A mixture of magnesium bromide and magnesium sulfate is known to contain 3 moles of magnesium ions and 4 moles of bromide ions - Scottish Highers Chemistry - Question 6 - 2022

To find the number of moles of magnesium ions, we note that magnesium sulfate ( ext{MgSO}_4) contains 1 magnesium ion per formula unit. Given that there are 3 moles of magnesium ions total, the moles of magnesium sulfate can be calculated as:

$ext{Moles of MgSO}_4 = 3 - 2 = 1 \text{ mole of MgSO}_4$

Since each mole of magnesium sulfate produces one mole of sulfate ions, the moles of sulfate ions present are:

$\text{Moles of sulfate ions} = 1 \text{ mole of MgSO}_4 = 1 \text{ mole of SO}_4^{2-}$