Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2009 Summer Zone 1

(a) Choose from the list of compounds to answer questions (i) to (v).

calcium carbonate carbon dioxide hydrogen chloride iron(III) oxide lead(II) bromide methane sodium hydroxide

Each compound can be used once, more than once or not at all.

Name the compound which

(i) is a transition metal compound,
...................................................................................................................... [1]

(ii) produces brown fumes at the anode when electrolysed,
...................................................................................................................... [1]

(iii) is used to manufacture lime,
...................................................................................................................... [1]

(iv) dissolves in water to form an alkaline solution,
...................................................................................................................... [1]

(v) is the main constituent of natural gas.
...................................................................................................................... [1]

(b) At a high temperature iron(III) oxide is reduced by carbon.

$$\text{Fe}_2\text{O}_3 + 3\text{C} \rightarrow 2\text{Fe} + 3\text{CO}$$

(i) Explain how the equation shows that iron(III) oxide is reduced by carbon.
...................................................................................................................... [1]

(ii) Complete these sentences about the extraction of iron using words from the list.

bauxite blast converter haemetite lime limestone
sand slag

Iron is extracted from .......................................... by mixing the ore with coke and .......................................... in a .......................................... furnace.
The iron ore is reduced to iron and impurities in the ore react with calcium oxide to form .......................................... . [4]

The table shows some observations about the reactivity of various metals with dilute hydrochloric acid.

[Table_1]

(a) Put these metals in order of their reactivity.
most reactive _________________ least reactive
__________________ ________________ ________________ [1]

(b) Zinc is between iron and magnesium in its reactivity. Suggest what observations are made about how fast the bubbles are produced when zinc reacts with dilute hydrochloric acid.
.................................................................................................................... [1]

(c) Magnesium is extracted by the electrolysis of molten magnesium chloride.



(i) What information in the diagram suggests that magnesium is less dense than molten magnesium chloride?
.................................................................................................................... [1]

(ii) Suggest why magnesium has to be extracted by electrolysis rather than by heating its oxide with carbon.
.................................................................................................................... [1]

(iii) Suggest why a stream of inert gas is blown over the surface of the molten magnesium.
.................................................................................................................... [1]

(iv) State the name of a gaseous element which is inert.
.................................................................................................................... [1]

(d) In some old magnesium manufacturing plants, coal gas is blown over the surface of the magnesium. The list shows the main substances in coal gas.

carbon monoxide ethene hydrogen
hydrogen sulfide methane

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

(ii) Suggest two hazards of using coal gas by referring to two specific substances in the list.
substance
....................................................................................................................
hazard
....................................................................................................................
substance
....................................................................................................................
hazard
.................................................................................................................... [2]

(e) Carbon monoxide can be removed from coal gas by mixing it with steam and passing the mixture over a catalyst of iron(III) oxide at 400°C.

$\text{CO + H}_2\text{O} \rightleftharpoons \text{CO}_2 + \text{H}_2$

(i) Write a word equation for this reaction.
.................................................................................................................... [1]

(ii) What does the symbol $\rightleftharpoons$ mean?
.................................................................................................................... [1]

(iii) Iron(III) oxide reacts with acids to form a solution containing iron(III) ions. Describe a test for aqueous iron(III) ions.
test
....................................................................................................................
result
.................................................................................................................... [2]

Petroleum is a mixture of hydrocarbons which can be separated into fractions such as petrol, paraffin and diesel.
(a) State the name of the process used to separate these fractions.
................................................................................................................................. [1]
(b) Name \textbf{two} other fractions which are obtained from petroleum.
..................................................... and ............................................................ [2]
(c) Give \textbf{one} use for the paraffin fraction.
................................................................................................................................. [1]
(d) Many of the compounds obtained from petroleum are alkanes. Which \textbf{two} of the following structures are alkanes?


................................................................................................................................. [1]
(e) Use words from the list below to complete the following sentence.

\textit{ethane} \textit{ethene} \textit{hydrogen} \textit{nitrogen} \textit{oxygen} \textit{reactive} \textit{unreactive} \textit{water}

Alkanes such as ................................... are generally ..................................... but they can be burnt in .................................... to form carbon dioxide and ..................................... [4]
(f) Alkanes are saturated hydrocarbons. What do you understand by the terms:
(i) saturated,
..................................................................................................................................
..................................................................................................................................
(ii) hydrocarbon?
.................................................................................................................................
.................................................................................................................................. [2]

This question is about some compounds of nitrogen.
A mixture of ammonium sulfate and sodium hydroxide was warmed in a test-tube. The gas was tested with moist red litmus paper.

(a) State the name of the gas released.
...................................................................................................... [1]
(b) State the colour change of the litmus paper.
...................................................................................................... [1]
(c) Complete the word equation for the reaction of ammonium carbonate with hydrochloric acid.
ammonium carbonate + hydrochloric acid → ... + ... + ...
........................ .............................................. [3]
(d) Ammonium salts such as ammonium nitrate, $\text{NH}_4\text{NO}_3$ and ammonium chloride $\text{NH}_4\text{Cl}$ are used as fertilisers.
(i) Explain why farmers need to use fertilisers.
......................................................................................................
...................................................................................................... [1]
(ii) Explain why ammonium nitrate is a better fertiliser than ammonium chloride.
...................................................................................................... [1]
(iii) Calculate the relative formula mass of ammonium nitrate.
...................................................................................................... [1]
(e) When ammonium nitrate is heated nitrogen(I) oxide is given off.
Nitrogen(I) oxide relights a glowing splint. Name one other gas which relights a glowing splint.
...................................................................................................... [1]
(f) State one harmful effect of nitrogen oxides on the environment.
...................................................................................................... [1]

A student used the apparatus shown below to investigate the rate of reaction of calcium carbonate with dilute hydrochloric acid.

CaCO_3 + 2HCl \rightarrow CaCl_2 + CO_2 + H_2O



(a) Use the information in the equation to suggest why the mass of the flask and contents decreases with time.
..............................................................................................................................................
.............................................................................................................................. [1]

(b) The graph shows how the mass of the flask and its contents changes with time.


(i) At what time was the reaction just complete?
.............................................................................................................................................. [1]

(ii) On the graph, mark with an X the point where the speed (rate) of reaction was fastest. [1]

(iii) The student repeated the experiment but altered the concentration of the hydrochloric acid so that it was half the original value. In both experiments calcium carbonate was in excess and all other conditions were kept the same.
On the graph on page 10, draw a curve to show how the mass of the flask and contents changes with time when hydrochloric acid of half the concentration was used. [2]

(c) How does the speed (rate) of this reaction change when

(i) the temperature is increased, ....................................................................................... [1]

(ii) smaller pieces of calcium carbonate are used? ..................................................... [1]

(d) Complete the following sentence using words from the list.

combustion expansion large rapid slow small

In flour mills there is often the risk of an explosion due to the rapid .......................................... of the very .......................................... particles which have a very .......................................... surface area to react. [3]

(e) Cells in plants and animals break down glucose to carbon dioxide and water.

glucose + oxygen \rightarrow carbon dioxide + water

(i) State the name of this process.
.............................................................................................................................................. [1]

(ii) In this process enzymes act as catalysts. What do you understand by the term catalyst?
.............................................................................................................................................. [1]

Bromine is an element in Group VII of the Periodic Table.
(a) Write the formula for a molecule of bromine.
.................................................................................................................................................. [1]
(b) Complete the diagram below to show the arrangement of the molecules in liquid bromine.
represents a bromine molecule

[2]
(c) A teacher placed a small amount of liquid bromine in the bottom of a sealed gas jar of air. After two minutes brown fumes were seen just above the liquid surface. After one hour the brown colour had spread completely throughout the gas jar.

Use the kinetic particle theory to explain these observations.
.................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. [3]
(d) Magnesium salts are colourless but Group VII elements are coloured.
An aqueous solution of magnesium bromide reacts with an aqueous solution of chlorine.
magnesium bromide + chlorine → magnesium chloride + bromine
State the colour change in this reaction.
.................................................................................................................................................. [2]
(e) A solution of magnesium bromide will not react with iodine.
Explain why there is no reaction.
.................................................................................................................................................. [1]
(f) The structures of some compounds containing bromine are shown below.

(i) Write the simplest formula for the substance with structure A.
.................................................................................................................................................. [1]
(ii) State the name of the substance with structure D.
.................................................................................................................................................. [1]
(iii) State the type of bonding within a molecule of structure C.
.................................................................................................................................................. [1]
(iv) Which two structures are giant structures?
............................................................... and ............................................................... [1]
(v) Why does structure A conduct electricity when it is molten?
.................................................................................................................................................. [1]

Hydrogen chloride can be made by burning hydrogen in chlorine.

(a) Complete the equation for this reaction.

$H_2 \ + \ \text{..............} \rightarrow \ \text{..............} \ HCl$ [2]

(b) Draw a dot and cross diagram for a molecule of hydrogen chloride. Show all the electrons.

use o for an electron from a hydrogen atom
use x for an electron from a chlorine atom

[2]

(c) Hydrochloric acid is formed when hydrogen chloride gas dissolves in water. Suggest the pH of hydrochloric acid.
Put a ring around the correct answer.

$\text{pH 1 \ \ pH 7 \ \ pH 9 \ \ pH 13}$ [1]

(d) Complete the equation for the reaction of hydrochloric acid with zinc.

$\text{zinc \ + \ hydrochloric acid \rightarrow \ zinc chloride \ + \ .................}$ [1]

(e) Describe how dry crystals of zinc chloride can be obtained from a solution of zinc chloride.

...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................

[2]

(f) A student electrolysed molten zinc chloride.
State the name of the product formed at

(i) the anode, .............................................................................................................................. [1]

(ii) the cathode. ........................................................................................................................... [1]