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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?