What is the concentration in moles dm^-3 of ...

What is the concentration in moles dm^-3 of ...
10g of FeSO4.(NH4)2SO4.6H20 in 250cm^3 of solution?
for this one i did 10g /392(molar mass) = 0.03 mole
so there 0.03 mole of FeSO4.(NH4)2SO4.6H2O in 0.25dm^3 of solution
so 0.03/0.25 = 0.12mol.dm^-3
is that right?

What is the concentration in moles dm^-3 of ...
240cm^3 of NH3(g) dissolved in 1000cm^3 of solution ?

i worked out the mass of NH3 which is 17
and i need to find out how many moles of NH3 in 240cm^3,
do i need to convert the 240cm^3 into grams? how?

For the first question your process is spot on.
For the ammonia solution you nees to consider the volume of 1 mole of gas at rtp is 24dm3 - so how many moles in 240cm3?
You don't nees to consider mass.

1 don't think 10/392 = 0.03.

You know I mole of any gas at STP is 24dm3

thankyou

so is this right ?
240/17=14mole
so theres 14 mole of NH3 dissoled in 1dm^3 of solution
so 14/1 = 14 mol.dm^-3

10/392 when rounded is o.03

Sorry no.
The moles is 240cm3/24000cm3 =0.01 moles.
When calculating moles of gas from its volume you dont need the molar mass

10/392 when rounded is o.03

First you need to use the fact that 1 mole of any gas at 298K and 1 atm pressure occupies 24.0 dm3 (or 24000 cm3).

The volume of gas you have used was 240cm3. Hence you have used 240/24000 moles.

When using VOLUME of a gas to calculate moles, you must use molar volume.
Don't try to use molar mass or convert into mass.

When given the MASS, even of a gas, use the molar mass to calculate moles.

so how do i calculate the molar volume

Molar volume of a gas is 24dm3 (at 298K and 1 atm.)

so would this be right
240/1000 = 0.24dm3
0.24dm3/24=0.01moles
0.01=1=0.01mol.dm-3

Yes, spot on.