Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2012 Summer Zone 1

Stearic acid is a solid at room temperature. The diagram below shows the apparatus used for finding the melting point of stearic acid. The apparatus was heated at a steady rate and the temperature recorded every minute.

(a) State the name of the piece of apparatus labelled
A, ...............................................................................................................................
B. ............................................................................................................................... [2]
(b) (i) Suggest why the water needs to be kept stirred during this experiment.
...............................................................................................................................
............................................................................................................................... [1]
(ii) Describe a chemical test for water.
test ...............................................................................................................................
result ............................................................................................................................... [2]
(c) A graph of temperature of stearic acid against time of heating is shown below.
[Graph_1]
(i) What was the temperature of the stearic acid after 3 minutes heating?
............................................................................................................................... [1]
(ii) Use the information on the graph to determine the melting point of stearic acid.
............................................................................................................................... [1]
(d) Describe the arrangement and motion of the particles in liquid stearic acid.
arrangement ........................................................................................................................
motion ............................................................................................................................... [2]
(e) A sample of stearic acid contained 1% of another compound with a higher relative molecular mass.
(i) Which one of the following statements about this sample of stearic acid is correct? Tick one box.
□ Its density is exactly the same as that of pure stearic acid.
□ Its boiling point is the same as that of pure stearic acid.
□ Its melting point is different from pure stearic acid.
□ Its melting point is the same as that of pure stearic acid. [1]
(ii) Describe one area of everyday life where the purity of substances is important.
............................................................................................................................... [1]

The diagram below shows the structure of some substances, A, B, C, D and E.

(a) (i) Which one of these substances, A, B, C, D or E, is an element?
.............................................................................................................................. [1]

(ii) What do you understand by the term element?
.............................................................................................................................. [1]

(b) Calculate the relative molecular mass of E.
.............................................................................................................................. [1]

(c) Write the simplest formula for D.
.............................................................................................................................. [1]

(d) Which substance, A, B, C, D or E, conducts electricity when it is molten? Explain your answer.
..............................................................................................................................
.............................................................................................................................. [2]

(e) The equation for the combustion of substance A is shown below.

$$2H_2S + 3O_2 \rightarrow 2H_2O + 2SO_2$$

What type of chemical reaction is this?
Put a ring around the correct answer.
decomposition neutralisation oxidation reversible [1]

Hydrochloric acid and ethanoic acid are both acidic in nature.
(a) Which one of the following is a pH value for an acidic solution.
Put a ring around the correct answer.
pH3 pH7 pH9 pH13 [1]
(b) Describe how you would use litmus to test if a solution is acidic.
.................................................................................................................................
.................................................................................................................................
................................................................................................................................. [3]
(c) Acids react with metal carbonates.
(i) Write a word equation for the reaction of calcium carbonate with hydrochloric acid. [3]
(ii) Calcium carbonate can be used to treat acidic soil.
State one other use of calcium carbonate.
................................................................................................................................. [1]
(iii) Name one other compound that can be used to treat acidic soil.
................................................................................................................................. [1]
(d) Hydrochloric acid reacts with iron to form iron(II) chloride and hydrogen.
Complete the equation for this reaction.
$$ \text{Fe} + ....\text{HCl} \rightarrow \text{FeCl}_2 + ....... $$ [2]

(e) (i) Complete the table below to show:
\(\bullet\) the molecular formula for ethanoic acid
\(\bullet\) the full structural formula for ethanol.


[2]
(ii) Ethanol can be manufactured by the catalytic addition of steam to ethene. Complete the equation for this reaction.
.......... + ......... \rightarrow \text{C}_2\text{H}_5\text{OH} [1]

Fractional distillation is used to separate petroleum into different fractions. Each fraction has a particular use.
(a) Match the fractions on the left with their uses on the right. The first one has been done for you.


(b) Petroleum fractions contain hydrocarbons. What do you understand by the term hydrocarbon?
........................................................................................................................................................................................ [1]

(c) Methane, $CH_4$, is a hydrocarbon.

(i) Draw the structure of methane, showing all atoms and bonds.
........................................................................................................................................................................................ [1]

(ii) Complete the following equation for the burning of methane in excess oxygen.

$CH_4 + .....O_2 \rightarrow .......... + 2H_2O$ [2]

(iii) Methane belongs to a homologous series called the alkanes. What do you understand by the term homologous series?
........................................................................................................................................................................................ ........................................................................................................................................................................................ [2]

(iv) Name the second member of the alkane homologous series.
........................................................................................................................................................................................ [1]

A student investigated the reaction between zinc and hydrochloric acid using the apparatus shown below. The zinc was in excess.
Zinc + hydrochloric acid → zinc chloride + hydrogen

(a) What should the student do to start the reaction? ............................................................................................................................................................. [1]
(b) The student measured the volume of gas in the measuring cylinder at minute intervals. The results are shown in the table.
[Table_1]
time / minutes | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
volume of gas / cm³ | 0 | 15 | 23 | 30 | 33 | 35 | 35 | 35
(i) Plot the results on the grid below and draw the best curve through the points.
[3]
(ii) Explain why the volume of gas stays the same after 5 minutes.
..........................................................................................................................................................
.......................................................................................................................................................... [2]
(c) Complete the following sentences about this reaction using words or phrases from the list below.
concentration, decreases, increases, speed, stays the same, volume
When the ......................... of hydrochloric acid is increased, the volume of gas given off in the first two minutes ......................... . Decreasing the temperature of the reaction mixture ......................... the ......................... of the reaction. [4]
(d) When the reaction is complete, the flask contains a mixture of zinc and aqueous zinc chloride. Describe how you can obtain pure dry crystals of zinc chloride from this reaction mixture.
..........................................................................................................................................................
..........................................................................................................................................................
..........................................................................................................................................................
.......................................................................................................................................................... [3]

Lithium, sodium, and potassium are in Group I of the Periodic Table.
(a) The equation for the reaction of lithium with water is

2Li + 2H$_2$O → 2LiOH + H$_2$

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

(ii) Sodium reacts with water in a similar way to lithium.
Write a symbol equation for the reaction of sodium with water.
[1]

(b) Describe the reactions of lithium, sodium, and potassium with water.
In your description, write about:
• the difference in the reactivity of the metals
• the observations you would make when these metals react with water.
..............................................................................................................
..............................................................................................................
..............................................................................................................
..............................................................................................................
..............................................................................................................
[5]

(c) The diagram below shows an electrolysis cell used to manufacture sodium from molten sodium chloride.


(i) Which letter in the diagram above represents
the anode? .............
the electrolyte? .............
[2]

(ii) State the name of the product formed
at the positive electrode, ...........................................................
at the negative electrode. ...........................................................
[2]

(iii) Which one of the following substances is most likely to be used for the anode?
Put a ring around the correct answer.
graphite iodine magnesium sodium
[1]

(d) Lithium, sodium, and potassium are metals with a low density.
State two other physical properties of these metals.
1. ......................................................................................................
2. ......................................................................................................
[2]

(a) The equations A and B below show two reactions which lead to the formation of acid rain.

A S + O_2 \rightarrow SO_2

B SO_2 + O_3 \rightarrow SO_3 + O_2

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

(ii) Which two of the following statements about reaction B are correct? Tick two boxes.
SO_2 is oxidised to SO_3 [ ]
SO_2 is reduced to SO_3 [ ]
O_3 is reduced to O_2 [ ]
O_3 is oxidised to O_2 [ ] [2]

(iii) Complete the equation to show how an aqueous solution of sulfuric acid, H_2SO_4, is formed from SO_3.
SO_3 + ........ \rightarrow H_2SO_4 [1]

(b) Describe and explain the effect of sulfuric acid on buildings made from limestone (calcium carbonate).
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................ [3]

(c) State one effect of acid rain other than on buildings.
................................................................................................................................................ [1]