# Unit 3 calculation questions

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#1
Q/ A mixture of magnesium bromide and magnesium sulfate is known to contain 3mol of magnesium and 4mol of bromide ions. How many moles of sulfate ions are present?
I am totally lost on how to do this question.
0
2 years ago
#2
Weird question but here is what I think. We know that we have a mixture containing compounds whose chemical formulae are MgBr2 (Magnesium Bromide) and MgSO4 (Magnesium Sulphate).

We know that there are 3 mol of Mg present however these 3 moles would account for both compounds as both contain Mg. We however know that 4 mol of Br- is present. These 4 mol of Br- is only found in the MgBr2 that is present. As there is 4mol of Br-, there is therefore overall 2 mol of MgBr2. This can be imagined as Mg(2+) + 2Br(-) —> MgBr2.

So this accounts of 2mol of Mg being present in MgBr2 leaving 1 mol of Mg in MgSO4. The formation of MgSO4 can be written as Mg(2+) + SO4(2-) —-> MgSO4. Thus there is a 1:1 ratio of MgO4, meaning there would be 1 mol of SO4(2-) ions in the solution I believe.
1
#3
Ok thanks!
0
2 years ago
#4
(Original post by wombat746)
Weird question but here is what I think. We know that we have a mixture containing compounds whose chemical formulae are MgBr2 (Magnesium Bromide) and MgSO4 (Magnesium Sulphate).

We know that there are 3 mol of Mg present however these 3 moles would account for both compounds as both contain Mg. We however know that 4 mol of Br- is present. These 4 mol of Br- is only found in the MgBr2 that is present. As there is 4mol of Br-, there is therefore overall 2 mol of MgBr2. This can be imagined as Mg(2+) + 2Br(-) —> MgBr2.

So this accounts of 2mol of Mg being present in MgBr2 leaving 1 mol of Mg in MgSO4. The formation of MgSO4 can be written as Mg(2+) + SO4(2-) —-> MgSO4. Thus there is a 1:1 ratio of MgO4, meaning there would be 1 mol of SO4(2-) ions in the solution I believe.
I got the same!
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