CI 8.1 Acids and Bases
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Transcript of CI 8.1 Acids and Bases
CI 8.1 Acids and Bases
Acids
Turn litmus red
Neutralised by bases
pH < 7
Liberate CO2 from carbonates
BrØnsted-Lowry Theory
An acid is an H+ donor
A base is an H+ acceptor
H+Cl- + NH3 Cl- + NH4+
The oxonium ion
An acid reacts with water to form oxonium ions
HCl + H2O H3O+ + Cl-
Water is acting as a base
The oxonium ion
H
O
H
H+x
xWhat type of bond is this?
Is there a difference between an alkali and a base?
A base is a substance which accepts H+ ions
Alkali = a base which forms OH-
ions in water
How are hydroxide ions (OH-) made?
NaOH Na+ + OH-
CO32- + H2O HCO3
- + OH-
NH3 + H2O NH4+ + OH-
Acid – base pairs
CH3COOH CH3COO- + H+
CH3COO- + H+ CH3COOH
The ethanoate ion can behave as a base; it is the conjugate base of ethanoic acid.
HA H+ + A-
Conjugate acid
Conjugate base
Every acid has a conjugate base Every base has a conjugate acid
Amphoteric substances
Water can act as either an acid or a base
With a strong acid it acts as a base
With a strong base it acts as an acid
A substance which behaves in this way is said to be amphoteric
Water in the presence of a strong acid:H3O+ H+ + H2O
Water in the presence of a strong base:H2O H+ + OH-
Water as an amphoteric substance
Strength of acids and bases
A strong acid is a powerful H+ donor; it is fully dissociated
A weak acid is a moderate or weak H+ donor; it is weakly dissociated
A strong acid has a weak conjugate base and vice versa
Indicators
Coloured organic substances Weak acids Conjugate acid and conjugate base
forms are different colours e.g. litmus:
HIn H+ + In-
red blueWhich is the acid form?
Addition of acid
In- + H3O+ HIn + H2O
The blue litmus turns red
What is the equation for addition of alkali?