Topic 4 (Chemical Changes)

Question 1

PH Scale goes from

Answer 1

0 to 14

Question 2

0 on the PH scale is

Answer 2

Acidic

Question 3

14 on the PH scale is

Answer 3

Alkaline

Question 4

How can you measure ph

Answer 4

•PH probe
•Indicator

Question 5

What do acids and bases do

Answer 5

Acids and bases neutralise each other.
An acid is a substance with a PH less than 7 and they form H+ ions. An alkali is a base that dissolves in water to form a solution with a PH more than 7 and they form OH- ions. (H+)+(OH-)->H2O

Question 6

Acid + Base ->

Answer 6

Salt + Water

Question 7

What do titrations do

Answer 7

They find out concentration

Question 8

How do you find unknown concentration using titrations

Answer 8

Add a set volume of either alkali to a flask. Add two or three drops of an indicator e.g phenophalene. Fill a burette with an acid with known concentration. Use the burette to add acid to the alkali 1cm^3 at a time giving the flask a regular swirl. When the indicator changes colour stop and see how much acid was required to neutralise the alkali. Then work out concentration of alkali.

Question 9

What is a strong acid

Answer 9

An acid that completely ionises into water

Question 10

What is a weak acid

Answer 10

An acid that only partially ionises in water

Question 11

What is concentration of an acid

Answer 11

How watered down the acid is. You can have a dilute strong acid or a concentrated weak acid they have no correlation.

Question 12

Metal oxides and metal hydroxides are bases what do they form when reacting with an acid

Answer 12

Metal Oxide/Hydroxide+ Acid
-> Salt and Water

Question 13

When a metal carbonate reacts with an acid it produces CO2

Answer 13

Metal Carbonate + Acid
-> Salt+Water+CO2

Question 14

What is the reactivity series

Answer 14

Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper

Question 15

What happens when metals react with acids

Answer 15

Metal + Acid
-> Salt + Hydrogen

Question 16

What is oxidation

Answer 16

The gain of oxygen

Question 17

What is reduction

Answer 17

Loss of oxygen

Question 18

What is oxidation in terms of electrons

Answer 18

Loss of electrons

Question 19

What is reduction in terms of electrons

Answer 19

Gaining electrons

Question 20

What is electrolysis

Answer 20

Splitting up a compound with electricity

Question 21

How does electrolysis work

Answer 21

During electrolysis an electric current passes through an electrolyte. The ions on the electrolyte move towards the electrodes and the compound decomposes. When the ions reach the electrodes they gain or lose electrons to form uncharged atoms and are discharged from the electrodes.

Question 22

Why are some metals extracted using electrolysis

Answer 22

If a metal is too reactive to be displaced by carbon, electrolysis is used to extract it

Question 23

In an aqueous solution as well as the ions from the compound what other ions will be present

Answer 23

H+
OH-
Both from the water

Question 24

In electrolysis of an aqueous solution what goes to the cathode

Answer 24

Whatever element is less reactive, this usually means hydrogen

Question 25

In electrolysis of an aqueous solution what goes to the anode

Answer 25

OH- ions always go to the anode unless halide ions are present