 # The Law of Definite Proportion or Constant Composition  Written by

Law of Chemical Combination

Einstein derived an expression to the inter conservation of matter and energy given by E= mc2, where c is the velocity of light, E is energy and M is the mass.

The theory has now been put in the form of a law called the law of conservation of mass or law or law of indestructibility of matter

Law of conservation of mass state that matter can neither be created nor destroyed in the course of any chemical reaction.

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The Law of Definite Proportion or Constant Composition

The Law of Definite Proportion or Constant Composition state that all pure samples of the same chemical compound contain the same elements combined in the same proportion by mass.

The Law of Multiple Proportion

The law of multiple proportion state that if two element A and B are combined together to form more than one compound, the several masses of A which is separately combined with a fix masses of B are in the same sample ratio. Law of Chemical Combination

Some given solution to some test questions

1. What is the amount (in mole) of sodium trioxocarbonate (iv) in 5.3g of the compound? ( Na2Co3 = 106g)

B. 010

C. 0.20

D. 0.50

Solution

Mole = Reacting Mass/molar mass

Mole = 5.3/106 = 0.05mole

2. In two separate experiments, 0.36 and 0.71g of chlorine combined with a metal X to give Y and Z respectively. An analysis showed that Y and Z contain 0.20g and 0.40g of respectively. The data above represents the law of

B. conservation of mass

C. constant proportion

D. reciprocal proportion

3. Calculate the percentage composition of water of crystalization in the compound below? Sodium trioxocarbonate (iv) decahydrate i.e Na2CO3.10H20

B. 88.43%

C. 55.67%

D. 70.16%

Solution

Compound Na2CO3.10H20

2 x 23 + 1 x 12 + 3 x 16 + [20 x 1 + 10 x 16]

46 + 12 + 48 + 20 + 160 = 286g

[20 x 1 + 10 x 16] water of crystallization is 180

Then 180/286 x 100 = 62.94%

Try this and solve

6g of metal M reacts completely with 23.66g of chlorine to form 29.66g of the metallic chloride.find the emperical formula of the metallic chloride. ( M=27, Cl=35.5) • Trinidad Norfolk says: