**Law of Chemical Combination**

Einstein derived an expression to the inter conservation of matter and energy given by **E= mc ^{2}, **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.

**Some given solution to some test questions **

1. What is the amount (in mole) of sodium trioxocarbonate (iv) in 5.3g of the compound? ( Na_{2}Co_{3 }= 106g)

A.0.05 **Answer**

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

A. Multiple proportion **Answer**

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 Na_{2}CO_{3}.10H_{2}0

A. 62.94% **Answer**

B. 88.43%

C. 55.67%

D. 70.16%

**Solution **

Compound Na_{2}CO_{3}.10H_{2}0

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)

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