Unit 1/2 Chemistry question

[acciotardis]

I've only just realised how confused i am on some aspects of the mol.
This is a 2009 STAV paper question:

"A household cleaning agent contains a weak base of general formula NaX. 1g of this compound is dissolved into deionised water to make 100ml. 20ml samples of this solution were titrated with 0.100M HCl(aq) and required an average titre of 24.4ml of the acid for neutralisation. Determine the molar mass of the base."

I understand how to get the mol of HCL (0.00244mol). The next part confuses me when the worked solutions say:
"n(NaX) in 20ml = n(HCl) = 0.00244mol
n(NaX) in 100ml = 5 x 0.0024mol"

why do we multiply the mol by 5? I assumed it would be the same.

[sin0001]

No, the mol will stay the same if you simply add water to a solution, but in this case, you're taking part of something ( a fifth of something), this means you end up with a fifth of the original amount of that substance (i.e. fifth of the mols)

[morantz]

I've only just realised how confused i am on some aspects of the mol.
This is a 2009 STAV paper question:

"A household cleaning agent contains a weak base of general formula NaX. 1g of this compound is dissolved into deionised water to make 100ml. 20ml samples of this solution were titrated with 0.100M HCl(aq) and required an average titre of 24.4ml of the acid for neutralisation. Determine the molar mass of the base."

I understand how to get the mol of HCL (0.00244mol). The next part confuses me when the worked solutions say:
"n(NaX) in 20ml = n(HCl) = 0.00244mol
n(NaX) in 100ml = 5 x 0.0024mol"

why do we multiply the mol by 5? I assumed it would be the same.

In this instance, 100ml goes into 20ml five times, doesn't it? The reason why you have to mulitply the amount of mol given by 5 is because the amount of molecules within the solution will increase five times. Therefore, 20ml of NaX will yield 0.00244 mol, 100ml will have 5 times as many mols, hence it's 0.012 mol.

[acciotardis]

Alright! Thanks guys