Chemistry
Acids and Bases
An indicator tells you if a substance is acidic or basic because the indicator is one colour in an acid and another
in a base.
Indicator
Litmus
Phenopthalein
Methyl Orange
Screened Methyl Orange
Bromothymol Blue

Acid
Red
Colourless
Red
Red
Yellow
Base
Blue
Pink
Yellow
Green
Blue
The pH Scale
The strength of an acid or base is indicated by its pH. The pH tells you the amount of H + ion (acid) or OH- ions
(base) in solution. The pH scale is a number line which runs from 0 to 14.
Therefore, the strongest acid has a pH- 0.
The strongest base has a pH- 14.
And, neutral is pH- 7.
 Acids
An acid is defined as a substance which produces “free hydrogen ions” H+ when dissolved in water.
Example:
HCl(g) ---------w-a-t-e-r-------- > H+(aq) + Cl-(aq)
Some common acids:
-Hydrochloric acid: HCl
-Nitric acid: HNO3
-Sulphuric acid: H2SO4
-Ethanoic acid: CH3COOH
The strength of an acid:
-Strong acids are completely ionized when dissolved in water.
Hence, many H+ ions are available for reaction.
HCl(aq) ----------------- > H+(aq) + Cl-(aq)
(Reaction goes to completion).
List of Strong Acids:
Strong Acids
Symbol
Hydrochloric
Hydrobromic
Hydroiodic
Nitric
Sulfuric
Chloric
Perchloric
HCl
HBr
HI
HNO3
H2SO4
HClO3
HClO4
-Weak acids are partially ionized. Few H+ ions are not available for reaction.
CH3COOH(aq)
CH3COO-(aq) + H+(aq)
(Reaction is reversible).
The Basicity (protocity)- the number of H+ ions liberated per molecule of acid dissolved.
Example:
Monobasic Acids- 1 H+ ion
HCl, HNO3, CH3COOH, etc.
Dibasic Acids- 2 H+ ions
H2SO4
Tribasic Acids- 3 H+ ions
H3PO4
 Some important acid reactions
- Acid + Base ----- > Salt + Water
- Acid + Metal ----- > Salt + Hydrogen
- Acid + Carbonate ------ > Salt + Water + Carbon Dioxide
- Acid + Hydrogencarbonate -------- > Salt + Water + Carbon Dioxide
 Salt formed as product
Salts are substances formed when the hydrogen of an acid is replaced by a metal ion.
When naming a salt, the metal (ion) in the reaction forms the first part of the name, while that of the acid
forms the rest of the name.
Name of Acid
Hydrochloric acid
Sulphuric acid
Nitric acid
Ethanoic acid
Name in SALT Formed
Chloride
Sulphate
Nitrate
Ethanoate
Examples:
1) Zinc + Hydrochloric acid ----- > Zinc chloride + Hydrogen
Zn(s) + 2HCl(aq)
------ > ZnCl2(aq)
+ H2(g)
2) Calcium carbonate + Nitric Acid ------- > Calcium nitrate + Carbon dioxide + Water
CaCO3(s)
+ 2HNO3(aq) ------- > Ca(NO3)2(aq)
+ CO2(g)
+ H 2O
 Bases
Bases are substances which react with H+ ions to produce salts and water only. Bases (OH-) include metal
oxides, hydroxides and ammonia gas.
Some common bases:
-Sodium hydroxide: NaOH
-Calcium hydroxide: Ca(OH)2
-Potassium hydroxide: KOH
-Aqueous ammonia- NH4OH
The strength of a base:
-Strong bases are completely ionized when dissolved in water.
Hence, many OH- ions are available for reaction.
NaOH(aq) ----------------- > Na+(aq) + OH-(aq)
(Reaction goes to completion).
List of Strong Bases:
Strong Bases
Symbol
Lithium Hydroxide
Sodium Hydroxide
Potassium Hydroxide
Calcium Hydroxide
Barium Hydroxide
Rybidium Hydroxide
Caesium Hydroxide
Strontium Hydroxide
LiOH
NaOH
KOH
Ca(OH)2
Ba(OH)2
RbOH
CsOH
Sr(OH)2
-Weak bases are partially ionized. Few OH- ions are not available for reaction.
NH3(g) + H2O(l)

NH+(aq) + 0H-(aq)
(Reaction is reversible).
Some important base reactions
-Acid + Base ------------- > Salt + Water
(Example shown above for acid reaction with base).
-Alkali + Ammonium compound --------------- > Salt + Water + Ammonia
NaOH(aq) + NH4Cl(aq)
------------------ > NaCl(aq) + H2O(l) + NH3(g)
 Determining Neutralisation Point
When an acid or base reacts, the point at which the acid/base is just used up has a pH of 7. This is the
neutralization point of the reaction. Neutralisation point can be determined in 2 ways:
-Thermometrically: by determining the highest temperature of the reaction.
-Titration: several drops of indicator are placed in a known volume of the alkali. The acid is run carefully from a
burette until the exact point when the indicator changes colour. This is the neutralization point of the
reaction.

Acid/ Base Properties of Oxides
Oxides contain oxygen and another element. Oxides show acid/base properties.
Acid Oxides:
The oxides of most non-metals when dissolved in water form acidic solutions.
These oxides are also referred to as acid anhydrides.
SO2(g) + H2O(l) ------------ > H2SO3(aq)
SO3(g) + H2O(l) ------------ > H2SO4(aq)
CO2(g) + H2O(l) ------------ > H2CO3(aq)
Neutral Oxides:
The few non-metals produce oxides that are not acidic or basic are CO, NO and N2O.
Basic Oxides:
The oxides of the most metals are basic. They react with acids to give a salt and water only.
MgO(s) + 2HNO3(aq) ------------- > Mg(NO3)2(aq) + H2O
Soluable basic oxides react with water to produce alkalis such as Na2O, K2O and CaO.
K2O(s) + H2O(l) --------------- > 2KOH(aq)
Amphoteric Oxides:
A few metals react with both acids and bases. The most common ones are PbO, Al 2O3 and ZnO.
PbO(s) + 2HNO3(aq) --------------- > 2KOH(aq)
ZnO(s) + 2NaOH(aq) --------------- > ZnCl2(aq) + H2O(l)