CHAP 8 ACIDS & BASES

Question 1

state the
-definition
- PHYSICAL properties of ACIDS [2] :
- CHEMICAL properties of ACID

Answer 1

-a substance that dissolves in water to produce hydrogen ions H+

1) have a sour taste
2) turns blue litmus paper red
3) gives solution with pH values <7

• HOWEVER, as hydrogen ions are responsible for properties of acid -> acid that is not dissolved in water does not show such properties

CHEM PROP.
1) dilute acid reacts with metals that lie above hydrogen in the reactivity series -> produces salt + hydrogen gas
* gold, silver, copper DO NOT react with dilute acids
2) dilute acid reacts with carbonates to produce SALT + CO2 + H2O
3) acids reacts with bases to form SALT & WATER
->bases could be metal oxides or alkali

• lead DOES NOT react with HCI & H2SO4
  -> due to formation of a layer of insoluble salt around the metal -> prevents contact between the acid and metal-> causing reaction to end prematurely

Question 2

state the commonly used acid + the chemical formula [3]

Answer 2

hydrochloric acid HCI
sulphuric acid H2SO4
nitric acid HNO3

Question 3

state the definition of BASE/ALKALI
- PHYSICAL properties [3]
- CHEMICAL properties [2]

Answer 3

• a metal oxide or hydroxide that reacts with acids to produce salt & water
• alkali dissolves in water to produce hydroxide ions OH-

PHYSICAL PROPERTY
-have bitter taste
-turns red litmus paper blue
- gives solution with pH values >7

CHEMICAL PROPERTIES
1) undergo neutralisation with acids to produce SALT & WATER only
neutralisation -> H+ (aq) + OH- (aq) -> H2O (l)
2) alkali + ammonium salts -> SALT + WATER + NH3 (ammonia gas)

Question 4

pH scale

Answer 4

• a measure of acidity / basicity of substance that are dissolved in water
  ( based on the relative concentrations of H+ & OH- ions present )
  1) ranges from 0-14
  2) acidity - <7
• acid has higher concentration of H+ ions compared to OH- ions
• acid with higher concentration of H+ ions would have lower pH compared to acid with lower concentration of H+ ions
  3) basicity- >7
• base with higher concentration of OH- ions has higher pH than a base with lower concentration of OH- ions
  4) neutral - 7