The Student Room Group
Use the formula: Concentration (mol dm-3) = moles (mol)/volume (dm3)

so for 1a) 0.05 mol dm-3 x 2 dm3 = 0.10 mol
Reply 2
Yearforever
Can someone tell me how to answer these type of questions:

Calculate the number of moles in the following.
1a) 2dm3 of 0.05 mole dm-3 HCL
b) 50 litres of 5 mol dm-3 H2SO4
c) 10 cm3 of 0.25 mol dm-3 KOH

Rep given :biggrin:


You know the equation moles=concentration x volume, right?

Why not use that? The volumes are 2dm3, 50 litres, etc, and the concentrations are 0.05 mole dm-3, 5 mol dm-3 , etc.

Simple. :smile:

[EDIT]...as Eier Von Satan says. :sigh:
Reply 3
james.h
You know the equation moles=concentration x volume, right?

Why not use that? The volumes are 2dm3, 50 litres, etc, and the concentrations are 0.05 mole dm-3, 5 mol dm-3 , etc.

Simple. :smile:

[EDIT]...as Eier Von Satan says. :sigh:


Thanks but do I need to convert 50 litres to dm? Or shall i just leave it?
Yearforever
Thanks but do I need to convert 50 litres to dm? Or shall i just leave it?


One litre is 1 dm3 :smile:
Reply 5
EierVonSatan
One litre is 1 dm3 :smile:


Thanks:biggrin: , by the way are the answers to b and c .... 250 mol and 2.5 mol?

http://www.chemsheets.co.uk/AS/CHEM1.2/AS.CHEM1.2.011.pdf

That's the sheet I'm practicing on:p:

I'm starting on number 2 but it says to give the following in both mol dm-3 and g dm-3.

For 2a) do i do:
0.400/2.00 x 1000 = 200 is that right?:confused:

PS: I've repped you :wink:
Yearforever
Thanks:biggrin: , by the way are the answers to b and c .... 250 mol and 2.5 mol?


Careful with the units with c it's given in cm3 (1/1000 dm3) but b is fine :smile:

For 2a) do i do:
0.400/2.00 x 1000 = 200 is that right?:confused:


:doh:
Reply 7
EierVonSatan
Careful with the units with c it's given in cm3 (1/1000 dm3) but b is fine :smile:



2a) concentration in mol dm-3 = 0.4 x 2 = 0.8

Then 0.8 x 36.5 (RMM of HCl) = 29.2 g dm-3


So is 29.5 and 0.8 both separate answers. Because it's say give answer in both mol and g:confused:
Yearforever
So is 29.5 and 0.8 both separate answers. Because it's say give answer in both mol and g:confused:


yes :smile:
Reply 9
EierVonSatan
Careful with the units with c it's given in cm3 (1/1000 dm3) but b is fine :smile:



2a) concentration in mol dm-3 = 0.4 x 2 = 0.8

Then 0.8 x 36.5 (RMM of HCl) = 29.2 g dm-3


ok thanks but why did 0.400 turn into 0.4?
Yearforever
ok thanks but why did 0.400 turn into 0.4?


They're the same thing :yes:
Reply 11
EierVonSatan
They're the same thing :yes:


oh how silly of me:p:

for 2b for mols is the answer 62.5 mol or 1562.5 mols?
:doh:

sorry earlier 2a) conc = mol/vol = 0.4/2 = 0.2 M => 0.2 x 36.5 = 7.3 g dm-3

2b) 12.5/5 = 2.5 M => 2.5 x 98 = 245 g dm-3
where did you get 36.5 from ?