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Chemical Reactions Investigation

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Chemical Reactions Investigation

A community science team is testing three reactions to decide which observations provide reliable evidence of chemical change. Read the investigation brief and data, then analyse the results. Use evidence from the data in your explanations.

Investigation brief and data

The team mixed equal measured amounts of each reactant at room temperature. For Reaction A, magnesium ribbon was added to dilute hydrochloric acid. For Reaction B, sodium hydrogen carbonate (baking soda) was mixed with vinegar (dilute ethanoic acid) in an open beaker. For Reaction C, a few drops of iodine solution were added to starch solution. They recorded the observations below. No numerical mass measurements were taken.

Reaction

Starting temperature

Final temperature

Observations

A: magnesium + dilute hydrochloric acid

22.0 °C

31.5 °C

Steady bubbles; magnesium became smaller; solution stayed clear.

B: sodium hydrogen carbonate + vinegar

22.0 °C

18.5 °C

Rapid fizzing; mixture became cooler; no solid remained.

C: iodine solution + starch solution

22.0 °C

Mixture changed from cloudy white to dark blue-black; no bubbles.

Interpret the evidence

For each answer, distinguish an observation (what was noticed) from an inference (what it may mean).

1.Which option lists two observations from Reaction A that are evidence consistent with a chemical reaction?

The solution stayed clear and the acid was dilute.
Bubbles formed and the temperature rose.
The magnesium became smaller and the starting temperature was 22.0 °C.
The mixture was in a beaker and the solution stayed clear.

2.Reaction B became cooler. Is a temperature decrease evidence that a reaction occurred? Explain why temperature change alone does not identify the products.

3.In Reaction C, the colour changed but the temperature did not. Explain why a colour change can be evidence of chemical change, and state one reason it is not conclusive on its own.

4.Match each reaction with its most likely gas product or colour-test result. Use each right-hand option once.

A: magnesium + hydrochloric acid
B: sodium hydrogen carbonate + vinegar
C: iodine solution + starch solution

Carbon dioxide gas
Hydrogen gas
Blue-black starch–iodine complex

5.Write a balanced symbol equation for Reaction A. Include state symbols if you know them.

6.Reaction B fizzed in an open beaker. A student claims, “The mass of the beaker and its contents must increase because new gas was made.” Explain the error in this claim using conservation of mass.

7.A team wants to compare how quickly magnesium reacts with acid at different temperatures. Identify the independent variable, the dependent variable, and two variables they should keep constant.

8.Evaluate the investigation data: give one strength of the method and one limitation that makes the conclusions less reliable. Suggest a practical improvement.

9.True or false: Reaction C must have released or absorbed heat because it produced a dramatic colour change. Give a reason for your choice.

TrueFalse