Indicators and pH

• Science
• Lower Secondary (Key Stage 3)

Most often scientist will use universal indicator as a first choice. Why do you think it is more popular?

What did your results tell you about the chemicals we tested yesterday?

Acid

Alkali

Coca Cola

Vinegar

Hydrochloric acid

Sodium hydroxide

Shower gel

Name a weak acid

Name a strong acid

Name a weak alkali

Name a strong alkali

What is this substance?

1. Strong acid
2. Weak acid
3. Strong alkali
4. Weak alkali

What is this substance?

1. Strong acid
2. Weak acid
3. Strong alkali
4. Weak alkali

What is this substance?

1. Strong acid
2. Weak acid
3. Strong alkali
4. Weak alkali

1. Which one(s) are acidic?
2. Which one(s) are neutral?
3. Which one(s) are alkaline?
4. What is the difference between A and C?

Match the keywords to the diagram.

Acid

Alkali

Neutral

Weak

Weak

Strong

Strong

Why might it be difficult to test a leaf with universal indicator?

What is the pH of:
a. An acid?
b. An alkali?
c. A neutral substance?

pH 2

1. Strong acid
2. Weak acid
3. Neutral
4. Weak alkali

pH 10

1. Strong acid
2. Weak acid
3. Neutral
4. Weak alkali

pH 7

1. Strong acid
2. Weak acid
3. Neutral
4. Weak alkali

pH 6

1. Strong acid
2. Weak acid
3. Neutral
4. Weak alkali

Solution            Colour         pH

pH 14

pH 4

pH 1

pH 10

pH 7

Purple

Red

Green

orange

Blue

Sort the keywords into the correct box.

Acid

Alkali

Sour

Bitter

pH 10

pH 1

Red - Orange

pH 5

pH above 7

pH 8

Blue- Purple

pH Below 7

A pupil adds water to an alkaline solution. What will happen to the pH?

You have two unlabelled beakers. One contains a strong acid and one contains a weak acid. How could you identify which is which?

Hydrangeas are biological indicators. What do you think that might mean?

Look at your results table. Use the diagram to estimate the pH of each substance.