Question

The boiling point of a solution containing 0.20g of a substance X in 20.00g of ether is 0.17k higher than that of pure ether calculate the molecular mass of X boiling point constant of Ether per 1kg is 2.16k

Answer 1

Answer:

hey mate !! here is your answer..

Explanation:

ΔT

b

=K

b

×m=K

b

×

Mass of solvent in kg

n

solute

0.1=2.16×

Molar Weight

0.11

×

0.015

1

Molar Weight=

0.015×0.1

2.16×0.11

=158.4

Hence, the correct option is B

Answer 2

The molecular mass of solute is 127 g/mol.

Explanation:

Given the boiling point of a solution of ether and substance, X = 0.17 K higher than pure ether.

Thus,  Δ$T_b$ = 0.17 K

It is also given that mass of substance X = 0.20 g

Mass of solvent ether, M = 20 g

and Boiling point constant $K_b$ for ether = 2.16 K/kg

Now, we know that Elevation in boiling point$\Delta T_b = K_b\times m$

And m stands for molality and is equal to the number of moles per kg of solvent.

First calculating m

$m = \frac{n}{M}$

and number of moles (n) is the amount of solute (in g) divided by its molar mass

$n =\frac{0.2}{X}$

So, m becomes

$m = \frac{0.2/X}{20/1000}$

or

$m = \frac{0.2\times 1000}{20\times X}$

$m = \frac{200}{20\times X}$

$m = \frac{10}{X}$

Thus, $\Delta T_b = K_b\times m$

$0.17 = 2.16(\frac{10}{X})$

$X = \frac{21.6}{0.17}$

$X = 127$