Acids and Alkalis Worksheet - KS3 - Intermediate

Acids and Alkalis worksheet for KS3 (Key Stage 3 / Year 7-9 (Ages 11-14)). Intermediate level science practice, aligned to the UK National Curriculum. Print-ready with answer key included.

Science•Key Stage 3 / Year 7-9 (Ages 11-14)•Acids and Alkalisintermediate

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Acids and Alkalis: pH, Indicators and Neutralisation

Key Stage 3 / Years 7–9 (ages 11–14) · Intermediate

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Instructions: Work through the activities in order, using the information given in each question. Show calculations and explain scientific ideas clearly in the answer spaces. Use the pH scale and indicator colour key provided rather than relying on guesswork.

Read the pH Scale

Use the pH values shown in the scale to classify each substance as acidic, neutral or alkaline. Remember: pH below 7 is acidic, pH 7 is neutral, and pH above 7 is alkaline. Give the classification, not just the pH value.

pH scale: 0–6 = acidic | 7 = neutral | 8–14 = alkaline

1. Lemon juice, pH 2: classify it.

2. Pure water, pH 7: classify it.

3. Soap solution, pH 10: classify it.

4. A liquid has pH 5. Is it acidic, neutral or alkaline?

5. Which is more alkaline: pH 8 or pH 12?

Indicators and Colour Changes

Use the colour key to work out what each indicator result tells you. Universal indicator shows a range of colours across the pH scale; litmus gives a simpler acid-or-alkali test. State the conclusion requested for each result.

Universal indicator key: red/orange = acidic; green = neutral; blue/purple = alkaline.

Litmus key: blue litmus turns red in acid; red litmus turns blue in alkali.

1. Universal indicator turns orange. Is the sample acidic, neutral or alkaline?

2. Universal indicator turns green. What is the approximate pH?

3. Universal indicator turns purple. Is the sample acidic or alkaline?

4. Blue litmus paper turns red. Is the sample acidic or alkaline?

5. Red litmus paper stays red. Can this result alone show that the sample is an alkali? Answer yes or no.

Everyday Acids and Alkalis

Classify each familiar substance using the information provided. Some household products can be harmful, so this activity is about their properties only: never taste or mix household chemicals. Write acidic, neutral or alkaline for each.

1. Vinegar, pH 3:

2. Baking soda solution, pH 8:

3. Milk, pH 6:

4. Oven cleaner, pH 13:

5. Pure water, pH 7:

Neutralisation in Reactions

Use the word bank to complete each statement about neutralisation. A neutralisation reaction happens when an acid reacts with an alkali. Check that each chosen word makes the scientific statement accurate.

Word bank: acid, alkali, neutral, salt, water

1. In neutralisation, an __________ reacts with an __________.

2. The general products are a __________ and __________.

3. If enough alkali is added to an acid, the mixture can become __________.

4. Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and __________.

Use the Results

Study the table, then answer the questions using its data. For the calculation, find how far the pH has changed by subtracting the starting pH from the final pH. Remember that a rise in pH means the mixture has become less acidic or more alkaline.

Stage	Indicator colour	pH
Before adding alkali	red	2
After a small addition	orange	4
After more alkali	green	7
After excess alkali	blue	9

1. What was the pH before alkali was added?

2. At which stage was the mixture neutral?

3. By how many pH units did the pH rise from the start to the neutral stage?

4. Was the final mixture acidic or alkaline?

Explain Neutralisation

Write a concise scientific explanation using the pH scale and the reaction information in the prompt. Include what happens to the pH as an acid is neutralised and identify the products. Use the key terms from earlier activities where helpful.

Explain what happens when an alkali is added gradually to an acid until the mixture is neutral. In your answer, state how the pH changes and name the two general products of neutralisation. [4 marks]

Answer Key

Activity 1: Acidic ; Neutral ; Alkaline ; Acidic ; pH 12

Activity 2: Acidic ; pH 7 ; Alkaline ; Acidic ; No

Activity 3: Acidic ; Alkaline ; Acidic ; Alkaline ; Neutral

Activity 4: acid ; alkali ; salt ; water ; neutral ; water

Activity 5: 2 ; After more alkali ; 5 pH units ; Alkaline

Activity 6: The pH rises from the acidic range towards 7 as alkali is added. At neutralisation, the acid and alkali have reacted; the general products are a salt and water.