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pH Scale

In this worksheet, students will receive an introduction to acids and alkalis and the use of the pH scale to identify a substance as being acidic, alkaline or neutral and indicating the relative strength of the acid or alkali.

'pH Scale' worksheet

Key stage:  KS 3

Curriculum topic:  Chemistry: Chemical Reactions

Curriculum subtopic:  pH Scale

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

Acids have a reputation for being nasty chemicals that burn through floors and metal structures with great ease. But did you realise the vinegar is an acid? This worksheet tackles some of the myths associated with acids and their chemical opposites - alkalis. Many of the products you find at home are acidic or alkaline.

 

Having vinegar on your chips is not dangerous, but drinking a lab acid like hydrochloric acid could be fatal.  This is because hydrochloric acid is much stronger acid than vinegar

.
The strength of an acid or alkali can be measured using the pH scale.

 

pH Scale

 

The pH scale is a measure of how strong or weak an acid or alkali is. It is a continuous scale from below 0 to above 14. The colour chart below shows the colour that universal indicator turns when it’s mixed with solutions of different pHs:

 

pH scale

 

Neutral solutions such as water have a pH of 7.

 

Acids have a pH of less than 7. The lower the pH number of an acid the stronger the acid is.  So an acid like hydrochloric acid with a pH of 1 is a lot stronger than vinegar with a pH of 3.

 

Alkalis have a pH of greater than 7. The higher the pH number of an alkali the stronger it is. So an alkali like sodium hydroxide with a pH of 14 is a lot stronger than baking soda with a pH of 9. 

Using the table below, decide wether the substances are acidic, alkaline or neutral. 

 AcidicAlkalineNeutral
Vinegar
Baking soda
Lemon juice
Bleach
Water

Match up the pH numbers to the substances listed on the left.

Column A

Column B

Hydrochloric acid
pH 2
Vinegar
pH 1
Lemon Juice
pH 3

Match up the pH numbers to the substances on the left.

Column A

Column B

Sodium hydroxide
pH 14
Baking soda
pH 9
Ammonia
pH 11

Write this sentence out again in the answer box below, filling in the gap with the correct word. Don't forget the full stop!

 

Hydrochloric acid is a much _____________ acid than vinegar.

Write this sentence out again in the answer box below, filling in the gap with the correct word. Don't forget the full stop!

 

Universal Indicator turns _____ with an alkali of pH 14.

Which of the following substances would have the lowest pH number?

lemon juice

vinegar

hydrochloric acid

lemonade

Which of the following substances would have the highest pH number?

milk

sodium hydroxide

bicarbonate of soda

toothpaste

Limescale, which can be formed in kettles, is an alkali. Which of the following substances can be added to a kettle to remove the limescale?

lemon juice

milk

toothpaste

What name is given to the chemical reaction between an acid and an alkali?

neutralisation

precipitation

condensation

An unknown clear liquid is tested with pH paper. The pH paper turns a green colour.

Which of the following substances may be the unknown liquid?

Sulfuric acid

Potassium hydroxide

water

  • Question 1

Using the table below, decide wether the substances are acidic, alkaline or neutral. 

CORRECT ANSWER
 AcidicAlkalineNeutral
Vinegar
Baking soda
Lemon juice
Bleach
Water
EDDIE SAYS
The pH scale is commonly used in all walks of life from gardening to pet care. As a result, pH indicators can be purchased from DIY and pet stores. You could always ask your parents if they can buy one, and then you can test the pH of substances around your home!
  • Question 2

Match up the pH numbers to the substances listed on the left.

CORRECT ANSWER

Column A

Column B

Hydrochloric acid
pH 1
Vinegar
pH 3
Lemon Juice
pH 2
EDDIE SAYS
All acids have pH lower than 7. The lower the pH number the more acidic the substance is.
  • Question 3

Match up the pH numbers to the substances on the left.

CORRECT ANSWER

Column A

Column B

Sodium hydroxide
pH 14
Baking soda
pH 9
Ammonia
pH 11
EDDIE SAYS
All alkalis have a pH greater than 7. The higher the pH the more alkaline a substance is.
  • Question 4

Write this sentence out again in the answer box below, filling in the gap with the correct word. Don't forget the full stop!

 

Hydrochloric acid is a much _____________ acid than vinegar.

CORRECT ANSWER
Hydrochloric acid is a much stronger acid than vinegar.
EDDIE SAYS
The lower the pH of an acid the more acidic it is. Hydrochloric acid has a pH of 1 or less whereas vinegar has a pH of three. This means that vinegar is at least 100 times weaker than hydrochloric acid.
  • Question 5

Write this sentence out again in the answer box below, filling in the gap with the correct word. Don't forget the full stop!

 

Universal Indicator turns _____ with an alkali of pH 14.

CORRECT ANSWER
Universal Indicator turns purple with an alkali of pH 14.
EDDIE SAYS
The colour of all Universal Indicators will vary slightly, so always check the colour chart that will accompany any Universal Indicators that have been purchased. However, most strong alkalis will turn indicators a purpley colour.
  • Question 6

Which of the following substances would have the lowest pH number?

CORRECT ANSWER
hydrochloric acid
EDDIE SAYS
The more acidic the substance is, the lower pH number it has.
  • Question 7

Which of the following substances would have the highest pH number?

CORRECT ANSWER
sodium hydroxide
EDDIE SAYS
The more alkaline a substance is, the higher pH number it has.
  • Question 8

Limescale, which can be formed in kettles, is an alkali. Which of the following substances can be added to a kettle to remove the limescale?

CORRECT ANSWER
lemon juice
EDDIE SAYS
If you have limescale in your kettle at home, try adding some lemon juice or vinegar to get it nice and shiny again. Just remember to wash it out before you use it again or your tea may taste a bit funny!
  • Question 9

What name is given to the chemical reaction between an acid and an alkali?

CORRECT ANSWER
neutralisation
EDDIE SAYS
Neutralisation reactions are reactions between acids and alkalis. Depending upon the strength and the volume of each, you may end up with a neutral solution (of a metal salt plus water).
  • Question 10

An unknown clear liquid is tested with pH paper. The pH paper turns a green colour.

Which of the following substances may be the unknown liquid?

CORRECT ANSWER
water
EDDIE SAYS
Usually, pH paper turns green with a neutral substance, with a pH of 7.
---- OR ----

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