pH scale and indicators
I can explain the pH scale and appropriately use universal indicator, phenolphthalein, methyl orange, and litmus and pH meters to identify different solutions.
pH scale and indicators
I can explain the pH scale and appropriately use universal indicator, phenolphthalein, methyl orange, and litmus and pH meters to identify different solutions.
These resources will be removed by end of Summer Term 2025.
Lesson details
Key learning points
- The pH scale ranges from 0 to 14, indicating how acidic or basic a substance is.
- Universal indicator provides a full range of colours corresponding to different pH levels, and this can be a limitation.
- Phenolphthalein changes from colourless to pink in alkaline conditions.
- Methyl orange shifts from red in acidic conditions to yellow in basic conditions.
- Litmus paper turns red in acidic conditions and blue in basic conditions, the solution will be purple when neutral.
Keywords
PH scale - a scale of acidity or alkalinity, often shown to be between values of 0 and 14
Indicator - a solution or paper which will change a different colour depending on pH of a solution
PH meter - an electric device which measures pH and provides a value after being calibrated with reference samples
Acidity - the concentration of hydrogen ions (H⁺) present in a solution; acids have a pH value less than 7
Alkalinity - the concentration of hydroxide ions (OH⁻) present in a solution; alkalis have a pH value greater than 7
Common misconception
All indicators provide precise pH values and give the same information as pH meters.
Indicators do not provide exact pH values; they only indicate whether a solution is acidic, neutral, or alkaline by changing colour. A pH meter, on the other hand, measures the exact pH value of a solution and is more accurate.
Equipment
spotting tiles, UI solution, phenolphthalein solution, methyl orange solution (fresh), litmus paper (red and blue), pH meter (optional)
Content guidance
- Risk assessment required - chemicals
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Lesson video
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