4 Chemical Changes - Acids

Question 1

Define acid in terms of pH

Answer 1

A substance with a pH of less than 7

Question 2

Define acids in terms of ions

Answer 2

A substance which releases H+ ions in solution

Question 3

What does (aq) stand for?

Answer 3

Aqueous: when substance is dissolved in water. E.g. NaCl(aq) is salt water

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

Which ions do the common acids form in solution?

Answer 5

HCl forms H+ and Cl-, H2SO4 forms 2H+ and SO4 2-, HNO3 forms H+ and NO3-

Question 6

What is a neutral solution?

Answer 6

A solution with a pH of 7. Water is an example.

Question 7

How do you measure pH?

Answer 7

With an indicator such as universal indicator or pH probe.

Question 8

What is a base?

Answer 8

A metal oxide, hydroxide or carbonate that will react with an acid to produce a salt and water. 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 is a salt?

Answer 11

A compound formed when an acid reacts with a base.
sodium oxide + hydrochloric acid
forms sodium chloride and water

Question 12

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

Answer 12

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

Question 13

What is a neutralisation reaction?

Answer 13

A reaction involving an acid and base that results in a neutral solution

Question 14

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

Answer 14

H+ and OH-

Question 15

Write the equation showing the reaction between H? and OH? ions

Answer 15

H+ + OH- gives H2O

Question 16

metal + acid ?

Answer 16

gives salt + hydrogen gas

Question 17

metal hydroxide + acid ?

Answer 17

gives salt + water

Question 18

metal oxide + acid ?

Answer 18

gives salt + water

Question 19

metal carbonate + acid ?

Answer 19

gives salt + water + carbon dioxide

Question 20

How do you make a soluble salt from an acid?

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What is a strong acid?

Answer 22

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 23

What is a weak acid?

Answer 23

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 24

What is the relationship between the strength of an acid and its pH?

Answer 24

As an acid increases in strength the pH decreases. as the pH increases by 1, the concentration of the acid decreases by
1/10

Question 25

What is a concentrated acid?

Answer 25

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

Question 26

What is a dilute acid?

Answer 26

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

Question 27

How is pH measured?

Answer 27

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