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

1. 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?
2. (Original post by Chez 01)
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.
3. 1 don't think 10/392 = 0.03.

You know I mole of any gas at STP is 24dm3
4. (Original post by TutorsChemistry)
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.
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
5. (Original post by Maker)
1 don't think 10/392 = 0.03.

You know I mole of any gas at STP is 24dm3
10/392 when rounded is o.03
6. (Original post by Chez 01)
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
Sorry no.
The moles is 240cm3/24000cm3 =0.01 moles.
When calculating moles of gas from its volume you dont need the molar mass
7. (Original post by Chez 01)
10/392 when rounded is o.03
It is.
I believe Maker is questioning how many sf you should use.
8. (Original post by TutorsChemistry)
Sorry no.
The moles is 240cm3/24000cm3 =0.01 moles.
When calculating moles of gas from its volume you dont need the molar mass
I'm not understanding, could you explain how id calculate the concentration in this example please
9. 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.
10. (Original post by Chez 01)
10/392 when rounded is o.03
More like 0.025
11. (Original post by TutorsChemistry)
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
12. PV=nRT
13. (Original post by Chez 01)
so how do i calculate the molar volume
Molar volume of a gas is 24dm3 (at 298K and 1 atm.)
14. (Original post by TutorsChemistry)
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
15. (Original post by Chez 01)
so would this be right
240/1000 = 0.24dm3
0.24dm3/24=0.01moles
0.01=1=0.01mol.dm-3
Yes, spot on.
16. (Original post by TutorsChemistry)
Yes, spot on.
thankyou

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