In a reaction, 9.2g of sodium reacted with 3.2g of oxygen gas to give 12.4g of sodium oxide. Balance the equation. (5 marks)

Here we need to balance the equation with moles because we don't know how many atoms are present. First, we need to work out the moles of each compound by dividing the mass by the Mr. By doing this, we'll see that an element double the number of moles more than others, making the ratio 4:1:2. We can now balance the equation, knowing that there are 4 Na, 1 C₇H₁₆, and 1O₂, but 2 Na₂O. = 4Na + O₂ → 2Na₂O