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Chemical Changes Investigation

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Chemical Changes Investigation

A class is testing whether mixing vinegar and bicarbonate of soda causes a chemical change. Read the investigation notes and use the evidence to explain your conclusions. Do not taste any materials. Wear safety glasses, work over a tray and wash your hands afterwards.

Plan and predict

Procedure: Measure 30 mL of vinegar into a beaker. Add one level teaspoon of bicarbonate of soda and observe from a safe distance. Record what you notice during the first minute. The beaker is open; never seal a reacting mixture.

1.Before the materials are mixed, write a testable prediction about what you expect to observe. Include what you think will happen when the two substances meet.

2.Which measurement should stay the same if you repeat the test fairly? Choose the best answer.

The volume of vinegar used
The amount of bubbling observed
The conclusion you write
The number of bubbles produced

Time

Observation

Before mixing

Clear liquid; white powder is separate.

First 10 seconds

Rapid fizzing and many bubbles appear.

After 1 minute

Fizzing slows; some powder has disappeared.

Read the evidence

Use the observation record above for Questions 3–6.

3.Which observation is the clearest evidence that a gas formed?

4.True or false: The powder disappearing by itself proves that a chemical change occurred. Explain your choice.

5.Complete the sentence: In a chemical change, particles are rearranged to make substances with different properties.

6.Is the vinegar and bicarbonate reaction best described as a physical change or a chemical change? Use two observations as evidence.

7. Draw a simple particle model showing particles before and after a chemical reaction. Use labels or a key to show that atoms are rearranged, not destroyed. Your drawing should include at least two different kinds of atoms.

Apply your understanding

A chemical change is not identified by one sign alone. Bubbles can sometimes come from boiling, for example, so consider what caused them and look for evidence in context.

7.Classify each change as physical (P) or chemical (C): (a) an ice cube melting, (b) iron rusting, (c) a sheet of paper being cut, (d) bread toasting.

8.A student repeats the test but uses 60 mL of vinegar and two teaspoons of bicarbonate of soda. Why might the results be difficult to compare with the first test?

9.Suggest one safe improvement that would make the investigation's results more reliable. Explain how it would help.