2.21 Two elements A and B form compounds having formula AB2 and AB4 . When dissolved in 20 g of benzene of AB2 lowers the freezing point by whereas of AB4 lowers it by . The molar depression constant for benzene is Calculate atomic masses of A and B.

Name: Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C_6H_6), 1 g of AB2 lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K..
Uploaded: Thu, 2019-05-30 12:26
Description: Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C_6H_6), 1 g of AB2 lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K..

Two elements A and B form compounds having formula AB2 and AB4. When dissolved in 20 g of benzene (C_6H_6), 1 g of AB2 lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K..

2.21 Two elements A and B form compounds having formula AB₂ and AB₄ . When dissolved in 20 g of benzene of AB₂ lowers the freezing point by $2.3\; K$ whereas of AB₄ lowers it by $1.3\; K$ . The molar depression constant for benzene is Calculate atomic masses of A and B.

Answers (1)

In this question we will use the formula :

$\Delta T_f = k_f \times m$

Firstly for compound AB₂ :-

$M_B = \frac{K_f\times W_b \times 1000}{w_A\times \Delta T_f}$

or $= \frac{5.1\times 1 \times 1000}{20\times 2.3} = 110.87\ g/mol$

Similarly for compound AB₄ :-

$M_B= \frac{5.1\times 1 \times 1000}{20\times 1.3} = 196\ g/mol$

If we assume atomic weight of element A to be x and of element B to be y, then we have :-

x + 2y = 110.87 ----------------- (i)

x + 4y = 196 ----------------- (ii)

Solving both the equations, we get :-

x = 25.59 ; y = 42.6

Hence atomic mass of element A is 25.59u and atomic mass of element B is 42.6u.

Posted by

Devendra Khairwa

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2.21 Two elements A and B form compounds having formula AB2 and AB4 . When dissolved in 20 g of benzene of AB2 lowers the freezing point by whereas of AB4 lowers it by . The molar depression constant for benzene is Calculate atomic masses of A and B.

Answers (1)

Posted by

Devendra Khairwa

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2.21 Two elements A and B form compounds having formula AB₂ and AB₄ . When dissolved in 20 g of benzene of AB₂ lowers the freezing point by $2.3\; K$ whereas of AB₄ lowers it by $1.3\; K$ . The molar depression constant for benzene is Calculate atomic masses of A and B.