Chemical Changes

Question 1

What is an alkali

Answer 1

A base that is soluble in water where the concentration of OH- is high(er)

Question 2

What colours does litmus go

Answer 2

Red in acidic solutions
Purple in neutral solutions
Blue in alkaline solutions

Question 3

What colours does methyl orange go

Answer 3

Red in acidic solutions
Orange in neutral Yellow in alkaline solutions

Question 4

What colours does phenolphalein go

Answer 4

Colourless in acidic or neutral solutions
Pink in alkaline solutions

Question 5

What is reaction between an acid and base called

Answer 5

Neutralisation

Question 6

What do strong acids do in water

Answer 6

Fully (or close to) dissociate

Question 7

What do weak acids do in water

Answer 7

Partially dissociate

Question 8

How much does pH increase by

Answer 8

A factor of 10

Question 9

What forms when an acid reacts with a metal (hydr)oxide

Answer 9

Salt + water

Question 10

What forms when an acid reacts with a metal

Answer 10

Salt + Hydrogen

Question 11

What forms when an acid react with a metal carbonate

Answer 11

Salt + Water + Carbon dioxide

Question 12

How to test for CO2

Answer 12

bubble the gas through limewater and if present the limewater will turn cloudy then colourless again

Question 13

Solubility rules

Answer 13

All sodium, potassium and ammonium salts are soluble

All nitrates are soluble

Most chlorides (except silver and lead) are soluble

Most sulphates (except lead, barium and calcium) are soluble

Most carbonates and hydroxides (except sodium, potassium and ammonium) are insoluble

Question 14

What happens when an acid reacts with ammonia

Answer 14

An ammonium salt is formed

Question 15

How to to make an soluble salt from an insoluble base

Answer 15

Excess base method

This cannot be used to make sodium, potassium and ammonium salts

Question 16

Excess base method

Answer 16

Use the metal oxide and corresponding acid

eg. to make copper sulfate crystals use copper oxide + sulfuric acid

Add some of the acid to a beaker and then add excess base to ensure that all of the acid has been used up

Gently warm

Filter then evaporate

Question 17

What is the titration method used for

Answer 17

Making sodium, potassium and ammonium salts which are inseparable by filtration

Question 18

Titration method

Answer 18

Choose suitable chemicals
Alkaline + corresponding acid (similar to excess base)

Use glass pipette to place 25.0 cm ^3 of alkali into a conical flask

Add a few drops of phenolphthalein (it will turn pink)

Put the acid into the burette and add to the alkali a bit at a time + swirl

Measure where indicator goes colourless

Repeat and be careful + adjust volume

Heat the mixture and evaporate water

Leave to crystallise

Filter

Question 19

What is the precipitation method used for

Answer 19

To make insoluble salts and when both base and salt are solids

Question 20

Precipitation method

Answer 20

Use the metal nitrate and the sodium compound

eg. Barium nitrate and sodium sulfate to make barium sulfate

Mix the two solutions together in a beaker

Filter

Wash with distilled water

Leave to dry

Question 21

What is a precipitate

Answer 21

A solid made from reacting two solutions together

Question 22

What happens to the cations in electrolysis

Answer 22

reduction

Question 23

What happens to the anions in electrolysis

Answer 23

oxidised

Question 24

How to set up an electrochemical cell

Answer 24

2 inert electrodes (usually graphite)

Clean the surfaces using emery paper

Place into a beaker

Connect to a power supply using crocodile clips and wires

Question 25

What is formed at the cathode

Answer 25

Hydrogen gas
OR
If less reactive metal than hydrogen is present that will be formed

Question 26

What is formed at the anode

Answer 26

Oxygen
OR
Halides if they are present

Question 27

What is the half-equation at the anode is oxygen is formed

Answer 27

4OH- –> O2 + 2H2O +4e-