Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2015 Winter Zone 1

(a) The symbols of six particles are shown below.

Na⁺   Ca²⁺   Kr   P   Si   O²⁻

Select from the list of particles to answer the following questions. A particle may be selected once, more than once or not at all.

(i) Which two ions have the same electronic structure? ..................................................... [1]

(ii) Which ion has the same electronic structure as an atom of argon? ............................ [1]

(iii) Which atom can form an ion of the type X³⁻? ................................................................. [1]

(iv) Which atom can form a hydride which has a formula of the type XH₄? .......................... [1]

(b) (i) How many protons, neutrons and electrons are there in one copper(II) ion ⁶⁴₂₉Cu²⁺?

number of protons .....................

number of neutrons .....................

number of electrons .....................

[2]

(ii) ⁴⁵₂₁Sc represents an atom of scandium.

How many nucleons and how many charged particles are there in one atom of scandium?

number of nucleons .....................

number of charged particles .....................

[2]

(c) Two different atoms of sodium are ²³₁₁Na and ²⁴₁₁Na.

(i) Explain why these two atoms are isotopes.

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[2]

(ii) ²⁴₁₁Na is radioactive. It changes into an atom of a different element which has one more proton.

Identify this element.

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[1]

(iii) State two uses of radioactive isotopes.

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[2]

Describe how to separate the following. In each example, give a description of the procedure used and explain why this method works.
(a) Copper powder from a mixture containing copper and zinc powders.
procedure ..........................................................................................................................
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explanation ........................................................................................................................
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(b) Nitrogen from a mixture of nitrogen and oxygen.
procedure ..........................................................................................................................
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explanation ........................................................................................................................
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(c) Glycine from a mixture of the two amino acids glycine and alanine. Glycine has the lower $R_f$ value.
procedure ..........................................................................................................................
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explanation ........................................................................................................................
................................................................................................................................. [2]
(d) Magnesium hydroxide from a mixture of magnesium hydroxide and zinc hydroxide.
procedure ..........................................................................................................................
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explanation ........................................................................................................................
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(a) Sulfur is burned by spraying droplets of molten sulfur into air.

Suggest and explain an advantage of using this method.

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(b) The following equation represents the equilibrium in the Contact process.

$$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$$

Oxygen is supplied from the air.
The composition of the reaction mixture is 1 volume of sulfur dioxide to 1 volume of oxygen.

What volume of air contains 1 dm³ of oxygen?

..................................................................................................................... dm³

(c) Sulfur dioxide is more expensive than air.

What is the advantage of using an excess of air?

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(d) The forward reaction is exothermic. The reaction is usually carried out at a temperature between 400 and 450°C.

(i) What is the effect on the position of equilibrium of using a temperature above 450°C? Explain your answer.

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(ii) What is the effect on the rate of using a temperature below 400°C? Explain your answer.

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(e) A low pressure, 2 atmospheres, is used. At equilibrium, about 98% $SO_3$ is present.

(i) What is the effect on the position of equilibrium of using a higher pressure?

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(ii) Explain why a higher pressure is not used.

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(f) Name the catalyst used in the Contact process.

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(g) Describe how concentrated sulfuric acid is made from sulfur trioxide.

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(a) Synthetic polymers are disposed of in landfill sites and by burning.
(i) Describe two problems caused by the disposal of synthetic polymers in landfill sites.
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(a) (ii) Describe one problem caused by burning synthetic polymers.
..................................................................................................................................................................... [1]

(b) State two uses of synthetic polymers.
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(c) The structural formulae of two synthetic polymers are given below.

(i) Draw the structural formula of the monomer of polymer A.
..................................................................................................................................................................... [2]
(ii) Identify the functional group circled in polymer B.
..................................................................................................................................................................... [1]
(iii) Deduce the two types of organic compound which have reacted to form polymer B.
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(d) Explain the difference between addition and condensation polymers. Classify A and B as either addition or condensation polymers.
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(a) A compound, X, contains 55.85% carbon, 6.97% hydrogen and 37.18% oxygen.
(i) How does this prove that compound X contains only carbon, hydrogen and oxygen?
............................................................................................................................... [1]
(ii) Use the above percentages to calculate the empirical formula of compound X.
............................................................................................................................... [2]
(iii) The $M_r$ of X is 86.
What is its molecular formula?
............................................................................................................................... [2]
(b) (i) Bromine water changes from brown to colourless when added to X.
What does this tell you about the structure of X?
............................................................................................................................... [1]
(ii) Magnesium powder reacts with an aqueous solution of X. Hydrogen is evolved.
What does this tell you about the structure of X?
............................................................................................................................... [1]
(iii) X contains two different functional groups.
Draw a structural formula of X.
............................................................................................................................... [1]

Carbon and silicon are elements in Group IV. They both form oxides of the type XO_2.
(a) Silicon(IV) oxide, SiO_2, has a macromolecular structure.
(i) Describe the structure of silicon(IV) oxide.
[3]
(ii) State three properties which silicon(IV) oxide and diamond have in common.
[3]
(iii) How could you show that silicon(IV) oxide is acidic and not basic or amphoteric?
[2]
(b) Explain why the physical properties of carbon dioxide are different from those of diamond and silicon(IV) oxide.
[1]

The rate of a photochemical reaction is affected by light.

(a) The decomposition of silver bromide is the basis of film photography. This is a redox reaction.

$$2AgBr \rightarrow 2Ag + Br_2$$
cream         black

step 1    $$2Br^- \rightarrow Br_2 + 2e^-$$
step 2    $$Ag^+ + e^- \rightarrow Ag$$

(i) Which step is reduction? Explain your answer.
....................................................................................................................... [1]

(ii) Which ion is the oxidising agent? Explain your answer.
....................................................................................................................... [1]

(b) A piece of white paper was coated with silver bromide and exposed to the light. Sections of the paper were covered as shown in the diagram.

Predict the appearance of the different sections of the paper after exposure to the light and the removal of the card. Explain your predictions.
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(c) Photosynthesis is another example of a photochemical reaction. Green plants can make simple carbohydrates, such as glucose. These can polymerise to make more complex carbohydrates, such as starch.

(i) Write a word equation for photosynthesis.
....................................................................................................................... [2]

(ii) Name the substance which is responsible for the colour in green plants and is essential for photosynthesis.
....................................................................................................................... [1]

(iii) The structural formula of glucose can be represented by H—O—□—O—H .

Draw part of the structural formula of starch which contains two glucose units.

[2]

(iv) Living organisms need carbohydrates for respiration.
What is meant by \textit{respiration}?
....................................................................................................................... [1]