SLIDES

1. MOFPPB3
MICRO
LESSON
22 AUGUST
2018
BY SN MHLONGO

2. ACIDS & BASES
Many of the substances that we use in our everyday life can be classified
as an acids and bases for example Handy Andy, soaps, Milk of Magnesia
are bases . Citrus fruit, lemon , vinegar can be classified as acids.
In Grade 10 you learnt about the properties of acids & bases . Today we
will look into two Acid & Base Theories as well as the acid-base pairs.

3. When we talk about acids and bases we usually
look into reactions in aqueous solution
In the 19th century a Swedish chemist Arrhenius formulated a definition for an
acid and a base. He said that
An acid – is a substance that ionises in water to produce hydrogen ions
A base- is a substance that ionises in water to produce hydroxide ions
But these definitions are limited because they only apply to acids and bases in
aqueous solution . For example

4. Also in 1923 two chemist Bronsted
& Lowry proposed new definitions .
– Bronsted-Lowry came up with the following definitions of an acid and
a base
– They defined acid as a proton donor
– Base as a proton acceptor
– Their definitions is not limited , it does not require acids and bases to
be in aqueous solution.
– for examples

5. Acid-base pairs
– A conjugate pairs consist of two substance that are related to each
other by the transfer of a proton .
– An acid form its conjugate base when it has donated the proton
E.g.
- A base form its conjugate acid when it has accepted the proton
- E.g.

6. Conjugate pairs
– Conjugate acid – is any base to which a proton has been added
– Conjugate base – is any acid to which a proton has been removed

7. Let us summarise what we have
learnt:
According to Arrhenius
A base is defined as the substance that ionises in water to form hydroxide
ions .
An acid is defined as the substance that ionises in water to from hydrogen
ions.
NB: The theory only apply in acids and bases in aqueous solution
According to Bronsted-Lowry
A base is defined as the proton acceptor
An acid is defined as the proton acceptor
There is no limitation in this theory; it can apply in aqueous solution or not
in aqueous solution.

8. – Conjugate acid – is any base to which a proton has been added
– Conjugate base – is any acid to which a proton has been removed