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Posted by MissChemTeacher_Bitesize (U15172316) on Sunday, 18th November 2012
A wee multiple choice question to get you thinking about Chemistry:
A mixture of sodium bromide and sodium sulphate is known to contain 5 mol of sodium and 2 mol of bromide ions.
How many moles of sulphate ions are present?
If you need help with the working post a message on the board.
I'll put a solution up in a few days.
Posted by MissChemTeacher_Bitesize (U15172316) on Sunday, 25th November 2012
You need to use the valency cross over method to write the formula for each of the compounds:
sodium bromide is NaBr
sodium sulphate is Na₂SO₄
This information can then be used to work out how many moles of ions there are in each of the compounds.
Na : Br
2 <-- 2 (2 moles of bromide ions (from the Q) will give us two moles of sodium ions from the sodium bromide in our container.)
3 -->1.5 (we have 3 moles of sodium ions left over in the mixture (we had 5 to start off with) as the ratio of sodium to sulphate ions is 2 ---> 1 we can conclude that the number of moles of sulphate ions is 1.5).
The answer is A.
Hope this helps
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