(a) A solution of 2.000 g of the compound Y(CH6N2O5) dissolved in 40.00 g water has a freezing point of -2.38 degree C. What is the molar mass of the compound Y(CH6N2O5) ? what is the implication of this molar mass? (Given that the freezing point depression constant Kf of water is 1.86 degree C/m.)
dT = Kf*m
2,38 = 1.86*m
m = ?
Then m = #mols/kg solvent
m = #mols/0.04 = ?m
#mols = grams/molar mass
# mols = 2.00/molar mass
Solve for molar mass. I have approximately 39
With a formula of CH6N2O5 we're looking at about 126. The implications is that compound Y must not be ionized to some degree. For example:
If it were ionized into two particles then
2.38 = i*Kf*m. Go through the calculations and
molar mass = 78 etc
And
(b) Predict which would e cheaper for preparing an antifreeze solution, after adding the following solutes (given that they sold at the same price per pound): 0.15 m Pb(ClO3)2 or unknown compound Y(CH6N2O5) stated above? Answer:_________
Why?
ok, I also counted 39 in (a)
actually I am so sorry that I tape a wrong compound, compound Y should be CH6N2O2 , will it have same explain in (b)?
Yes and no and I wondered about that when I responded to the initial question. In this case note that the CH6N2O2 adds up to 78 which is exactly twice the 39 we obtained for the molar mass. That means that i in
dT = i*Kf*m is 2 so the compound has ionized into two particles. This makes a lot more sense.
To calculate the molar mass of the compound Y(CH6N2O5), we can use the formula:
Molar mass (g/mol) = (mass of solute) / (moles of solute)
First, we need to calculate the moles of solute dissolved in the water. We can use the formula:
moles of solute = (mass of solute) / (molar mass of solute)
Given:
Mass of solute (Y(CH6N2O5)) = 2.000 g
Mass of solvent (water) = 40.00 g
Freezing point depression constant of water (Kf) = 1.86 °C/m
Freezing point depression (ΔTf) = -2.38 °C
Step 1: Calculate the moles of solute
moles of solute = (mass of solute) / (molar mass of solute)
moles of solute = 2.000 g / molar mass of solute
Step 2: Calculate the moles of water
moles of water = (mass of solvent) / (molar mass of water)
The molar mass of water is approximately 18.015 g/mol.
moles of water = 40.00 g / 18.015 g/mol
Step 3: Calculate the molality of the solution
molality = moles of solute / (mass of solvent in kg)
mass of solvent in kg = 40.00 g / 1000 g/kg
Step 4: Calculate the freezing point depression (ΔTf) using the formula:
ΔTf = Kf * molality
Now, we have ΔTf and we know that ΔTf = -2.38 °C. We can rearrange the formula to solve for molality:
molality = ΔTf / Kf
Step 5: Rearrange the formula for molality to solve for moles of solute:
molality = moles of solute / (mass of solvent in kg)
moles of solute = molality * (mass of solvent in kg)
Now, we have all the information we need to calculate the molar mass of the compound.
molar mass of Y(CH6N2O5) = (mass of solute) / moles of solute
Substituting the values we have calculated, we can find the molar mass of the compound Y(CH6N2O5).