CandidateCentre Number Number

Candidate Name

International General Certificate of Secondary EducationUNIVERSITYOF CAMBRIDGELOCALEXAMINATIONSSYNDICATE

CHEMISTRYPAPER 3

0620/3

Tuesday 15 NOVEMBER 1994 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.(

'--'

This question paper consists of 12 printed pages.sa (ST) OK42308~ UCLES 1994 [Turn over

FOR EXAMINER'S USE

1

2

3

4

5

TOTAL

1 An extract from a magazine highlights how much energy can be saved by recycling:

ENERGY SAVED BY RECYCLING

0BOTTLE BANK

GREEN GLASS ONLY

ENVIRONMENTAL SERVICES v

'-/ material energy needed for originalproduction, in GJ/tonne

aluminiumplasticspaperglass

1 GJ = 1000 million joules

To produce one. tonne of paper from wood pulp requires 30 GJ of energy. To make one tonneof paper recycling saves 30 x 35/100 = 10.5 GJ.

2501003016

energy saved byrecycling

percentage %

958835

5

(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?

., """""'" .." [2]"---'

(Ii) Describe how aluminium is extracted from pure aluminium oxide.

.. " .,.. ... ........

.. ".. """'" , ,. ............

, """"""""""'" ".. ....

"""""""" ,.. ..., """"

" ~ [4]

(III) Use the answer to (a) (II) to explain why recycling saves so much energy.

'" " , ..., [1]

(iv) Most metals need some surface coating (for example, paint) to prevent corrosion.

Explain why aluminium does not need this protection.

".. """"'" [1]

(b) Glass is made from sodium carbonate, calcium carbonate and sand. Energy is suppliedand 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]

(c) Sand is silicon(IV) oxide (silicon dioxide). It has a macromolecular structure. Carbondioxide has a molecular structure.

(i) Name a substance that has a similar structure to that of silicon(IV) oxide.

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(ii) Give a difference in physical properties between silicon(IV) oxide and carbondioxide.

"""""""""""'" " [1] .

(iil) Show the arrangement of valency electrons in a molecule of carbon dioxide bycompleting 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? """,""""""""""'" [2]

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2 The diagram shows the nutritional information on a packet of dried apricots.

DRIED APRICOTS

I NUTRITIONALi NFORMATION

in 100 9 of product

Protein ---------

Carbohydrates 40 g

Sugar 40 g

Fibre 15 g

Energy

Preservative E 220

732 kJ

Produce of Turkey

(a) (I) Which one of the three main constituents of food is not listed?

" ". ..oo. oo... """'oo.. """""oo' oo., [1]

(ii) How much protein is there in 100g of the dried apricots?

.".. 'oo.""oo""'" ""oo""""" .oo...oo... """"oooo "oo"" ""oo oo oo .oooo oooo [1]

"- (b) Preservative E220 is sulphur dioxide.

(I) How does it preserve food?

"OOOO""""" ..oo ""oo"'oo"" .oooO.". ,oO"" [1]

(II) Sulphur dioxide can be made by burning sulphur in air.

Name a source of sulphur.

"oO""" oo..oo.. ""OO"" """'" "oo" oo... ,.. [1]

(Iii) Why is sulphur dioxide used in the manufacture of wood pulp?

.oo """"'OO""""oo""" """"" ..." """'oo""""""""""" oo..., [1]

(c) As part of her project, a pupil was studying dried apricots. She found out that sulphurdioxide 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. Theresulting 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?

. """"""""""'" """"""""'" """"" " """"""'" [2]

(Ii) 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 """"""""'" """"" ." , [1]

Result.. """"""" ""'" """""""" """"""""""""""""""""""""""" [2]

(iii) The hydrogen peroxide oxidised sulphurous acid, a weak acid, to sulphuric acid, astrong acid.

Explain each of the following:

acid " ,.. [2]

weak acid """"""""""""""""""""""""" [1]

strong acid """ [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 inthis solvent.

Describe how you could separate and identify the sugars. which are colourless.

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0

3 (a) An all-metal Viking sword was discovered.

metalhilt

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.

"""""""""""""""""""""""""""""""""" [1]

(II) Suggest a reason why the rusting was greatest near the hilt.

".. ,.........

""""""""""""""""""" [1]

(iii) 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 """""""""""""" [1]

Names of other elements " " [2]

(b) Metals are malleable and can be beaten into the shape of a sword. Why are metalsmalleable?

"""""""""""'" ...................................................

""""""""""""""""'" [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 bedeposits of tin on the surface of the iron.

This experiment could be repeated with different metals. The results of these experimentsare given in the table below.

aqueous solution

iron(ll) chloride

tin(ll) chloride

scandium chloride

mercury(ll) chloride

(i) Complete the table.

iron tin scandium mercury

x

X

./ ......

./ = reaction occurred

)( = no reaction

[1]

(ii) What is the order of reactivity of the four metals?

1 (Most reactive) ,

2

3

.. .....

,...,..............................

4 (Least reactive) .......................................... [2]

(iil) Write a symbol equation for the reaction between scandium atoms and tin(ll) ions, Ascandium ion has a charge of 3+,

. " ."." ".. , , , ', [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 areformed.

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 =

+ 436kJ...190kJ...366kJ

kJ [3]

(II) Calculate the overall energy change for this reaction.

. """"" ..., ..., " ... """'" ., [1]

(III) Is the overall reaction exothermic or endothermic?

.,/

" """"""""'" " [1]

(b) Bromine reacts with alkanes in a similar way to chlorine. Hydrogen bromide is made inthe substitution reaction between propane and bromine.

PROPANE + BROMINE-+- BROMOPROPANE + HYDROGEN BROMIDE

(i) 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.

" """"""""""""""""""'"

. """"'" , [2].

(c) A preparation of the insoluble compound lead(lI) bromide is described below.

To 10cm3 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 filteredand 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 theaqueous lead(lI) nitrate.

... ".. ., ........

. ..., [1]

(iii) Why was it necessary to 'filter and wash'?

.. """"""'" """"""""""""'" ............................................................................

, """""" [2]

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IV

(d) In the experiment, 0.010 mol of lead(lI) nitrate was used and 2.21 g of lead(lI) bromidewere produced.

Calculate the percentage yield of lead(lI) bromide.

" ......

""""""""""'" ......

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5 The table shows some of the elements needed by green plants.

./

)

(a) (I) What element. essential for plant growth, is not mentioned in the table?

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(II) Why is chlorophyll essential for the growth of green plants?)

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..,. """""""" ....

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(III) What are enzymes?

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element taken up useby plant as

nitrogen NO3- or NH4+ to make amino acidsand proteins

magnesium Mg2+ part of chlorophyllmolecule

sulphur. SOi- to make proteincontaining sulphur

potassium K+ making enzymes

(b) When plant material is burnt, an alkaline ash is formed. In Africa, a useful product wasmade 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 inthe fat?

. " ..., """"""""""""""""""""""" [1]

(II) From your answer to (I), give the common name of the product.

. [1]

(c) A shortage of the sulphate ion in plants causeschlorosis, a yellowing of the leaves. Inindustrialcountries,this yellowingis not observeddue to atmosphericpollution.

Suggest an explanation.

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""""""""""""""" """"""""""" ..........................................................

"... , " [3]

(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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, """""""""""""""'" ., """"" """ [2]

(II) What is the name of the linkage common to both proteins and nylon?

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(Iii) What difference in structure is there between protein and nylon?

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. ,.. ,... [2]