Question 27 of 34intermediate🔧 ApplyNumerical3 marks

A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 ml of 0.5 M H₂SO₄. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.

Correct Answer

56%

Exercise: EXERCISES | Q: 8.33
For More Understanding

Explanation

To find the percentage of nitrogen using Kjeldahl's method, we calculate the volume of acid that reacted with the evolved ammonia. The total acid taken is reduced by the acid neutralised by the residual NaOH. The formula relates the mass of nitrogen to the volume of acid reacted, and finally gives the percentage composition based on the mass of the organic compound taken.

Solution Steps

  1. Step 1: Identify the given values from the question: Mass of organic compound (mm) = 0.50 g, Molarity of H2SO4H_2SO_4 and NaOHNaOH (MM) = 0.5 M, Volume of H2SO4H_2SO_4 taken (VV) = 50 mL, Volume of NaOHNaOH used for neutralisation (V1V_1) = 60 mL.

  2. Step 2: Apply the formula for the percentage of nitrogen from Kjeldahl's method: Percentage of N = 1.4×M×2(V−V1/2)m\frac{1.4 \times M \times 2(V - V_1 / 2)}{m}

  3. Step 3: Substitute the given values into the formula: Percentage of N = 1.4×0.5×2(50−60/2)0.50\frac{1.4 \times 0.5 \times 2(50 - 60 / 2)}{0.50}

  4. Step 4: Solve the expression: Percentage of N = 1.4×0.5×2(50−30)0.50=1.4×0.5×400.50=280.50=56%\frac{1.4 \times 0.5 \times 2(50 - 30)}{0.50} = \frac{1.4 \times 0.5 \times 40}{0.50} = \frac{28}{0.50} = 56\%

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