# Chemistry

posted by .

Which aqueous solution below is expected to have the lowest freezing point? Assume 100% dissociation for ionic species.

1)0.25m MgBr2
2)0.30m Na2SO4
3) 0.50m KCl
4) 1.0m sucrose
5) 0.40m Cr(NO3)3

I think that the answer is 0.30NaSO4 but I am not positive. Is this correct?

Chemistry - DrBob222, Friday, February 10, 2012 at 11:21pm
delta T = i*Kf*m
You want the largest delta T (which will give the lowest freezing point).
Kf is constant so we can forget that. The two that matter are i and m
So multily i*m for the 5 and the largest number wins. Remember i is the van't Hoff factor which is the number of particles produced when the materials are placed in solution. sucrose is l. KCl is 2, etc.

Chemistry - Hannah, Saturday, February 11, 2012 at 12:22am
I understand everything except the van't Hoff factor part. I do not understand how you figure that out.

Chemistry - DrBob222, Saturday, February 11, 2012 at 12:44am
That how the material ionizes.
KCl ==> K^+ + Cl^- and i = 2
MgCl2 ==> Mg&2+ + 2Cl^- and i = 3
Na2SO4 == 2Na^+ + SO4^2- and i = 3
Cr(SO4)3 ==> Cr^3+ + 3SO4^2- and i = 4
Sugar doesn't ionize so it is just 1 particle
Sugar ==> sugar(aq) and i = 1

Chemistry - Hannah, Saturday, February 11, 2012 at 10:02am
Ok so then I just have to find the mass of each solution

so KCl = 74.55 X 2
MgBr2 = 184.11 X 3
Na2SO4 = 94.05 X 3
Cr(SO4)3 = 340.21 X 4

So Cr(SO4)3 would have the largest delta T, so the lowest freezing point.
Is this correct?

Chemistry - DrBob222, Saturday, February 11, 2012 at 3:01pm
Why do you need the molar mass?
delta T = i*Kf*m
You know i from my previous response and you know m from the problem. i*m that gives the largest number will be the one that gives the largest delta T.

Chemistry - Hananh, Saturday, February 11, 2012 at 10:46pm
Ok so do you mean 0.25MgBr2 X 3 = 0.75 ?

So I think that 0.40m Cr(NO3)3 has the largest delta T. Would you agree?

• Chemistry -

• Chemistry -

Thank you for all your help!!

## Similar Questions

1. ### chemistry

which of the following would be expected to have the lowest freezing temperature?
2. ### science

four flasks each contain 100 milliliters of aqueous solutions equal concentrations at 25 degress C and 1 atm. the four flasks are KCL,CH3OH, Ba(OH)2, and CH3COOH. the question is Which solution had the lowest freezing point and explain …
3. ### chemistry, freezing point depression

Hey guys I did a lab and I have to answer the questions relating to the lab. I did question 1 & 2, can someone check if they are correct, and question 3 I don't know how to do it. 1. Calculation to Determine the molecular weight of …
4. ### Chemistry

Assuming that each system behaves ideally, which solution (.25m KCl or .25m C3H8O3) would have the lower freezing point?
5. ### Chemistry

Calculate the boiling points of freezing points of the following solutions in water. a) boiling point of a 2.25m solution of propylene glycol (a non-electrolyte) b)freezing point of a 1.0m solution of potassium iodide c)freezing point …
6. ### Chemistry

Which solution will have the lowest freezing point?
7. ### Chemistry

Which aqueous solution below is expected to have the lowest freezing point?
8. ### Chemistry

If all ionic substances completely ionized, the aqueous solution with the lowest freezing point would be 1)0.25m NH4NO3 2)0.30m BaCl2 3) 0.35m LiBr 4) 0.50m Sucrose 5) 0.40m MgSO4 I know that i have to multiply m and i to find the …
9. ### chemistry

calculate the freezing point of an aqueous solution containing 10.50 g of MgBr2 in 200 g of water (MgBr2=184 g, Kf for water =1.80 K kg mol-1)
10. ### chemistry

I have the answers, I am just interested in the formulas so that I can solve the problems, thanks! 1. Find the boiling point of a solution composed of 110g of HgCl2 (a non-ionizing solute) in 175g of water. 2. Find the freezing point …

More Similar Questions