THE pH SCALE - UNIVERSAL INDICATOR AND LITMUS

1. THE pH SCALE

2. IMPORTANT POINTS
 The pH scale measures how acidic or alkaline a
substance is.
 Universal indicator changes to different colours in
different indicators.
 A pH below 7 is acidic
 A pH above 7 is alkaline
 A pH that is 7 is nuteral
 Litmus is a paper which tells us whether a substance
is an acid or base.

3. WHAT IS A Ph SCALE?
 The pH scale measures whether there is more
hydronium or hydroxide in a solution. In other
words, it tells us how basic or acidic the solution is. A
lower pH means something is more acidic, also
known as a stronger acid. A higher pH means it is
more alkaline or a stronger base.
 Chemistry classes will often use a litmus test to
identify acids from bases. A blue litmus paper turns
red in acids while a red litmus paper turns blue in
basic solutions. Other pH indicator papers are
available that will actually identify the rough pH of
some acid or base, also using color-change chemicals.

4. A COLOUR CHART FOR
UNIVERSAL INDICATOR
SHOWING THE pH SCALE

5. UNIVERSAL INDICATOR
 A universal indicator is a pH indicator
made of a solution of several compounds
that exhibits several smooth colour
changes over a wide range pH values to
indicate the acidity or alkalinity of
solutions.
 the universal indicator shows how acidic
of alkaline a substance is. This indicator
can change to many different colours.

6. TYPES OF COLOURS AND
IT’S SUBSTANCE:
TYPE OF SUBSTANCE COLOUR OF UNIVERSAL
INDICATOR.
STRONGLE ACIDIC RED
WEAKLY ACIDIC YELLOW
NUTERAL GREEN
WEAKLY ALKALINE BLUE
STRONGLY ALKALINE PURPLE

7. LITMUS:
 LITMUS IS A VERY COMMON INDICATOR
IT IS A DYE. LITMUS TURNS BLUE IN
ALKALIS. LITMUS TURNS RED IN ACIDS.
LITMUS TURNS PURPLE IN A NEAUTRAL
SUBSTANCE. THIS IS A SUBSTANCE THAT
IS NEITHER ACID NOR ALKALI.
LITMUS TURNS PURPLE IN WATER. THIS
MEANS WATER IS NEITHER AN ACID OR
ALKALIS.

8. LITMUS – SUBSTANCE,
COLOUR AND SUBSTANCE
TYPE.
Substance Litmus colour Types ofsubstances
Hydrochloric acid Red Acid
Sodium hydroxide Blue Alkali
Water Purple Neutral
Lemon juice Red Acid
Calcium hydroxide blue alkali

9. IMPORTANT POINTS:
 An indicator changes colour in an acid or
alkali.
 Some plant materials make good
indicators.
 Substances that are neither acid or alkalis
are called neuteral.