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Some Basic Concepts of Chemistry

Long Answer Type

151. Fe₂(SO₄)₃ is the empirical formula of a crystalline compound of iron. It is used in water and sewage treatment for the removal of suspended impurities. Calculate the mass percentage of iron, sulphur and oxygen in the compound.

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Short Answer Type

152.

What is the empirical formula of the compounds having molecular formula as:
(i) C₆H₆
(ii) C₆H₁₂(iii) H₂O₂
(iv) H₂O
(v) Na₂CO₃(vi) B₂H₆(vii) N₂O₆

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153. Determine the empirical formula of an oxide of iron which has 69·9% iron and 30.1% dioxygen by mass.

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Long Answer Type

154.
Silicon (Si = 28) forms a compound with chlorine (Cl = 35·5) in which 5·6g of silicon is combined with 21·3g of chlorine. Calculate the empirical formula of the compound.

(i) To calculate the percentage of silicon and chlorine:
Weight of silicon = 5.6 g
Weight of chlorine = 21.3 g

(ii) To calculate the empirical formula:

Element	%	atomic no.	atomic ratio	simplest ratio	simple whole ratio
Silicon	20.8	28	20.8/28=0.74	0.74/0.74=1	1
Chlorine	79.2	35.5	79.2/35.5=2.23	2.23/0.74=3	3

Therefore empirical formula is SiCl₃.

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155.

2.38 g of uranium was heated strongly in a current of air. The resulting oxide weighed 2806 g. Determine the empirical formula of the oxide. (At. mass of U = 238, O = 16).

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156.

Four grams of copper chloride on analysis was found to contain 1·890 g of copper (Cu) and 2·110 g of chlorine (Cl). What is the empirical formula of copper chloride?

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157. The atomic mass of metal M is 56. Calculate the empirical formula of its oxide containing 70% of M.

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158. A chemical compound is found to have the following composition: C = 19·5%, Fe = 15·2%, N = 22·8%, K = 41·5%. Calculate the empirical formula of the compound. What will be the molecular formula if the molecular mass of the compound is 368? Name the compound also.

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159.

A compound on analysis, is found to have the following composition:
(i) Sodium = 14·31%, (ii) Sulphur = 9·97
(iii) Oxygen = 69·50% (iv) Hydrogen = 6·22%.
Calculate the molecular formula of the compound assuming that whole of hydrogen in the compound is present as water of crystallisation. Molecular weight of the compound is 322.

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