Multiple choice Q4 2001
Posted 27 May 2007 - 11:56 AM
Posted 27 May 2007 - 05:02 PM
NaBr and Na2SO4
The question tells you that you have 2 moles of Bromide ions, hence NaBr means that you also have 2 moles of Sodium in NaBr
You have a total of 5 moles of sodium, so 5-2=3, 3 sodiums left for the sodium sulphate
(Na)2 has 3 moles, so the sulphate must have 1.5
Posted 28 May 2007 - 02:54 PM
Posted 28 May 2007 - 03:07 PM
EDIT: Actually I think I can see it anyway.
NaBr comes from Na + Br ---> NaBr
Therefore there is one mole of Na and one mole of Br in every mole of NaBr
Therefore if you have two moles of Br, you have two moles of NaBr therefore you have 2moles of Na. Hope this helps
Posted 26 April 2008 - 03:59 PM
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?
Formula for sodium bromide is NaBr
The Na and Br ions are in a ration of 1:1, hence if, like the question states there are 2 mol Br ions, there will also be 2 mol Na ions.
Formula for sodium sulphate is Na2SO4.
Since the question states that in total in the mixture there are 5 mol of Na ions, that means there are 3 mol Na ions in the sodium sulphate (2 from NaBr and 3 from Na2SO4 = 5 mol Na ions)
Since the ratio is 2:4 or 1:2 for the Na2SO4 we have to divide 3 by 2 to get the no. of sulphate ions present;
3/2 = 1.5 moles
Hence the answer is A
I used to have a problem with this type of question, but my teacher showed me the method above, so i hope it helps.
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