Asked by Bri
                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
            
        I posted this yesterday but I got the wrong answer and could use some step by step help?
Thanks
Answers
                    Answered by
            DrBob222
            
    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.
    
                    Answered by
            Bri
            
    when Im getting my Kf do i change it from Celsius to Kelvin before i do my calculation?
    
                    Answered by
            DrBob222
            
    You can but it doesn't matter. I think Kf for camphor is about 38 C/m (37.7 maybe?) or something like that.
    
                    Answered by
            DrBob222
            
    What I meant was that Kf for camphor is 37.7 celsius/m or 37.7 Kelvin/m
    
                    Answered by
            Bri
            
    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
    
deltaT=Kfm
m=mols solute/ kg solvent
1.56g vitamin k/83.8g= 0.019
m=0.019/ 0.025 = 0.76
                    Answered by
            Anonymous
            
    delta T=Kfm
-5.23=37.8m
-5.23-37.8 =m
m=-43.03
    
-5.23=37.8m
-5.23-37.8 =m
m=-43.03
                    Answered by
            DrBob222
            
    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.
<b>I don't think you followed the steps.</b>
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 = ?
    
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.
<b>I don't think you followed the steps.</b>
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 = ?
                    Answered by
            DrBob222
            
    nope. That isn't the way math works. 
    
                    Answered by
            Anonymous
            
    so i do 0.00346mols x 1.56 = 0.00539?
    
                    Answered by
            DrBob222
            
    no.
0.00346 mols = 1.56g/molar mass
molar mass = 1.56/0.00346 =?
    
0.00346 mols = 1.56g/molar mass
molar mass = 1.56/0.00346 =?
                    Answered by
            DrBob222
            
    I see I spelled anonymous wrong. 
    
                    Answered by
            Bri
            
    Thanks so so much! I was really confusing myself! The steps really helped!
    
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