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Model Paper 10 — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 105 Marks
Question
1. Suggest a method to purify
i. a liquid which decomposes at its boiling point.
ii. kerosene oil containing water.
iii. camphor containing traces of common salt.
2. Differentiate between the principle of estimation of nitrogen in an organic compound
i. Dumas method
ii. Kjeldahl's method.
✓

Answer

(1). i. Distillation under reduced pressure.
ii. Since the two liquids are immiscible, the technique of solvent extraction with a separating funnel is used. Kerosene being lighter than water forms the upper layer while water forms the lower layer. The lower water layer is run off when kerosene oil is obtained. It is dried over anhydrous $CaCl _2$ or $M _{ g } SO _4$ and then distilled to give pure kerosene oil.
iii. Sublimation Camphor sublimes while common salt remains as residue in the China dish.
(2). (i) Dumas method: The organic compound is heated strongly with excess of CuO (Cupric oxide) in an atmosphere of $CO _2$ when free nitrogen, $CO _2$ and $H _2 O$ are obtained.
(ii) Kjeldahl's method: A known mass of the organic compound is heated strongly with conc. $H _2 SO _4$ and a little potassium sulphate and a little mercury (a catalyst). As a result of reaction the nitrogen present in the organic compound is converted to ammonium sulphate.

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