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.
- Year 10
- AQA
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.
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
Lesson video
Loading...
