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Year 9

pH scale and universal indicator solution

I can measure the pH of an acid or alkali using the pH scale.

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New
New
Year 9

pH scale and universal indicator solution

I can measure the pH of an acid or alkali using the pH scale.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Most acids and alkalis are colourless solutions, so indicators can be used to identify them.
  2. pH stands for ‘potential of hydrogen’ and acids contain hydrogen.
  3. The higher the concentration of hydrogen, the lower the pH.
  4. The pH scale goes up and down in factors of ten, so an acid of pH 2 is ten times more acidic than pH 3.
  5. A low pH means acidic, a high pH means alkaline and solutions with a pH of 7 are neutral.

Common misconception

The difference between concentrated and dilute vs strong and weak when referring to acids and alkalis (not covered in this lesson).

For acids and alkalis concentration is the amount of hydrogen dissolved in a certain volume of solution. The higher the concentration, the lower the pH. Strong and weak refer to the ability of an acid to release hydrogen (not covered in lesson).

Keywords

  • PH scale - A scale from 1 to 14 used to measure the acidity or alkalinity of solutions. pH7 is for neutral solutions.

  • Acidic - A solution that has a pH of less than 7.

  • Alkaline - A solution that has a pH of more than 7.

  • Neutral solution - A solution that has a pH of 7.

  • Concentration - The amount of chemical dissolved in a certain volume of solution.

Be aware of pupils with colour vision problems as this lesson can be challenging for them to determine pH's from colour charts, perhaps let them use a pH probe if one is available.
Teacher tip

Equipment

Universal indicator paper or solution, test tubes, test tube racks, plastic pipettes, spotting tiles, indicator charts.

Content guidance

  • 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).

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Starter quiz

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6 Questions

Q1.
Match the keyword to the correct statement
Correct Answer:acid,A solution with a pH of less than 7.

A solution with a pH of less than 7.

Correct Answer:alkali,A soluble base with a pH greater than 7.

A soluble base with a pH greater than 7.

Correct Answer:base,A substance which reacts with an acid to form a salt and water.

A substance which reacts with an acid to form a salt and water.

Q2.
Which of these statements about chemical reactions are true?
Correct answer: New products are made when a chemical reaction occurs.
New reactants are made when a chemical reaction occurs.
Correct answer: The total mass of reactants is the same as the total mass of the products.
No new substances are formed when a chemical reaction occurs.
Q3.
What is the result if blue litmus paper is dipped into lemon juice?
It stays blue.
Correct answer: It turns red.
It turns green.
It turns yellow.
Q4.
What is the result if red litmus paper is dipped into soapy water?
Correct answer: It turns blue.
It stays red.
It turns green.
It turns yellow.
Q5.
True or false? Vinegar can be used to neutralise sodium hydroxide.
Correct answer: true
false
Q6.
Which containers of liquid may require a corrosive hazard label?
water
milk
Correct answer: sulfuric acid
Correct answer: sodium hydroxide (an alkali)

Exit quiz

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6 Questions

Q1.
Match the keyword to the correct statement.
Correct Answer:pH scale,Measures the acidity or alkalinity of solutions.

Measures the acidity or alkalinity of solutions.

Correct Answer:neutral,A solution that has a pH of 7.

A solution that has a pH of 7.

Correct Answer:alkali,A solution with a pH of more than 7.

A solution with a pH of more than 7.

Correct Answer:acid,A solution with a pH of less than 7.

A solution with a pH of less than 7.

Q2.
A bee sting is acidic. What colour would universal indicator turn?
blue
green
Correct answer: red
purple
Q3.
What does pH stand for?
Correct answer: potential of hydrogen
potential of hydroxide
potential of helium
potential of harm
Q4.
Four solutions were tested with universal indicator. Rank the results in terms of acidity. Place the most acidic solution first.
1 - red
2 - orange
3 - yellow
4 - blue
Q5.
Select the correct statements about concentration of hydrogen and pH.
Correct answer: The higher the concentration of hydrogen, the lower the pH.
The higher the concentration of hydrogen, the higher the pH.
Correct answer: The lower the concentration of hydrogen, the higher the pH.
The lower the concentration of hydrogen, the lower the pH.
Q6.
Solution A has a pH of 8 and solution B has a pH which is 1000 times more alkaline. What is the pH of solution B?
Correct answer: 11
10
9
7