Paper 1 - Chemical changes

Question 1

Acid

Answer 1

Acids produce hydrogen ions (H+
) in aqueous solutions. They have a pH range of 0-6.

Question 2

Alkali:

Answer 2

: Alkalis produce hydroxide ions (OH-
) in aqueous solutions. They have a pH range of
8-14.

Question 3

Crystallisation

Answer 3

A separation technique used to produce solid crystals from a solution by
evaporating the solvent.

Question 4

Displacement

Answer 4

: A chemical reaction in which a more reactive element displaces a less
reactive element from its compound.

Question 5

Electrolysis

Answer 5

: The splitting up of an ionic compound using electricity. The electric current is
passed through a substance causing chemical reactions at the electrodes and the
decomposition of the materials.

Question 6

Electrolyte

Answer 6

A solution containing free ions from the molten or dissolved ionic substance.
The ions are free to move to carry charge.

Question 7

Extraction:

Answer 7

Extraction techniques are used to separate a desired substance when it is mixed
with others.

Question 8

Filtration

Answer 8

A separation technique used to separate solids from liquids.

Question 9

Negative electrode

Answer 9

It is where positively charged ions gain
electrons and so the reactions are reductions.

Question 10

Neutralisation

Answer 10

The reaction when an acid and a base react to form water and a salt.

Question 11

Oxidation

Answer 11

A reaction involving the gain of oxygen. Oxidation is the loss of electrons.

Question 12

pH scale:

Answer 12

: The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution,
and can be measured using universal indicator or a pH probe.

Question 13

Positive electrode

Answer 13

. It is where negatively charged ions
lose electrons and so the reactions are oxidations.

Question 14

*Redox reaction

Answer 14

: A reaction in which both oxidation and reduction occur simultaneously

Question 15

Reduction

Answer 15

. Reduction is the gain of electrons.

Question 16

Reduction with carbon

Answer 16

Metals less reactive than carbon can be extracted from their oxides
by reduction with carbon.

Question 17

Strong acid:

Answer 17

A strong acid is completely ionised in aqueous solution. Examples of
strong acids are hydrochloric, nitric and sulfuric acids.

Question 18

The reactivity series

Answer 18

Metals are arranged in order of their reactivity in a reactivity series.
This can be used to predict products from reactions.

Question 19

Universal indicator

Answer 19

: A mixture of dyes that changes colour gradually over a range of pH and
is used in testing for acids and alkalis.

Question 20

Weak acid:

Answer 20

A weak acid is only partially ionised in aqueous solution. Examples of
weak acids are ethanoic, citric and carbonic acids

Question 21

what is oxidation/reduction

Answer 21

oxidation - when a substance gains electrons
reduction - when a substance loses oxygen

Question 22

what is the reactivity series of metals ? what are the trends in reactivates of metals in reactions with acids / water

Answer 22

the series shows the metal in order of their activity
metals above H2 in reactivity series react with acid to produce H2 .The more reactive the metal is , the quicker and more violent reaction with acid occurs.
Metals below H2 don’t react with acids .
Not all metals above H2 react with water .

Question 23

what is displacement reaction ?

Answer 23

a reaction where a more reactive metal displaces a less reactive metal from a compound.

Question 24

how can metals less reactive than carbon be extracted ?

Answer 24

reduction with carbon. Carbon displaces the metal in metal oxide - gets oxidised to carbon oxides .Metal from the metal oxide gets reduced to the pure metal .

Question 25

how are metals more reactive than carbon extracted ?

Answer 25

by electrolysis

Question 26

what is the equation for a reaction between metals and acids ? what type of reaction in this ?

Answer 26

metal + acid —> salt + hydrogen
displacement reaction

Question 27

which metals in the reactivity series will react with acid

Answer 27

those above hydrogen

Question 28

what is the general equation for a neutralisation equation?

Answer 28

base + acid —>salt + water

Question 29

how is soluble salt formed ?

Answer 29

1) react the excess acid with some insoluble chemical
2) filter the leftovers
3) crystallise the product

Question 30

what do acids and alkalis produce in the aqueous solutions ?

Answer 30

acids produce hydrogen ions , alkalis produce hydroxide ions

Question 31

what are bases , acids and alkalis ?

Answer 31

bases are compounds that neutralise acids , acids produce hydrogen ions in aqueous solution , alkalis are soluble bases - produce hydroxide ions in aqueous solution

Question 32

what is the pH scale and what does a pH of 7 show ?

Answer 32

The measure of acidity / alkalinity of a solution ; neutral solution

Question 33

what is electrolysis ?

Answer 33

the passing of an electric current through ionic substances that are molten or in solution to break them down into elements ; ions are discharged at electrons to produce these

Question 34

what is an electrolyte?

Answer 34

the liquid / solution which conducts electricity

Question 35

what is a cathode and what is an anode?

Answer 35

cathode is the negative electrode , anode is the positive electrode

Question 36

what occurs at the cathode and what occurs at the anode during electrolysis?

Answer 36

reduction occurs at the cathode
oxidation occurs at the anode

Question 37

in aqueous electrolysis , which element is discharged at the cathode ? oxygen is produced at the anode unless what ?

Answer 37

the less reactive element discharges at the cathode . Hydrogen is produced unless there is a less reactive metal , in which case the said metal is produced . Oxygen is produced at the anode unless the solution contains halide ions , in which case halogen molecules are produced .

Question 38

how is aluminium manufactured ? why is it expensive ?

Answer 38

aluminium is made through electrolysis of aluminium oxide and cryolite .
Lots of energy is needed to produce the current in electrolysis which makes this process expensive .