Chemical reactions

Question 1

(3) Write the balanced equation for water decomposing to form hydrogen and
oxygen.

Answer 1

2H2O → 2H2 + O2
• reactant formula (1)
• product formulae (1)
• balancing correct formulae
(1)

Question 2

(2) Describe the test to show that a gas is hydrogen.

Answer 2

lighted splint
gas burns( 1)
• with (squeaky) pop (if air
present) (1)

Question 3

(2) Describe the test to show that a gas is oxygen.

Answer 3

glowing splint (1)
• relights (1)

Question 4

(1) Seawater can also be decomposed using electrolysis.
Seawater is sodium chloride solution.
When this is decomposed one product is a toxic gas.
The toxic gas produced is

Answer 4

chlorine

Question 5

(1) Give a safety precaution that should be taken when collecting this toxic gas.

Answer 5

use a fume cupboard/open all the
windows /(good) ventilation/wear a
gas mask

Question 6

(1) When dilute hydrochloric acid reacts with copper oxide one of the products is

Answer 6

copper chloride

Question 7

(2) Explain what is meant by electrolysis.

Answer 7

decomposition /break
down of {compound /
substance / electrolyte}(1)
• using electricity / electrical
energy / d.c supply (1)

Question 8

(3) Chlorine gas reacts with sodium hydroxide solution to form sodium chlorate(I), NaOCl, sodium chloride and water
Write the balanced equation for this reaction

Answer 8

reactant formulae (1)
• product formulae (1)
• balancing correct formulae
(1)

Question 9

(1) Sodium chloride solution can be prepared by reacting sodium hydroxide solution
with an acid.
Give the name of the acid that must be used.

Answer 9

hydrochloric (acid)

Question 10

(1) Which row of the table correctly identifies chalk, marble and limestone as
sedimentary or metamorphic rocks?

Answer 10

sedimentary / metamorphic /

sedimentary

Question 11

(2) Suggest how you could show that, when calcium carbonate is heated, a
reaction takes place.

Answer 11

{find mass of / weigh} solid before
heating (1)
• (heat in a suitable container) and
{find mass / weigh} again (when
cool) (1)

Question 12

(2) Describe what you would observe when water is added, one drop at a time, to
cold calcium oxide

Answer 12

fizzing / hissing (1)
• steam (1)
• swells (1)
• solid crumbles (to a powder) (1)
• becomes hot (1)

Question 13

(2) Write the balanced equation for the reaction of calcium hydroxide with
carbon dioxide

Answer 13

Ca(OH)2 + CO2 → CaCO3 + H2O

Question 14

(1) State the common name for calcium hydroxide solution.

Answer 14

limewater

Question 15

(2) Explain why calcium carbonate removes acidic gases from emissions in power
station chimneys.

Answer 15

(calcium carbonate) reacts with
{acidic gases / sulphur dioxide} (1)
• (because) calcium carbonate is a
base (1)
• to form a salt / calcium sulfate (1)
• neutralisation (reaction) (1)

Question 16

(1) State a hazard associated with chlorine gas.

Answer 16

toxic / poisonous (gas)

Question 17

(2) Describe a test that can be used to identify a sample of gas as chlorine.

Answer 17

(damp blue) litmus (paper)
(1)
• (turns red then) white /
bleaches (1)

Question 18

(1) State a use of chlorine.

Answer 18

making {poly(chloroethene / PVC /
solvents / medicines / agrochemicals /
disinfectants}
bleach / sterilising water / killing
bacteria

Question 19

(2)sodium chloride solution is electrolysed.
………….. NaCl + ………….. H2
O ……………………………… + ……………………………… + ………………………………

Answer 19

2NaCl + 2H2O → 2NaOH + H2

+ Cl2

Question 20

(6) Use these results of electrolysis to compare the volumes of hydrogen and oxygen
formed and to show the effect of changing the time and the current on the
volumes of these gases.

Answer 20

Comparing volumes of hydrogen and oxygen
• (in each experiment) volume of hydrogen is twice volume of
oxygen
• because water molecules contain twice as many hydrogen
atoms as oxygen atoms / is H2O
• overall 2H2O → 2H2 + O2
Relating volumes of gases to current and time
• (from experiments 1 and 2) time doubles
• (from experiments 1 and 2) volumes of gases double
• Volumes of gases are directly proportional to the time for
electrolysis / passage of current
• (from experiments 1 and 3) as current x 1.5
• (from experiments 1 and 3) volumes of gases x 1.5
• volumes of gases are directly proportional to the current

Question 21

(1) Sodium chloride solution can be prepared by reacting sodium hydroxide solution
with an acid.
Give the name of the acid that must be used.

Answer 21

hydrochloric (acid)

Question 22

(1) State the form of energy used to carry out the electrolysis

Answer 22

electrical (energy) / electricity /

direct (electric) current

Question 23

(1) Name the gas formed at the other electrode.

Answer 23

hydrogen

Question 24

(2) Describe the test to show that a gas is chlorine.

Answer 24

(damp blue or red) litmus (paper)

((turns red and) bleached / white

Question 25

(1) Which of these can be used to obtain chlorine from sea water?

Answer 25

electrolysis

Question 26

(1) acid + metal carbonate salt + water + ..........................................................................................

Answer 26

carbon dioxide

Question 27

(2) CuO + .............. HCl CuCl2= + ............................

Answer 27

CuO + 2 HCl → CuCl2 + H2O

Question 28

(1) An acid reacts with a metal oxide to form

Answer 28

a salt and water only

Question 29

(2) State two things you would see when solid copper carbonate reacts with dilute nitric acid.

Answer 29

``` (acid) colourless (liquid/solution) (1) • (carbonate) green (solid) (1) • disappears (1) • effervesces/fizzes/bubbles (1) • blue (solution) (forms) (1) ```

Question 30

(3) Write the balanced equation for the reaction of copper carbonate with dilute nitric acid

Answer 30

CuCO3 + 2HNO3 → Cu(NO3)2 + H20 + CO2

Question 31

(2) Explain what is meant by electrolysis

Answer 31

``` decomposition (of compound/substance) (1) M1 • (by) (direct electric) current (1) M2 ```

Question 32

(2) Describe a test to show the gas is oxygen.

Answer 32

``` glowing splint (1) M1 • relights (1) M2 ```

Question 33

(2) Explain what is meant by electrolysis

Answer 33

decomposition (of compound/substance /electrolyte)(1) • using (direct) current (1)

Question 34

(2) Describe the test to show that a gas is chlorine.

Answer 34

(damp blue) litmus (paper) (1) • (turns red then) {bleaches / goes white} (1)

Question 35

(1) C6H9Cl3 | State the name of the polymer

Answer 35

poly(chloroethene)

Question 36

(1) The reaction produces silver chloride as a precipitate. | In an equation this would be shown as

Answer 36

AgCl(s)

Question 37

(1) The total mass of this apparatus was measured. The flask was shaken to allow the silver nitrate solution and dilute hydrochloric acid to react. After the reaction the total mass of the apparatus was measured again. State how the total mass of the apparatus after the reaction will compare with the total mass of the apparatus before the reaction.

Answer 37

same/no change

Question 38

(2) Write the balanced equation for the reaction of silver nitrate solution, AgNO3 , with dilute hydrochloric acid to form silver chloride, AgCl, and nitric acid.

Answer 38

HCl + AgNO3 → AgCl + HNO3

Question 39

(1) Dilute sulfuric acid was added to magnesium oxide. | State the name of the salt formed.

Answer 39

magnesium sulphate