Question

12.976g of lead combines with 2.004g of oxygen to form PbO2.PbO2 can also be produced by heating lead nitrate and it was found that the percentage of oxygen present in PbO2 is 13.38% . with the help of given information ,illustrate the law of constant composition.

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Answer 1

A chemical compound is always found tp be made up of the same elements combined together in the same fixed propotion by mass.
Discovered by J. proust

Step 1 :
Mass of lead proxide formed = 12.976 + 2.004g

14.980 g of lead proxide contain 2.004 g
of oxygen
hence 100 g of lead peroxide will contain
= 2.004 / 14.980 x 100 g

Oxygen present
= 13.38 %

Step 2 :
To compare the % of oxygen in both experiment .
% of oxygen in PbO2 in first Ex. = 13.38
% of oxygen in PbO2 in 2nd Ex. = 13.38

Since the percentage composition of oxygen in both the sample of PbO2 is identical , the above data illustrate the law of constant composition.

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