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2
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Strength
- how many of its molecules release H+/ OH- into a solution
- acids and bases that completely dissociate are strong
- influenced by the stability of other chemicals

Strong acid: HBr --> H+ + Br

ii
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g
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5 & 8
Between 3 & 5
Between 8 & 10
Between 3 & 4
...
5-7
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5-7
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5-3
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2 Acid Reactions
Acids and Metals


Acid + metal --> a salt + hydrogen gas
- Salt – any compound formed by a metal replacing Hydrogen atoms in an acid

Hydrochloric acid + magnesium --> magnesium chloride + hydrogen gas
2 HCl (aq) + Mg (s) --> MgCl2 (aq) + H2 (g)

Neutralisation


Acid + base --> salt + water

Nitric acid + potassium oxide --> potassium nitrate + water
2 HNO3 + K2O --> 2KNO3 + H2O


Titration indicates neutralisation – if moles of acid = moles of base
3




Products formed from equal weights of acid and base
Bases include metal oxides

Acids and Carbonates


Acid + carbonate --> salt + water + carbon dioxide

Hydrochloric acid + calcium carbonate --> calcium chloride + water + carbon dioxide
2 HCl + CaCO3 --> CaCl2 + H2O + CO2
Ethanoic acid + sodium hydrogen carbonate --> sodium acetate + water + carbon dioxide
CH3COOH + NaHCO3 --> NaCH3COO + H2O + CO2

Acid Rain
Water + carbon dioxide --> carbonic acid
H2O + CO2 --> H2CO3


Pollution:
- Cause rainwater to become more acidic
- Combustion of fossil fuels release SO2 and nitrogen oxides (NO2)
- Results in more carbonic acid in rain – formed by sulphur dioxide & nitrogen dioxide with
water vapour

Sulphur dioxide + water vapour --> sulphurous acid
SO2 + H2O --> H2SO3
Sulphur dioxide + water vapour + oxygen gas --> sulphuric acid
2 SO2 + 2 H2O + O2 --> 2 H2SO4
Nitrogen dioxide + water --> nitrous acid + nitric acid
2 NO2 + H2O --> HNO2 + HNO3



Rainwater dissolves acids and returns them to Earth as acid rain (or dew, fog, sleet, hail or snow)
pH of acid rain as low as 3
...
5 (approx
...
4 and 7
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3 Rates of Chemical Reactions
Rate of Reaction





How fast a chemical reaction proceeds
Total amount of reactant used or product made over time
Fast reactions: explosions and combustion reactions (e
...
vinegar + bicarbonate soda; burning gas in
Bunsen burner)
Slow reactions: rusting, ripening and fermentation of wine

Factors Determining a Reaction
1
...
Orientation
- Allow bonds to break and new bonds to form
- Incorrect orientation results in unsymmetrical particles bouncing off each other
3
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Temperature
- Increases the speed of particle movement
- Give particles more energy
2
...
Agitation
- Ensures the reactants are kept in contact
- Removes build-up products around the reactants
4
...
Catalysts
- Chemicals that speed up reactions without using up themselves
i
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Make it easier for reactant molecules to collide and reactant to form products (reactants
attached to the surface of a catalyst lead to more collisions)
6
...

Hydrogen gas – pop test
ii
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Change in shape or form (break, bend, stretch, crush, twist or compress)
ii
...

Changes of state
iv
...

Permanent colour change
ii
...

Formation of precipitate
iv

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