**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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### Experiment To Verify The Law Of Conservation Of Mass

Reagents: Silver trioxonitrate (v) solution and potassium chloride solution and potassium chloride solution

Method

Put some potassium chloride solution in a conical flask. Fill a small test tube with trioxonitrate (v) solution and by means of a string, let the test tube be suspended in the conical flask, cover the flask with a stopper and weigh.

The lift the conical flask and shake to allow to mix together. After mixing, a white precipitate of silver chloride is formed and a colourless solution of potassium trioxonitrate (v).

**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.

Another name for Definite proportion is constant composition.

**The Law of Multiple Proportion**

Dalton’s fourth Theory is that chemical combinations take place between small whole number ratio atoms.

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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