Year 9 - Acids and Alkalis

Question 1

what is an acid?

Answer 1

• reacts with bases to form a neutral solution
• when dissolved (dissociated) in water forms hydrogen (H⁺) ions (proton donor)
(eg. HCl —> H⁺ +Cl⁻)

Question 2

what is a base?

Answer 2

• a substance that will react with an acid to form a neutral solution

Question 3

what is an alkali?

Answer 3

• when dissolved (dissociated) in water, an alkali will increase the concentration of hydroxide (OH⁻) ions

Question 4

what substances are bases?

Answer 4

• metal oxides; eg. copper (II) oxide, iron (II) oxide
• metal hydroxides; eg. potassium hydroxide
• metal carbonates; eg. sodium carbonate
• ammonia

Question 5

what is the difference between an alkali and a base?

Answer 5

• all alkalis are bases but not all bases are alkalis

- alkalis are soluble bases

Question 6

pH 0-3

dark red, red, pink, orange

Answer 6

• strong acid

Question 7

pH 4-6

dark yellow, yellow, yellow green

Answer 7

• weak acid

Question 8

pH 7

green

Answer 8

• neutral

Question 9

pH 8-10

dull green, dark green, green blue

Answer 9

• weak alkali

Question 10

pH 11-14

blue, darker blue, dark blue, purple

Answer 10

• strong alkali

Question 11

what is Universal Indicator (UI)?

Answer 11

• also known as Full Range Indicator
• a mixture of indicators
• ranges from 0-14
• tells us how acidic or alkaline a substance is by which colour it has turned

Question 12

H⁺ + OH⁻ =

Answer 12

• H₂O

Question 13

litmus paper turns _____ in acids

Answer 13

• red

Question 14

litmus paper turns _____ in alkalis

Answer 14

• blue

Question 15

red litmus paper stays _____ in neutral substances, but blue litmus paper stays _____ in neutral substances.

Answer 15

• red; blue

Question 16

are nitrates soluble?

Answer 16

• yes, all nitrates are soluble in water

Question 17

are sulphates soluble?

Answer 17

• yes, common sulphates are soluble (except barium, calcium and lead (II)) in water

Question 18

are chlorides soluble?

Answer 18

• yes, common chlorides are soluble (except silver and lead (II)) in water

Question 19

are carbonates soluble?

Answer 19

• no, common carbonates are not soluble (except sodium, potassium and ammonium) in water

Question 20

are common hydroxides soluble?

Answer 20

• no, common hydroxides are not soluble (except sodium, potassium, ammonium and calcium (partially)) in water

Question 21

common ________, _________ and __________ compounds are soluble in water

Answer 21

sodium; potassium; ammonium

Question 22

observations when sodium is burnt in oxygen

Answer 22

• intense yellow flame

* white solid produced

Question 23

observations when magnesium is burnt in oxygen

Answer 23

• bright white flame

* white solid produced

Question 24

observations when sulphur is burnt in oxygen

Answer 24

• blue flame

* white fumes

Question 25

observation when carbon is burnt in oxygen

Answer 25

• glowed red

Question 26

word equation and symbol equation for reaction between sodium and oxygen

Answer 26

* sodium + oxygen —> sodium oxide | * 4Na + O₂ —> 2Na₂O

Question 27

what colour does UI turn when added to sodium oxide?

Answer 27

• purple (strong alkali)

Question 28

word equation and symbol equation for reaction between magnesium and oxygen

Answer 28

* magnesium + oxygen —> magnesium oxide | * 2Mg + O₂ —> 2MgO

Question 29

what colour does UI turn when added to magnesium oxide?

Answer 29

• blue (weak alkali)

Question 30

word equation and symbol equation for reaction between sulphur and oxygen

Answer 30

* sulphur + oxygen —> sulphur dioxide | * S + O₂ —> SO₂

Question 31

what colour does UI turn when added to sulphur dioxide?

Answer 31

• red (strong acid)

Question 32

word equation and symbol equation for reaction between carbon and oxygen

Answer 32

* carbon + oxygen —> carbon dioxide | * C + O₂ —> CO₂

Question 33

what colour does UI turn when added to carbon dioxide?

Answer 33

• yellow (weak acid)