C2.6 Acids, Bases and Salts

Question 1

What pH does a substance need to be, in order to be acidic?

Answer 1

Under than pH 7

Question 2

What pH does a substance need to be, in order to be a base or an alkali?

Answer 2

Higher than pH 7

Question 3

What pH does substance need to be, in order to be neutral?

Answer 3

7

Question 4

What can be used to test the acidity of substances?

Answer 4

Indicators e.g. universal indicator which gives different colour at different pH values

Question 5

What are examples of products which are acidic? (3)

Answer 5

Car battery acid, vinegar and lemon juice

Question 6

What are examples of products which are alkaline? (3)

Answer 6

Bleach, soap powder and washing-up liquid

Question 7

Besides pH, what else determines weather a substance is acidic or alkali?

Answer 7

The ions it releases when the substance is dissolved in water

Question 8

What ions are released when acids are dissolved in water?

Answer 8

Hydrogen ion - H+(aq)

Question 9

What ions are released when alkalis are dissolved in water?

Answer 9

Hydroxide ions - OH-(aq)

Question 10

What does the state symbol (aq) mean?

Answer 10

Dissolved in water

Question 11

What are the 4 state symbols?

Answer 11

aq, l, g and s

Question 12

What is the word equation for a neutralisation reaction?

Answer 12

acid + base ==> salt + water

Question 13

How can a neutralisation reaction be shown in terms of ions?

Answer 13

H+(aq) + OH-(aq) ==> H2*O(l)

Question 14

What pH are the products from a neutralisation reaction (when an acid neutralises a base)?

Answer 14

They are neutral - they have a pH of 7

Question 15

What is the word equation for reacting a metal with an acid?

Answer 15

acid + metal ==> salt + hydrogen

Question 16

Why is it that not all metals can be used to make salts from reacting it with an acid? (2)

Answer 16

Because some metals are too reactive and will explode in the presence of an acid, and some metals are aren’t reactive enough and won’t produce any salt

Question 17

How can the production of hydrogen be tested?

Answer 17

By using the burning splint test - a lit split at the mouth of a test tube whilst the acid and metal are reacting, will make a ‘squeaky pop’ sound if hydrogen is present, the louder the pop the more hydrogen present

Question 18

What determines the name of a salt, from reacting a metal with an acid?

Answer 18

The first part of the salt is the name of the metal, and the second part of the salt is the from the type of ions present in the acid e.g. hydrochloric acid + magnesium ==> magnesium chloride + hydrogen

Question 19

What are most metal oxide and hydroxides a form of?

Answer 19

Bases - though some are alkalis because they’re soluble in water

Question 20

What is the word equation for the reaction of an acid and a base?

Answer 20

acid + metal oxide or metal hydroxide ==> salt + water

Question 21

What determines the name of a salt, from reacting an acid with a base?

Answer 21

The first part is the metal from the metal oxide(/hydroxide) and the second part is the ions present in the acid e.g. hydrochloric acid + copper oxide ==> copper chloride + water

Question 22

What is produced when ammonia is dissolved in water?

Answer 22

An alkaline solution

Question 23

How can you make a salt from ammonia?

Answer 23

By reacting it with nitric acid

Question 24

What is the word equation for reacting ammonia with nitric acid?

Answer 24

Ammonia + nitric acid ==> ammonium nitrate

Question 25

What salts are soluble?

Answer 25

Most chlorides, sulphates and nitrates - besides, lead chloride, lead sulphate and silver chloride

Question 26

How can you determine what reagents were used to make a particular salt?

Answer 26

By the name of the salt - remember that the salt is named after the acid and the metal, insoluble base or soluble base used to make it

Question 27

What determines what method is used to make a salt?

Answer 27

On whether the reagents used are soluble or insoluble

Question 28

How do you make a soluble salt from a metal or insoluble base? (Insoluble reactant = IR)

Answer 28

1. Add the IR to the acid and stir - it will dissolve in the acid as it reacts
2. Keeping adding the IR until it is in excess - this shows that the acid has been neutralised and the reaction has finished
3. The IR is then filtered out using filter paper and a funnel - the solution left over is a salt solution

Question 29

How do you make a soluble salt with an alkali (soluble base)?

Answer 29

Using the same method as you would with an insoluble base, however you need to use an indicator to see when the solution is neutralised and then repeat this with the same volume of acid and alkali so the salt isn’t contaminated with indicator

Question 30

How can you convert a salt solution into a pure solid crystal?

Answer 30

By using crystallisation

Question 31

How do you carry out crystallisation?

Answer 31

First off all, you heat the solution to evaporate most of the water and make it more concentrated, the left is then left at room temp. to allow the rest of the water to slowly evaporate, and for the salt to crystallise

Question 32

How can you make insoluble salts?

Answer 32

By using a precipitation reaction

Question 33

What is a precipitation reaction?

Answer 33

A reaction where one of the products is insoluble and so forms as a solid precipitate in solution

Question 34

How do you carry out a precipitation reaction?

Answer 34

By mixing two aqueous solutions that contain the ions you need - once the precipitate has formed you can filter out the solution

Question 35

What are other uses of precipitation reactions? (3)

Answer 35

To remove poisonous ions from drinking water, to remove calcium and magnesium ions from water to make it soft, and to remove unwanted ions during the treatment of effluent (sewage)

Question 36

Why are precipitation reactions used?

Answer 36

Because it helps to remove specific ions from a solution