O Level Chemistry: Challenging Mole Calculation Questions

09 May

Posted by: sean in: Chemistry Notes & Tips

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Recently, i received several emails and comments from readers (students) to share more challenging Mole Calculations (or Mole Concepts) questions in this chemistry blog. So here we go………..

Question:

What would be the concentration of the hydrochloric acid produced if all the hydrogen chloride gas from the reaction between 50g of pure sulfuric acid and an excess of sodium chloride was collected in water, and the solution made up to a volume of 400 cm3 of water?

Based on equation: NaCl(s) + H2SO4(aq) –> NaHSO4(s) + HCl(g)

Now, try it out and leave your suggested answer (and possibly your solution/steps) in the comment section below.

The best way to learn is NOT by reading or looking, instead it is by Taking Actions.

I look forward to seeing you answers. Cheers! Enjoy! =)

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10 Responses

Chemistry genius
09|May|2010 1

50/98=0.5102
0.5102/(400/1000)= 1.28mol/dm3

Reply
taimoor
09|May|2010 2

27.40 mol/dm3

Reply
Awesomus
12|May|2010 3

It’s 1.28 mol/dm3

Reply
budding chemist
17|May|2010 4

What would be the concentration of the hydrochloric acid produced if all the hydrogen chloride gas from the reaction between 50g of pure sulfuric acid and an excess of sodium chloride was collected in water, and the solution made up to a volume of 400 cm3 of water?

Based on equation: NaCl(s) + H2SO4(aq) –> NaHSO4(s) + HCl(g)

mole=50/(2+32+(16×4))=0.5102
mol/dm3=0.5102/(400/1000)=1.28mol/dm3

Reply
Saud
20|May|2010 5

yeah i agree with the majority….
its 1.28mol/dm3

mass of sulfuric acid = 50g
relative formula mass of sulfuric acid = 98
so,
moles of sulfuric acid = mass/molar mass
= 50/98
= 0.51 moles

keeping in view the stoichometric ratios of the reactants and the products we get that one mole of sulfuric acid results one mole of HCl…

given also that the solution was made upto 400 cm3
that means that the moles of HCl in 400cm3 are 0.51

how much will these be in 1000cm3 i-e 1dm3
that is

=1000/400 x0.51
=1.275 moles in 1dm3
approximating it to 2 decimal places

concentration of HCl = 1.28 mol/dm3

Reply
Saud
20|May|2010 6

i don’t get that why others have divided 0.51 with 400/1000 …… ??

guide me guys…………..

Reply
kazim Reply:
May 23rd, 2010 at 9:25 pm
its because the concentration is in mol./dm3, but the volume of water given is in cm3 so we divide it by 1000 to convert it into dm3. =D

Reply
Karl Reply:
May 25th, 2010 at 11:58 pm
@Saud – you are correct, don’t worry.

Reply
abhishek
23|May|2010 7

1.28 mol/dm3

Reply
yumi
01|Jun|2010 8

1.28 mol/dm3 (to 3 sf)

Reply