Starter quiz
- What is the pH range of acids?
- 0 to 7 ✓
- 0 to 14
- 7 to 14
- 4 to 10
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- Which of the following is common laboratory equipment used to measure pH?
- burette
- volumetric pipette
- pH meter ✓
- beaker
-
- What colour does litmus paper turn in an acidic solution?
- blue
- green
- red ✓
- yellow
- purple
-
- What does a pH value of 7 indicate?
- acidic solution
- basic solution
- neutral solution ✓
- strong acid
-
- Which ion's concentration is high in acidic solutions?
- OH⁻ (hydroxide)
- Na⁺ (sodium)
- H⁺ (hydrogen) ✓
- Cl⁻ (chloride)
-
- What should you always wear to protect your eyes in a laboratory?
- gloves
- lab coat
- mask
- safety goggles ✓
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Exit quiz
- How does the pH scale indicate whether a substance is acidic or basic?
- By showing the colour change in universal indicator.
- By the number ranging from 0 to 14. ✓
- By measuring the temperature of the solution.
- By indicating the volume of the solution.
-
- What colour does methyl orange turn in acidic conditions?
- red ✓
- yellow
- green
- blue
-
- What is the pH of a neutral solution?
- '7' ✓
- Which indicator changes from colourless to pink in alkaline conditions?
- litmus paper
- methyl orange
- phenolphthalein ✓
- bromothymol blue
-
- How does litmus paper indicate a neutral solution?
- turns blue
- turns red
- remains unchanged ✓
- turns green
-
- What is a limitation of using universal indicator?
- It only shows one colour for all pH levels.
- It provides a full range of colours but might not pinpoint the exact pH. ✓
- It cannot be used with strong acids or bases.
- It changes colour too slowly.
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Worksheet
Presentation
Video
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.
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.
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