This question is about metals and the reactivity series - AQA - GCSE Chemistry - Question 2 - 2020 - Paper 1

The pale grey crystals that form are silver, indicating that copper displaces silver from the silver nitrate solution. This happens because copper is more reactive than silver. The solution turning blue shows that copper ions are now in solution, confirming that copper has reacted and displaced less reactive silver.

1. Add the metals to dilute hydrochloric acid: Introduce small pieces of magnesium, iron, and copper into separate test tubes containing dilute hydrochloric acid.
2. Observe reactions: Check for signs of reaction, such as bubbling (indicating hydrogen gas production) or temperature change.
3. Record results: Note which metals react and which do not. For instance, magnesium will produce a vigorous reaction, iron will show some bubbling, and copper will show no reaction.
4. Control variables: Ensure that each test uses the same concentration and volume of hydrochloric acid, same mass of each metal, and same particle size for consistency. This plan should yield valid results that help identify each metal based on their reactions with the acid.

To calculate the relative atomic mass (A_r) of metal M, we use the formula: $A_r = \frac{(203 \times 30) + (205 \times 70)}{100}$ Calculating this gives: $A_r = \frac{6090 + 14350}{100} = \frac{20440}{100} = 204.4$ Thus, the relative atomic mass of metal M is 204.4.