Question

Let two elements a and b combine to form two compounds ab and ab2. If 0.2 mole of ab weighs 20 g and 0.15 mole of ab2 weighs 24 g then atomic weights of a and b respectively are

Answer 1

Answer:

ab=w/m

0.2=20/m

m=20/0.2=100

ab2=w/m

0.15=24/m

m=160

from above. ab=100

a=100/b•••••••[eq 1]

ab2=160

b2=160/a

b2 =160 ×b

100

b2 =16

b. 10

so....

b=1.6 g.

put this in (eq ..1)

a=100/1.6

a=62.5 g

Hope this will help u. :)

Answer 2

Answer:

The atomic weights of 'a' and 'b' are 40gmol⁻¹ and 60gmol⁻¹ respectively.

Explanation:

Consider that the atomic weight of element a is X gmol⁻¹ and the atomic weight of element b is Y gmol⁻¹.

Given, the weight of compound 'ab' = 20g

The weight of compound 'ab₂' = 24g

The molar mass of compound 'ab' is equal to = X + Y

The molar mass of compound 'ab₂' is equal to = X + 2Y

We know that, $Number \; \; of \; moles =\frac{Given \; weight }{molar \; mass}$

For  compound 'ab':-   $0.2=\frac{20}{X+Y}$

$X+Y=100$                                                       ...............(1)

For compound 'ab₂' :- $0.15=\frac{24}{X+2Y}$

$X+2Y=160$                                                     ...............(2)

Subtract the equation (1) from equation (2):

$2Y-Y=160-100\\Y=60$

Substitute the value of Y in equation (1), we will get;

$X=100-60\\X=40$

Therefore, the atomic weight of element a is 40gmol⁻¹  and element b is 60gmol⁻¹ .