Question

(b) state two pieces of evidence which show that a chemical reaction is taking place when magnesium is burnt.
1.

2.
2
(c) in the experiment below, 2.4 g of grey magnesium ribbon is burnt in 3.2 g of colourless oxygen gas. all the magnesium and oxygen fully react with each other.

state the mass of magnesium oxide formed in the reaction. explain your answer.

2

Explanation:

Part (b)

To determine evidence of a chemical reaction when magnesium burns, we recall indicators of chemical changes.

1. Magnesium burns with a bright white light (light emission is a sign of energy change in a reaction).
2. A new substance (magnesium oxide, a white solid) is formed, different from the original magnesium (grey ribbon) and oxygen (colourless gas).

Step 1: Recall the Law of Conservation of Mass

The law states that in a chemical reaction, the total mass of reactants equals the total mass of products (no mass is created or destroyed).

Step 2: Identify Reactants and Their Masses

Reactants: Magnesium (\(2.4\ \text{g}\)) and Oxygen (\(3.2\ \text{g}\)).

Step 3: Calculate Total Mass of Reactants

Total mass of reactants \(= 2.4\ \text{g} + 3.2\ \text{g} = 5.6\ \text{g}\).

Step 4: Relate to Product Mass

Since all reactants fully react, the mass of the product (magnesium oxide) equals the total mass of reactants (by the Law of Conservation of Mass).

Answer:

1. Magnesium burns with a bright white flame (light is produced).
2. A white solid (magnesium oxide) is formed (new substance).

Part (c)