Question

A solution of H2SO4(aq) with a molal concentration of 3.97 m has a density of 1.216 g/mL. What is the molar concentration of this solution?

Answer 1

I think you mean molality (m)?


molality = Moles of Solute/Kg of Solution

so we have,

3.97m = moles of H2SO4/ 1 Kg

Note: I picked 1kg of solution arbitrarily, it doesn't matter what volume you pick you will still get the same molarity.

solve for the moles of solute

3.97m * 1kg = moles of H2SO4
moles of H2SO4 = 3.97mol

so now we need to convert 1kg to mL of solution

1kg = 1000g

so set up the ratio,

1.216 g/mL = 1000g/xmL
1.216x = 1000
x = 1000/1.216
x= 822.37mL

Volume of solution = 822.37mL

1mL = 1000L

822.37mL/1000 = 0.82237L

Molarity = Moles of Solute (H2SO4)/Liters of Solution

Molarity = 3.97mol/0.82237L
Molarity = 4.83M

Answer 2

I wish I could edit posts,

Error 1:

Molality (m) = Moles of Solute/Kg of SOLVENT


Error 2:

"Note: I picked 1kg of solution arbitrarily, it doesn't matter what volume you pick you will still get the same molarity."

should be,

"Note: I picked 1kg of solvent arbitrarily, it doesn't matter what mass of solvent you pick you will still get the same molarity."

Answer 3

Mass of Solvent doesn't affect molarity in this case because moles is constant between both solutions as well as density is being used to convert the total Mass of Solvent to the total volume of Solution

Answer 4

In this case:

Solute is the H2SO4
Solvent is just the water (assuming that it is dissolved in water)

Answer 5

If you have any questions feel free to ask

Answer 6

If M =\[\frac{ mol }{ sol }\] or solute/ solution shouldn't we consider that molal concentration has the mass of solvent in the denominator whereas molar concentration has volume of solution in the denominator. Be sure to sum the masses of solute and solvent before applying the density.

Answer 7

yeah I made a mistake :S I'm rusty

Answer 8

but since you know that you should be able to determine the correct answer so meh

Answer 9

I'm actually doing this online and its not accepting my answer either.

Answer 10

ok well let me try to correct for it

Answer 11

xg/98.078g/mol = 3.97mol

3.97mol*98.078g/mol =389.4g

389.4g + 1000 = 1389.4g

1.216 = 1389.4g/x
1.216x = 1389.4
x = 1389.4/1.216
x = 1142.598mL
x = 1.142598mL

3.97mol/1.142598mL =3.475M

Answer 12

or

3.48M

Answer 13

I wrote mL instead of L by accident

Answer 14

is that correct?

Answer 15

yea that's it!!! Thanks, sorry for the late response I was trying to figure it out also.

Answer 16

No thank you for informing me about my mistake originally, this site is great for brushing up on my solution calculations while I'm trapped in university :S

Answer 17

if you have any questions about my math please inform me and I can explain it to you