International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

How can you determine which metal is more reactive when testing in acid?

1. Measure the temperature change

2. Count the number of bubbles produced

3. Observe the color change

4. Weigh the test tubes before and after

The correct answer is: Count the number of bubbles produced

To assess the reactivity of metals in acid, counting the number of bubbles produced during the reaction is a reliable method. When a metal reacts with acid, hydrogen gas is generated as a product. This gas forms bubbles, and the rate of bubble formation can indicate how quickly the reaction is occurring. Generally, more reactive metals will react more vigorously, producing a greater volume of hydrogen gas and, consequently, more bubbles within the same period. The other methods do not provide a direct comparison of reactivity. Measuring temperature change might show differences in how much heat is released, but it doesn't directly correlate with the degree of reactivity. Observing a color change could indicate a chemical reaction, but it isn't specific to the reactivity of metals with acid, as not all metal-acid reactions produce color changes. Weighing the test tubes before and after the reaction can provide information about mass loss or gain due to the reaction, but this isn't a straightforward indicator of reactivity as it doesn't quantify the intensity of the reaction itself. Therefore, counting the number of bubbles is the best approach to determine which metal is more reactive when testing in acid.