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CI 8.1Acids and Bases
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Acids
Turn litmus red
Neutralised by bases
pH < 7
Liberate CO2 from carbonates
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Brnsted-Lowry Theory
An acid is an H+ donor
Abase is an H+ acceptor
H+Cl- + NH3 p Cl- + NH4
+
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The oxonium ion
An acid reacts with water to formoxonium ions
HCl + H2O p H3O+ + Cl-
Water is acting as a base
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The oxonium ion
H
O
H
H+x
xWhat type ofbond is this?
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Is there a difference between an alkali
and a base?
A base is a
substancewhich acceptsH+ ions
Alkali = abase whichforms OH-
ions in water
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How are hydroxide ions (OH-) made?
NaOH Na+ + OH-
CO32- + H2O HCO3- + OH-
NH3 + H2O NH4+ + OH-
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Acid base pairs
CH3COOH CH3COO- + H+
CH3COO- + H+ CH3COOH
The ethanoate ion can behave as abase; it is the conjugate base ofethanoic acid.
HA H+ + A-
Conjugateacid
Conjugatebase
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Every acid has a conjugate base
Every base has a conjugate acid
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Amphoteric substances
Water can act as either an acid or abase
With a strong acid it acts as a base
With a strong base it acts as an acid
A substance which behaves in thisway is said to be amphoteric
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Water in the presence of a strongacid:
H3O+
H+
+ H2O
Water in the presence of a strongbase:
H2O H+ + OH-
Water as an amphoteric substance
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Indicators
Coloured organic substances
Weak acids
Conjugate acid and conjugate baseforms are different colours
e.g. litmus:HIn H+ + In-
red blueWhich is theacid form?
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Addition of acid
In- + H3O+ HIn + H2O
The blue litmus turns red
What is the
equation foraddition ofalkali?