Vitamin K is involved in normal blood clotting. When 1.56 g of vitamin K is dissolved in 25.0 g of camphor, the freezing point of the solution is lowered by 5.23 °C. . Calculate the molar mass of vitamin K.

I posted this yesterday but I got the wrong answer and could use some step by step help?

Thanks

User Icon for DrBob222 DrBob222 answered
10 years ago

I think I answered your question. The easy way to find the error is for you to post your work and let me check it. I'm happy to do that for you.

User Icon for Bri Bri answered
10 years ago

when Im getting my Kf do i change it from Celsius to Kelvin before i do my calculation?

User Icon for DrBob222 DrBob222 answered
10 years ago

You can but it doesn't matter. I think Kf for camphor is about 38 C/m (37.7 maybe?) or something like that.

User Icon for DrBob222 DrBob222 answered
10 years ago

What I meant was that Kf for camphor is 37.7 celsius/m or 37.7 Kelvin/m

User Icon for Bri Bri answered
10 years ago

Im sure i did this wrong but this is what i did

deltaT=Kfm
m=mols solute/ kg solvent

1.56g vitamin k/83.8g= 0.019

m=0.019/ 0.025 = 0.76

User Icon for Anonymous Anonymous answered
10 years ago

delta T=Kfm

-5.23=37.8m
-5.23-37.8 =m
m=-43.03

User Icon for DrBob222 DrBob222 answered
10 years ago

I think I wrote this:

delta T = Kf*m
Substitute and solve for m = molality

m = mols solute/kg solvent
Substitute and solve for mols solute.

mols = grams/molar mass
Substitute and solve for molar mass.
I don't think you followed the steps.

Take it one step at a time.
delta T = K*m
5.23 = 37.7*m
m = 5.23/37.7 = about 0.138m

Next.
m = mols solute/kg solvent
0.138 = mols solute/0.025
mols solute = 0.138 x 0.025 = about 0.00346 mols

Next:
mol = grams/molar mass
0.00346 mols = 1.56g/molar mass
molar mass = ?

User Icon for DrBob222 DrBob222 answered
10 years ago

nope. That isn't the way math works.

User Icon for Anonymous Anonymous answered
10 years ago

so i do 0.00346mols x 1.56 = 0.00539?

User Icon for DrBob222 DrBob222 answered
10 years ago

no.

0.00346 mols = 1.56g/molar mass
molar mass = 1.56/0.00346 =?

User Icon for DrBob222 DrBob222 answered
10 years ago

I see I spelled anonymous wrong.

User Icon for Bri Bri answered
10 years ago

Thanks so so much! I was really confusing myself! The steps really helped!