a solution of sulfur (2.560g) in naphthalene (100g) freezes 0.68K lower the freezing point of pure naphthalene (353.10K). for naphthalene, Kf= 6.8K kg mol. calculatem the molecular formula of the sulfur dissolved in the naphthalene?
delta = Kf*molality
Solve for molality
molality = moles/kg solvent.
Solve for moles
moles = grams/molar mass
solve for molar mass.
so, 0.68K/6.8 K kg mol= 0.1kg/mol (m)
then 0.1/32g/mol= 3.1*10^-3
then (3.1*10^-3)*(2.56g)= 8*10^-3
does that make it S8, i don't get that part.
To find the molecular formula of sulfur dissolved in naphthalene, we need to use the concept of molality and freezing point depression.
We can start by calculating the molality of the sulfur solution using the formula:
Molality (m) = (moles of solute) / (mass of solvent in kg)
First, we need to find the moles of sulfur. We can do this by dividing the mass of sulfur by its molar mass. The molar mass of sulfur is 32.06 g/mol.
moles of sulfur = mass of sulfur / molar mass of sulfur
= 2.560 g / 32.06 g/mol
Next, we calculate the mass of the solvent (naphthalene) in kilograms by dividing the given mass (100g) by 1000.
mass of solvent (naphthalene) = 100 g / 1000
= 0.100 kg
Now, we can calculate the molality using the formula:
m = moles of solute / mass of solvent in kg
= (2.560 g / 32.06 g/mol) / 0.100 kg
Note: The units of molality should be in mol/kg, so we need to convert the grams to moles and the kilograms to grams.
m = ((2.560 g / 32.06 g/mol) / 0.100 kg) * (1000 g/1 kg)
= 0.799 mol/kg
Now, we can use the freezing point depression equation to find the change in freezing point. The equation is:
ΔT = Kf * m * i
Where:
ΔT = change in freezing point (0.68 K)
Kf = freezing point constant for naphthalene (6.8 K kg/mol)
m = molality (0.799 mol/kg)
i = Van't Hoff factor (the number of particles formed per molecule when the solute is dissolved)
Since sulfur does not dissociate in the solvent, its Van't Hoff factor (i) is 1.
Now, we can substitute into the formula to find the molecular formula of sulfur in naphthalene.
0.68 K = (6.8 K kg/mol) * (0.799 mol/kg) * 1
To isolate the number of moles of sulfur, divide both sides of the equation by the value of the constant:
0.68 K / (6.8 K kg/mol) = 0.799 mol/kg
Finally, we can calculate the number of moles of sulfur:
moles of sulfur = (0.68 K / (6.8 K kg/mol)) / 0.799 mol/kg
Now, we need to determine the molecular formula of sulfur by dividing the number of moles by the empirical formula molar mass (32.06 g/mol).
molecular formula of sulfur = (0.68 K / (6.8 K kg/mol)) / 0.799 mol/kg / 32.06 g/mol
Simplifying the expression will give you the molecular formula of sulfur dissolved in naphthalene.
1st step:
*Find out MB
*If the ans is less than ,64
For eg,
ans=32
So,64/32=2
Hence the formula is S2