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Primary Science · Year 5Chapter 7 · Reversible and irreversible changes
Year 5 Science · Reversible and irreversible changes · Lesson 7.4

Year 5 Science: Acid and bicarbonate of soda

Part of the Year 5 Science reversible and irreversible changes chapter. Chapter overview · whole chapter on one page

7.4

Acid and bicarbonate of soda

Year 5
M6: explain the action of acid on bicarbonate of soda, which forms new materials and a gas, and is not usually reversible
Story. Priya pours vinegar onto a spoonful of bicarbonate of soda in a cup. It fizzes and bubbles up. “Where is all that gas coming from?” she asks. Her teacher says: “The vinegar is an acid. Acids react with bicarbonate of soda and make new materials, including a gas.”

Vinegar is an acid. When an acid is mixed with bicarbonate of soda, the two materials react together. The reaction makes new materials, including a gas called carbon dioxide. The bubbles and the fizzing are the gas escaping.

This is an irreversible change. The bicarbonate of soda and the vinegar cannot be recovered from the new materials.

gas risesvinegar and bicarbonate of soda: new materials and a gas
A cup in which vinegar and bicarbonate of soda fizz, with bubbles of gas rising.

In a fair test, three equal amounts of bicarbonate of soda were added to vinegar, and the bubbles were counted in 30 seconds.

TrialBubbles counted in 30 seconds
Trial 114
Trial 216
Trial 315

Key ideas

  • An acid reacts with bicarbonate of soda to make new materials.
  • The reaction makes a gas, carbon dioxide, which makes the bubbles and the fizzing.
  • This change is irreversible, because new materials are made.
  • Evidence of a new material includes a gas, a new colour, or a new smell.
Worked example 7.4.1
What does the vinegar do when it is mixed with bicarbonate of soda? Write the word: acid, or gas.

Method. Think about what kind of material vinegar is.

  1. Think about vinegar. Vinegar is an acid, and it reacts with bicarbonate of soda.
    acid
  2. Choose the word. So the word is acid, which describes the vinegar.
    acid
  3. Write the answer.
    acid

Check. Vinegar is an acid. ✓

Worked example 7.4.2
In the fizz test, how many bubbles were counted in trial 2? Write the number.

Method. Read the table.

  1. Read the row for trial 2. The count for trial 2 is 16 bubbles.
    trial 2
  2. Write the number. So there were 16 bubbles in trial 2.
    16
  3. Write the answer.
    16

Check. Trial 2 was the largest count. ✓

Worked example 7.4.3
Is the fizzing reaction between vinegar and bicarbonate of soda reversible? Write yes or no.

Method. Think about the new materials.

  1. Think about the new materials. The reaction makes new materials, including a gas.
    new materials
  2. Decide. So the change cannot easily be undone, and the answer is no.
    no
  3. Write the answer.
    no

Check. New materials are made, so the change is irreversible. ✓

Watch out

Watch out: the bubbles are a gas. They are not the bicarbonate of soda coming back out of the cup, and the change cannot be undone.

Try it (with your teacher). With your teacher, put a spoonful of bicarbonate of soda into a clean cup. Add a small amount of vinegar, and watch the fizz. Count the bubbles for 30 seconds. Repeat the test two more times, using the same amounts each time, and find the mean. Do not taste anything, and wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “What is the gas? Could the vinegar and bicarbonate of soda be recovered from the fizzing mixture?” Keep the amounts small and the test fair.

Exercise 7D  Acid and bicarbonate of soda

1
FIs vinegar an acid? Write yes or no.
2
FWhat gas is made when an acid reacts with bicarbonate of soda? Write the words.
3
FWhat do the bubbles and the fizzing show? Write one word.
4
FLook at the fizz test table in section 7.4. How many bubbles were counted in trial 1? Write the number.
TrialBubbles counted in 30 seconds
Trial 114
Trial 216
Trial 315
5
FLook at the fizz test table in section 7.4. Work out the mean number of bubbles. Write the number.
TrialBubbles counted in 30 seconds
Trial 114
Trial 216
Trial 315
6
PSLook at the fizz test table in section 7.4. Which trial had the most bubbles? Write the trial name.
TrialBubbles counted in 30 seconds
Trial 114
Trial 216
Trial 315
7
PSLook at the fizz test table in section 7.4. How many more bubbles were there in trial 2 than in trial 1? Write the number.
TrialBubbles counted in 30 seconds
Trial 114
Trial 216
Trial 315
8
PSIs the change between vinegar and bicarbonate of soda reversible? Write yes or no.
9
PSWorking scientifically. Compare the evidence. Name one piece of evidence that a new material has formed in the fizz test. Write one word.
10
RExplain why the fizzing mixture cannot easily be turned back into vinegar and bicarbonate of soda. Write one sentence.
11
RExplain why the bubbles in the fizz test are evidence that a new material has been made. Write one sentence.

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