Question

Two elements A and B form compounds having formula AB2 and AB4 when dissolved in 20 of benzene 1g of AB2 lowers the freezing point by 2.3k whereas 1.0g of AB4 lowers it by 1.3k. The molar depression constant for benzene is 5.1kg mol-1 calculate atoms mass of A and B
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Answer 1

Explanation:

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Answer 2

Answer:

the atomic mass of a is 25.59 g/mol and b is 42.64 g/mol

Explanation:

As we know that,

MB=(kf×WB×1000)/(WA×deltaTf)

Now deltaTf =2.3, WB=1.0, WA=20,KF=5.1( given)

putting tye values in the equation.

MB=(5.1×1×1000)/(20×2.3)

=110.87 g/mol

Therefore Mab2=110.9

for AB4 compound

delta Tf=1.3,WB=1,Wa=20

MB=(5.1×1×1000)/(20×1.3)

=196g/mol

therefore MAB=196

Let x be the atomic masw of Aand y be the atomic mass of B

Then MAB2=x+2y=110.9______(1)

&MAB=x+4y=196________(2)

subtracting (2)from(1)

we get,

2y=196-110.9

y=85.1/2

y= 42.6

putting tye value of y in (1)

we get,

x=110.9 -2×42.6

x=25.59

Therefore, Atomic mass of A=25.59U and Atomic mass of B =42.6U.