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Flashcards in Chemical changes Deck (27)
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1

What pH do acids have?

0-6
(Red-yellow)

2

What pH do alkalines have?

8-14
(Blue-purple)

3

How can you measure the pH of a solution?

Universal indicator
pH probe attached to pH meter (electronically)

4

acid + base ->

salt + water

5

What are titrations used for?

To find out exactly how what volume of acid is needed to neutralise a measured volume of alkali.

6

What happens when an acid ionises in an aqueous solution?

They produce H+ ions

7

What are strong acids?

Acids that ionise completely in water, eg. sulfuric, hydrochloric and nitrate acids. All of the acid particles dissociate to release H+ ions.

8

What are weak acids?

Acids that don't fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions.

9

What happens for each decrease of 1 on the pH scale?

The concentration of H+ ions increases by a factor of 10.

10

What is the difference between the strength and concentration of an acid?

acid strength tells you what proportion of the acid molecules ionise in water
acid concentration measures how much acid there is in a certain volume of water

11

acid + metal oxide ->

salt + water

12

acid + metal hydroxide ->

salt + water

13

acid + metal carbonate ->

salt + water + carbon dioxide

14

acid + metal ->

salt + hydrogen

15

metal + water ->

metal hydroxide + hydrogen

16

What is oxidation?

Loss of electrons

17

What is reduction?

Gain of electrons

18

What is a redox reaction?

A reaction where reduction and oxidation are happening at the same time
(REDuction and OXidation)

19

What is an electrolyte?

a molten/dissolved ionic compound which ions pass through in electrolysis

20

Where will positive ions go in electrolysis?

to the cathode (negative electrode)

21

Where will negative ions go in electrolysis?

to the anode (positive electrode)

22

Why can molten and dissolved ionic compounds electrolyse?

they have free ions and can conduct electricity

23

How can metals be extracted? (two ways)

by being reacted with carbon (if it is less reactive than carbon)
through electrolysis (if it is more reactive than carbon)

24

What are the disadvantages of extracting metals by using electrolysis?

method is very expensive
lots of energy is required (to melt the ore and produce the required current)

25

If a metal is electrolysed in an aqueous solution, what will be produced at the cathode?

if H+ ions are present and the metal is more reactive than hydrogen, hydrogen gas is produced
if the metal is less reactive than hydrogen, a solid layer of the pure metal will be produced instead (and this will coat the cathode)

26

If a metal is electrolysed in an aqueous solution, what will be produced at the anode?

if OH- and halide ions are present, molecules of the halide will be formed
if no halide ions are present, the OH- ions (from the water) will be discharged and oxygen gas (and water) will be formed

27

What do half equations show?

the reaction at one of the electrodes in electrolysis