Ok to answer this question we firsst need to fin the number of mol of Urea (CH4N2O). to do this we simply :
1 mol of urea =15/60.055 = 0.25mol
therefore 200g of water contain 0.25mol
the next step is to determine the malality of our solution in 200g of water, to do this we say:
200 g = 1Kg/1000g = 0.2kg
therefor 0.25mol/0.2Kg = 1.25mol/kg
and from the equation:
we know that i = 1
we are given Kf
b is the molality that we just calculated
therefore;
the solutions freezing point is -2.325°C
Number of moles is defined as the ratio of given mass in g to the molar mass.
The mathematical formula is:
Number of moles = (1)
Number of zinc atoms is equal to , by Avogadro number, number of moles can be calculated.
As, 1 mol= atoms, hence,
= 0.2822 mol
Now, from formula (1), calculate mass in g (molar mass of zinc = 65.4 g/mol)
0.2822 mol =
mass in g =
= 18.45588 g
Thus, by rounding off the above number, it will come near about 19 g approximately.
Hence, option (C) is the correct answer.