This is an incomplete question, here is a complete question.
A compound is 42.9% C, 2.4% H, 16.7% N and 38.1% O by mass. Addition of 6.45 g of this compound to 50.0 mL benzene, C₆H₆ (d= 0.879 g/mL; Kf= 5.12 degrees Celsius/m), lowers the freezing point from 5.53 to 1.37 degrees Celsius. What is the molecular formula of this compound?
Answer : The molecular of the compound is,
Explanation :
First we have to calculate the mass of benzene.
Now we have to calculate the molar mass of unknown compound.
Given:
Mass of unknown compound (solute) = 6.45 g
Mass of benzene (solvent) = 43.95 g = 0.04395 kg
Formula used :
where,
= change in freezing point =
= freezing point of solution
= freezing point of benzene
Molal-freezing-point-depression constant for benzene =
m = molality
Now put all the given values in this formula, we get
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given.
Mass of C = 42.9 g
Mass of H = 2.4 g
Mass of N = 16.7 g
Mass of O = 38.1 g
Molar mass of C = 12 g/mole
Molar mass of H = 1 g/mole
Molar mass of N = 14 g/mole
Molar mass of O = 16 g/mole
Step 1 : convert given masses into moles.
Moles of C =
Moles of H =
Moles of N =
Moles of O =
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For C =
For H =
For N =
For O =
The ratio of C : H : N : O = 3 : 2 : 1 : 2
The mole ratio of the element is represented by subscripts in empirical formula.
The Empirical formula =
The empirical formula weight = 3(12) + 2(1) + 1(14) + 2(16) = 84 gram/eq
Now we have to calculate the molecular formula of the compound.
Formula used :
Molecular formula =
Therefore, the molecular of the compound is,
