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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.

^_Element	^_Percentage	^{_{Atomic Mass}}	^{_{Atomic ration}}	^{_{Simplest ratio}}	^{_{Simplest whole number ratio}}
^{_{Iron (Fe)}}	^_69.9	^_55.85	^{_{69.9/55.85=1.25}}	^{_{1.25/1.25 =1}}	^₂
^{_{Oxygen (O)}}	^_30.1	^_16.00	^{_{30.1/16.00=1.88}}	^{_{1.88/1.25=1.5}}	^₃

Empirical formula Fe2O3

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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.

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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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160.

A sample of hydrazine consists of 87·42% N and 12·58% H by mass. The molecular mass of hydrazine is 32·0 g mol^–1. Calculate its molecular formula.

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