Section 3 - Chemical changes - Acids, bases, strength of acids, soluble and insoluble salts

Question 1

What do acids and alkalis form in water?

Answer 1

Acids form H+ ions

Alkalis form OH- ions

Question 2

What does pH scale measure?

Answer 2

How acidic or alkaline a solution is

Question 3

What is a base?

Answer 3

A substance that reacts with an acid to produce a salt and water. An alkali is a base that is soluble in water

Question 4

3 types of indicators and colours they each go when in acidic, neutral and alkaline solutions?

Answer 4

Litmus - red in acidic, purple in neutral, blue in alkaline
Methyl orange - red in acidic, yellow in neutral and alkaline
Phenolphthalein - Colourless in acidic or neutral, and pink in alkaline

Question 5

What is neutralisation and what does it produce? Are the products acidic, neutral or alkaline?

Answer 5

Reaction between an acid and a base, producing a salt and water. Products are neutral with pH7

Question 6

Ionic equation for neutralisation reactions in aqueous solutions?

Answer 6

H+ (aq) + OH- (aq) –> H2O (l)

Question 7

What happens when acids ionise (or dissociate) in solution?

Answer 7

Split up to produce a hydrogen ion and another ion

Question 8

Which out of strong and weak acids ionise completely in water?

Answer 8

Strong acids ionise almost completely in water

Weak acids do not fully ionise in solution

Question 9

What type of reaction is the ionisation of a weak acid?

Answer 9

Reversible reaction, which sets up an equilibrium as equilibrium is to the left

Question 10

What does acid strength tell you?

Answer 10

What proportion of the acid molecules ionise in water

Question 11

What does concentration of an acid measure? What is it measured in?

Answer 11

Measures how much acid there is in a litre of water. Concentrated or dilute
Measured in g dm-3 or mol dm-3

Question 12

If the concentration of H+ ions increases by a factor of 10, what happens to the pH?

Answer 12

pH decreases by 1

Question 13

Two equations for when an acid react with a base?

Answer 13

Acid + metal oxide –> salt + water

Acid + metal hydroxide –> salt + water

Question 14

3 ways salts are formed when acid reacts with what?

Answer 14

Acid reacts with base, metal or metal carbonate

Question 15

Equations for when acid reacts with a metal and metal carbonate each?

Answer 15

Acid + metal –> salt + hydrogen

Acid + metal carbonate –> salt + water + carbon dioxide

Question 16

How can you test for hydrogen gas?

Answer 16

Collect gas in test tube and put lighted splint in. If there is a squeaky pop noise, hydrogen is present

Question 17

How can you test for carbon dioxide?

Answer 17

Bubble the gas through limewater. If limewater turns cloudy, carbon dioxide is present

Question 18

Are common salts of sodium, potassium and ammonium soluble or insoluble?

Answer 18

Soluble

Question 19

Are nitrates soluble or insoluble?

Answer 19

Soluble

Question 20

Are common chlorides soluble or insoluble?

Answer 20

Soluble (except silver- and lead- chloride)

Question 21

Are common sulfates soluble or insoluble?

Answer 21

Soluble (except lead-, barium- and calcium- sulfate)

Question 22

Are common carbonates and hydroxides soluble or insoluble?

Answer 22

Insoluble (except for sodium, potassium and ammonium ones)

Question 23

How can you make a pure, dry sample of an insoluble salt? What type of reaction?

Answer 23

Use a precipitation reaction. React a soluble salt that contains one of the ions you want in the salt with a soluble salt that contains the other ion you need
e.g. to make lead chloride, mix lead nitrate and sodium chloride

Question 24

2 ways you can make a soluble salt?

Answer 24

React an acid that contains one of the ions you want in the salt with an insoluble base that contains the other ion you need
Reacting an acid with an alkali, but acid has to be neutralised