Question

# 29.5 mg of an organic compound containing nitrogen was digested according to Kjeldahl's method and the evolved ammonia was absorbed in 20 mL of 0.1M HCl solution. The excess of the acid required 15 mL of 0.1 M NaOH solution for complete neutralization. The percentage of nitrogen in the compound is

A

$59.0$

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B

$47.4$

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C

$23.7$

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D

$29.5$

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Solution

## The correct option is C $23.7$Explanation for correct answer:-Option (C) $23.7$Step 1: Given data Volume of $\mathrm{HCl}=20\mathrm{ml}$Volume of $\mathrm{NaOH}=15\mathrm{ml}$ Step 2: Formula used : Moles of $\mathrm{HCl}$ reacting with ammonia = $\left(molesofHClabsorbed\right)–\left(molesofNaOHsolutionrequired\right)$ ---------------------(1)Step 3: Calculation of Moles of $\mathrm{HCl}$From eq (1) = $\left(20x0.1x{10}^{-3}\right)–\left(15x0.1x{10}^{-3}\right)$This will be equal to Moles of${\mathrm{NH}}_{3}$evolved which in turn gives moles of nitrogen in an organic compound.Step 4: Calculating the weight of Nitrogen Hence,Weight of nitrogen in organic compound = $0.5x{10}^{-3}x14$.We get,$=7x{10}^{-3}g$.Step 5:Deriving Percentage of nitrogenPercentage of nitrogen = $\left(7x{10}^{-3}\right)/\left(29.5x{10}^{-3}\right)x100$ $=23.7%$Therefore, the percentage of nitrogen in the compound is$23.7%$So, the correct option is (C).

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