AS Chemistry - Solutions Calculations

I'm not quite sure how to do these calculations or which formula to use. Any help please?

Calculate the amount of solute in 4.00dm3 of 5M NaOH

Calculate the mass of the solute in 1.00dm3 of 0.1M NaCl
For these sorts of questions can I just use m= (Mr*c*V)/1000 ?

Cheers.

Reply 1

Saf!

thelibertines

I'm not quite sure how to do these calculations or which formula to use. Any help please?

Calculate the amount of solute in 4.00dm3 of 5M NaOH

Calculate the mass of the solute in 1.00dm3 of 0.1M NaCl
For these sorts of questions can I just use m= (Mr*c*V)/1000 ?

Cheers.

by solute if you mean moles then:

moles (in a solution) = (VxC) / 1000

huh but i'm confused......isn't 4.00 dm3 and 5 M the conc??

Reply 2

thelibertines

OP

6

Saf!

by solute if you mean moles then:

moles (in a solution) = (VxC) / 1000

huh but i'm confused......isn't 4.00 dm3 and 5 M the conc??

If it was 4.00dm^-3 it would also be the concentration

I think that 4.00dm^3 refers to the volume...??

Reply 3

Saf!

oh yeh!....sorry my wrong....i didn't realise that 100dm3= 1cm3

A) anyway when using that equation volume has to be in cm3........so 4/100=0.04cm3

then

mol= (0.04 x 5) /1000
= 2 x 10^-4 mol (0.0002mol)

B) find the moles using the solutions equation.......and then find the Mr of NaCl and using the Mr and moles.......use the mol=mass/Mr equation to figure out the mass!

hope that helps! :smile:

Reply 4

thelibertines

OP

6

Oh right, I see now. Thanks! :biggrin:

your welcome!

OP

Wait a sec, isn't a decimetre a tenth of a metre, so it would be 4/10...?

Reply 7

hihihihi

Saf!

oh yeh!....sorry my wrong....i didn't realise that 100dm3= 1cm3

A) anyway when using that equation volume has to be in cm3........so 4/100=0.04cm3

1000 cm^3 = 1 dm^3
Eh, what are you trying to do here?

Reply 8

Willywonko

Eh. sorry to break it but you are just making a really simple question complicated: The concetration is given in moles/litre, and 1dm3 is actually a litre. Hence you have 5 moles of solute in each dm3, and since you have 4dm3, you will have 20 moles of solute

The second question is solved just the same way, 0.1 moles per dm3, and since you have 1dm3 of solution, you have 0.1 moles of solute.

Reply 9

thelibertines

OP

6

AS Chemistry - Solutions Calculations

Related discussions

Articles for you