Hey could anyone explain to me how to do Q4 in 2001 multiple choice cos i know there is quite a few throughout all the past papers but i'm not sure how to do them.

thanks.

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# Multiple choice Q4 2001

Started by Acceptable in the 80's, May 27 2007 11:56 AM

6 replies to this topic

### #1

Posted 27 May 2007 - 11:56 AM

### #2

Posted 27 May 2007 - 04:46 PM

God ask for some help n get ignored awell lol

### #3

Posted 27 May 2007 - 05:02 PM

Here to help

Well

You Have;

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

Then

You have a total of 5 moles of sodium, so 5-2=3, 3 sodiums left for the sodium sulphate

then

(Na)2SO4

so

(Na)2 has 3 moles, so the sulphate must have 1.5

Well

You Have;

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

Then

You have a total of 5 moles of sodium, so 5-2=3, 3 sodiums left for the sodium sulphate

then

(Na)2SO4

so

(Na)2 has 3 moles, so the sulphate must have 1.5

Chemical Engineering - Edinburgh

*Conditional*### #4

Posted 27 May 2007 - 05:33 PM

Thank you for the help !

### #5

Posted 28 May 2007 - 02:54 PM

I dont understand. where does the 5 moles of Na come from? is there 2 moles of sodium ions in NaBr or 2 moles of Na or do you mean (Nabr)2?

### #6

Posted 28 May 2007 - 03:07 PM

If you post the question I will explain it for you

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

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

### #7

Posted 26 April 2008 - 03:59 PM

2001 multiple choice qu4

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

I used to have a problem with this type of question, but my teacher showed me the method above, so i hope it helps.

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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