### Law of constant proportion

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Law of constant proportion or definite composition-

This law was stated by Louis Proust. According to this law,

‘ A pure chemical compound always contains same elements combined together in the same definite proportion by mass.’

#### Experimental Verification-

Carbon dioxide can be obtained by so many methods like,

(i) By respiration ( as byproduct )

(ii) By burning coal-

C + O2 ——> CO2

(iii) By heating lime stone-

CaCO3 ———> CaO + CO2

(iv) By heating Sodium bicarbonate-

2NaHCO3 ——>Na2CO3 +H2O + CO2

(v) By the reaction of Dilute Hydrochloric acid & Calcium  carbonate-

2CaCO3 + 2HCl ——–> CaCl2 + H2O + CO2

### problem 1)

#### Solution-

Cu           +      HNO3    ——–>     Cu(NO3)2      ———–> CuO

1.08 gram                                                                                      1.35 gram

a)  1.35 gram  CuO contains Cu = 1.08 gram

100 gram CuO contains Cu = 1.08 X100/1.35 =80 gram

% of Cu in CuO =80%

% of O in CuO =(100-80) =20%

b) CuO      +      H2 ——>   Cu         +     H2O

2.3 gram                          1.84 gram

2.3 gram  CuO contains Cu = 1.84 gram

100 gram CuO contains Cu = 1.84 X100/2.3 =80 gram

% of Cu in CuO =80%

% of O in CuO =(100-80) =20%

### Solution –

i)  CuO        +       H2 —–> Cu             +       H2O

1.375 gram                      1.098 gram

1.375  gram  CuO contains Cu = 1.098 gram

100 gram CuO contains Cu = 1.098 X100/1.375 = 79.8 gram = 80 gram

% of Cu in CuO =80%

ii)   Cu           +      HNO3    ——–>     Cu(NO3)2      ———–> CuO

1.178 gram                                                                                      1.476 gram

1.476 gram  CuO contains Cu = 1.178 gram

100 gram CuO contains Cu = 1.178 X100/1.476 = 79.8 = 80 gram

% of Cu in CuO =80%

% of O in CuO =(100-80) =20%

% of Cu in both the cases is same .So data follows law of constant proportion.

### Solution-

100 gram crystalline copper sulphate ( CuSO4.5H2O) contains Cu = 25.45 gram

40 gram crystalline copper sulphate ( CuSO4.5H2O) contains Cu = 25.45 X 40 /100=10.18 gram Ans.