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Chemistry

(i) Define : Relative atomic mass.

(ii) Why is it necessary to balance a chemical equation ?

(iii) Calculate the percentage of nitrogen in ammonium phosphide. (At.wt. : N = 14, P = 31, O = 16)

Relative Atomic Mass

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Answer

(i) The number of times one atom of an element is heavier than 112\dfrac{1}{12}th the mass of an atom of carbon [C12] is known as the Relative Atomic Mass [RAM] of the element.

(ii) An equation must be balanced in order to comply with the "Law of Conservation of Matter", which states that matter is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

(iii) Molar mass of ammonium phosphide [(NH4)3PO4]

= 3[14 + 4(1)] + 31 + 4(16)]

= 3[18] + 31 + 64

= 54 + 31 + 64

= 149 g

Mass of nitrogen in one mole of ammonium phosphide = 3 x 14 = 42 g

149 g of ammonium phosphide contains 42 g of nitrogen.

∴ 100 g of ammonium phosphide contains 42×100149\dfrac{42 \times 100 }{149} = 28.18% of nitrogen.

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