CC8 Acids

Question 1

What does soluble mean? What does insoluble mean?

Answer 1

Dissolves in water. Does not dissolve in water

Question 2

Define acid in terms of pH

Answer 2

A substance with a pH of less than 7

Question 3

Define acids in terms of ions

Answer 3

A substance which releases H⁺ ions in solution

Question 4

State the three common acids and give their formulae

Answer 4

Hydrochloric acid, HCl(aq), Sulphuric acid, H₂SO₄(aq), Nitric acid, HNO₃

Question 5

Define pH in terms of ions

Answer 5

Below pH 7 the lower the pH the higher the concentration of H+ ions. Above pH 7 the higher the pH the higher the concentration of OH- ions

Question 6

What is a neutral solution?

Answer 6

A solution with a pH of 7. It has the same concentration of H+ and OH- ions. Water is an example.

Question 7

How do you measure pH?

Answer 7

With an indicator or pH probe.

Question 8

What is a base?

Answer 8

A metal oxide, hydroxide or carbonate that will neutralise an acid. E.g. copper oxide

Question 9

What is an alkali?

Answer 9

A soluble base. E.g. sodium hydroxide

Question 10

Which ions are always present in a solution of an alkali?

Answer 10

OH⁻

Question 11

What type of salts are formed by the three main acids?

Answer 11

Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates

Question 12

What causes some metals not to completely react with an acid?

Answer 12

A layer of the salt produced (which is insoluble) formed on the surface of the metal blocking the acid from the metal

Question 13

What is a precipitate?

Answer 13

A product formed from a chemical reaction of two liquids that is solid

Question 14

What do you see if a precipitate forms?

Answer 14

turn cloudy, see the solid particles

Question 15

What do you see if carbon dioxide or hydrogen is formed?

Answer 15

bubbles/ effervescence because they are gasses

Question 16

What is a neutralisation reaction?

Answer 16

A reaction involving an acid that results in a neutral solution.

Question 17

Write an ionic equation for neutralisation.

Answer 17

H⁺ + OH⁻ → H₂O

Question 18

Which ions always react together in a neutralization reactions between acids and alkalis?

Answer 18

H⁺ and OH⁻

Question 19

metal + acid →

Answer 19

→ salt + hydrogen gas

Question 20

metal hydroxide + acid →

Answer 20

→ salt + water

Question 21

metal oxide + acid →

Answer 21

→ salt + water

Question 22

metal carbonate + acid →

Answer 22

→ salt + water + carbon dioxide

Question 23

How do you make a soluble salt from an acid?

Answer 23

React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid

Question 24

If a salt is in solution, how do you extract it as a solid?

Answer 24

Allow the water to evaporate off and it will leave the salt behind as a solid.

Question 25

What is a strong acid?

Answer 25

An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻.

Question 26

What is a weak acid?

Answer 26

An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.

Question 27

What is the relationship between an acid of pH2 and an acid of pH 3?

Answer 27

pH 2 is 10 times more hydrogen ions than pH 3

Question 28

What is a concentrated acid?

Answer 28

An acid where there are lots of acid particles in the water.

Question 29

What is a dilute acid?

Answer 29

An acid where there are fewer acid particles in the water.

Question 30

How is pH measured?

Answer 30

pH is related to the concentration of H⁺ in a solution.

Question 31

How can hydrogen be tested for?

Answer 31

Makes a squeaky pop when a splint is placed in it

Question 32

How can carbon dioxide be tested for?

Answer 32

Bubble through limewater, turns it milky (cloudy)

Question 33

What salt makes a blue solution?

Answer 33

Copper sulfate

Question 34

What colour is litmus in acid and alkali?

Answer 34

Acid – red, alkali – blue

Question 35

What colour is methyl orange in acid and alkali?

Answer 35

Acid – red, alkali – yellow

Question 36

What colour is phenol phthalein in acid and alkali?

Answer 36

Acid – colourless, alkali – pink

Question 37

How do you prepare a sample of a soluble salt from an insoluble base and an acid?

Answer 37

Neutralisation with excess insoluble base, filtration, crystallisation

Question 38

How do you prepare a sample of a soluble salt from an acid and an alkali?

Answer 38

Titration, repeat titration without indicator, crystallisation

Question 39

How do you prepare a sample of an insoluble salt from two solutions

Answer 39

Combine, filtration, rinse with distilled water, dry

Question 40

What colour is copper sulphate solution?

Answer 40

blue