioxide). It has a macromolecular structure. Carbon
dioxide has a molecular structure.
(i)
Name a substance that has a similar structure to that of silicon(IV) oxide.
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(ii)
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[1]
Give a difference in physical properties between silicon(IV) oxide and carbon
dioxide.
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(iil)
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[1] .
Show the arrangement of valency electrons in a molecule of carbon dioxide by
completing the diagram.
Use x to represent an electron from carbon.
Use 0 to represent an electron from oxygen.
0
c 0
[2]
(Iv)
In the structure of silicon(IV) oxide:
how many oxygen atoms are there around each silicon atom; ....................................
how many silicon atoms are there around each oxygen atom?
062013W94
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[2]
[Turn over
2
The diagram shows the nutritional information on a packet of dried apricots.
DRIED APRICOTS
NUTRITIONALi NFORMATION
I
in 100 9 of product
---------
Protein
Carbohydrates
40 g
Sugar
40 g
Fibre
15 g
732 kJ
Energy
Preservative E 220
Produce of Turkey
(a) (I)
Which one of the three main constituents of food is not listed?
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(ii)
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How much protein is there in 100g of the dried apricots?
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(b) Preservative E220 is sulphur dioxide.
(I)
How does it preserve food?
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(II)
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Sulphur dioxide can be made by burning sulphur in air.
Name a source of sulphur.
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(Iii)
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Why is sulphur dioxide used in the manufacture of wood pulp?
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(c) As part of her project, a pupil was studying dried apricots. She found out that sulphur
dioxide would react with water to form sulphurous acid.
S02 + H2O-+- H2S03
She left the dried apricots in water for several hours to extract the sulphur dioxide. The
resulting solution of sulphurous acid was used for the following tests.
(I)
Sulphurous acid is a reducing agent.
What would be observed on adding a few drops of aqueous potassium manganate(VII)
to sulphurous acid?
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(Ii)
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[2]
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She added hydrogen peroxide to the sulphurous acid and then tested for a sulphate.
The test was positive.
Describe the test for a sulphate.
Reagent
Result..
(iii)
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[2]
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The hydrogen peroxide oxidised sulphurous acid, a weak acid, to sulphuric acid, a
strong acid.
Explain each of the following:
acid
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weak acid
strong
acid
[2]
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[1]
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[1]
(d) The second part of the project was to identify some of the sugars present in the apricots.
The apricots were ground with a mixture of water and ethanol. The sugars dissolved in
this solvent.
Describe how you could separate and identify the sugars. which are colourless.
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[2]
0
3
(a) An all-metal Viking sword was discovered.
metal hilt
iron blade
The hilt was not corroded. The iron blade was badly rusted, especially near the hilt.
(I)
Name a metallic element that does not corrode.
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(II)
Suggest a reason why the rusting was greatest near the hilt.
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(iii)
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[1]
[1]
A modern sword blade would be made out of an alloy of iron that does not corrode.
What is the name of this alloy and what two other elements are in it?
Name of alloy
Names of other elements
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[1]
[2]
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(b) Metals are malleable and can be beaten into the shape of a sword. Why are metals
malleable?
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...................................................
[2]
(c) To find out if iron was more reactive than tin the following experiment was carried out:
The surface of a piece of iron was cleaned. The iron was added to aqueous tin(lI)
chloride and left for a few minutes. If iron is more reactive than tin, there would be
deposits of tin on the surface of the iron.
This experiment could be repeated with different metals. The results of these experiments
are given in the table below.
iron
aqueous solution
tin
scandium
mercury
x
iron(ll) chloride
tin(ll) chloride
X
./
scandium chloride
mercury(ll) chloride
./
......
= reaction occurred
)( = no reaction
[1]
(i)
Complete the table.
(ii)
What is the order of reactivity of the four metals?
1 (Most reactive)
2
,
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.....
,...,..............................
3
[2]
4 (Least reactive) ..........................................
(iil)
Write a symbol equation for the reaction between scandium atoms and tin(ll) ions, A
scandium ion has a charge of 3+,
.
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[2]
4
--
Hydrogen and bromine react to form hydrogen bromide. .
--
H2+ Br2-+- 2HBr
(a) When a reaction takes place, chemical bonds are broken and new chemical bonds are
formed.
To break a chemical bond, energy has to be supplied; this is represented by +.
-~
When a chemical bond forms, energy is given out; this is represented by
(I)
Insert the missing signs and the missing value in the table below.
Energy to break H-H =
Energy to break Br-Br =
Energy to make H-Br
Energy to make H-Br
(II)
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[1]
Is the overall reaction exothermic or endothermic?
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=
=
+ 436kJ
...190kJ
...366kJ
kJ
Calculate the overall energy change for this reaction.
.
(III)
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[1]
(b) Bromine reacts with alkanes in a similar way to chlorine. Hydrogen bromide is made in
the substitution reaction between propane and bromine.
PROPANE + BROMINE-+(i)
BROMOPROPANE + HYDROGEN BROMIDE
Draw the structure of propane.
[1]
(ii)
Draw the structure of a bromopropane.
[1]
(iii)
The reaction between propane and bromine is photochemical.
Suggest what is meant by photochemical.
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[2].
(c) A preparation of the insoluble compound lead(lI) bromide is described below.
To 10 cm3 of aqueous lead(lI) nitrate, 20 cm3 of aqueous potassium bromide was added.
The concentration of each of these solutions was 1.00 molldm3. The mixture was filtered
and the precipitate was washed with water. Finally, the solid was dried in an oven.
(i)
Complete the ionic equation.
Pb2+
+
Br-~
........................
[2]
(i~) Explain why the volume of aqueous potassium bromide used was double that of the
aqueous lead(lI) nitrate.
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(iii)
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[1]
Why was it necessary to 'filter and wash'?
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062013W94
[2]
[Turn over
IV
(d) In the experiment, 0.010 mol of lead(lI) nitrate was used and 2.21 g of lead(lI) bromide
were produced.
Calculate the percentage yield of lead(lI) bromide.
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5
[3]
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The table shows some of the elements needed by green plants.
taken up
by plant as
element
./
(a) (I)
nitrogen
NO3- or NH4+
to make amino acids
and proteins
magnesium
Mg2+
part of chlorophyll
molecule
sulphur.
SOi-
to make protein
containing sulphur
potassium
K+
making enzymes
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Why is chlorophyll essential for the growth of green plants?
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What element. essential for plant growth, is not mentioned in the table?
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(II)
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What are enzymes?
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(b) When plant material is burnt, an alkaline ash is formed. In Africa, a useful product was
made by heating a mixture of plant ash, animal fat and water.
(i)
What type of reaction occurs between the alkali from the ash and the ester linkage in
the fat?
.
(II)
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[1]
From your answer to (I), give the common name of the product.
.
[1]
(c) A shortage of the sulphate ion in plants causes chlorosis, a yellowing of the leaves. In
industrial countries,this yellowingis not observeddue to atmosphericpollution.
Suggest an explanation.
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[3]
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(d) Nitrogen is needed for the synthesis of amino acids and vegetable proteins.
(I)
How can vegetable protein be broken down in to its constituent amino acids?
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(II)
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What is the name of the linkage common to both proteins and nylon?
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(Iii)
............................................................
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[1]'
What difference in structure is there between protein and nylon?
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