Question

Two elements a and b form compounds having molecular formula ab2 and ab4

Answer 1

Explanation:

Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 Kwhereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 Kkg mol-1.

Answer 2

Answer:

atomic mass of A = 25.59 u Atomic mass of B = 42.6 u.

Explanation:

Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C6H6), 1 g of AB2 lowers the freezing point by 2.3 Kwhereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 Kkg mol-1. Calculate atomic masses of A and B.

Answer :

As We know that:

MB = (Kf x wB x 1000) / (wA X ΔTf)

Now ΔTf = 2.3 , wB = 1.0 , wA = 20, KF = 5.1 (given)

PUTTING THE VALUES IN THE EQUATION

MB = (5.1 x 1 x 1000) / (20 x 2.3) = 110.87 g/mol

Therefore MAB2 = 110.9

For AB4 compound

ΔTf = 1.3 , wb = 1 ,wa = 20

MB = (5.1 X 1 X 1000) / (20 X 1.3) = 196 g/mol

Therefore MAB = 196

Let x be the atomic mass of A & y be the atomic mass of B,

THEN MAB2 = x + 2y = 110.9 ----------------------------------(1)

And MAB = x + 4y = 196        ----------------------------------(2)

Subtracting 2 from 1 ,we get

2y  = 196-110.9

y   = 85.1 / 2 

y = 42.6

Putting the value of y in 1 we get

x = 110.9 - 2 x 42.6

x = 25.59

Therefore atomic mass of A = 25.59 u Atomic mass of B = 42.6 u.