pH Scale
How do we measure the strength of
acids and bases?
• pH: stands for the strength or concentration of hydrogen
ions (H1+) in a solution.
pH Scale
• pH 7 is neutral. (Water)
• pH 1 is a very acidic.
• pH 13 is a very basic.
Weakly
Acidic
Very Acidic
Weakly
Basic
Neutral
• pH 4 is 10 times stronger than pH 5
• pH 3 is 100 times stronger than pH 5
Very Basic
Stomach
Acid
Ant Bites
Detergents
Blood
Weakly
Acidic
Weakly
Basic
Neutral
Very Acidic
Very Basic
Acid Rain
+
+
H
H
+
H H+
H+ + +
H H
+
H+ H
H+
H+
H+
Drain
Cleaner
OH–
OH–
OH–
OH– OH–
OH–
–
OH
–
OH
–
OH
–
OH
–
OH
–
OH
• Many solutions of acids or bases are clear and
colourless
• We use indicators to distinguish them from
water, and tell whether a substance is acidic,
basic or neutral
• There are many, many indicators, and each one
has a different colour in acidic solutions
versus basic solutions
Some Common indicators are:
1) Phenolphthalein drops (acid/neutral is clear, base is pink)
Some Common indicators are:
2) Litmus paper – red litmus turns blue in base
– Blue litmus turns red in acid
Some Common indicators are:
3) Universal pH paper –
range of colours
Some Common indicators are:
4) Cabbage Juice –
range of colours
Some Common indicators are:
5) pH meter – tells you exact pH
Thymol blue Activity
Instructions
1) Put on your goggles and grab a test tube holder
2) Get 3 test tubes, label HCl & NaOH & mixture
3) Get 2 pipettes, label HCl & NaOH
4) Get ½ a test tube of HCl and NaOH into appropriate
test tubes. Add 2cm of HCl to mixture test tube.
5) Add 3 drops of thymol blue to the mixture test tube
6) Use only the appropriate test tube pipettes to add
acid or base to get all the colours of the scale.
*When you’ve achieved the transition colours, show
Mrs. Innes*
The Importance of pH
1. The pH of environment
effects plants and animals.
ex. hydrangea flowers, frog
or Fish survival
• Netural soils =
white or pale petals
• Acidic soils =
blue petals
• Basic soils =
purple or pink petals.
2. The pH of your body affects your health. If
you are too acidic, yeast and bad bacteria can
grow.
• Normal blood has a pH of 7.4, if pH falls below
6.8 or above 7.8 it is considered fatal.
3. Cosmetic/hair products with different pH’s
have different effects. Acidic ones make hair
shiny and flexible. Basic ones make hair soft
and straight.
Cabbage Lab