Calculate the Percentage of Nitrogen in an Organic Compound Using Kjeldahl Method
Introduction
Answer: 21%
The Kjeldahl method is a standard method used for the determination of nitrogen content in organic compounds. According to the problem statement, 0.3 g of the organic compound was Kjeldahlized and the ammonia evolved was absorbed into 45 mL of semi-normal sulfuric acid. The residual acid solution was diluted and 20 mL of this diluted solution required 31 mL of 0.05 N NaOH for complete neutralization. Let's first calculate the number of moles of NaOH used for the neutralization reaction: moles of NaOH = 0.05 N x 0.031 L = 0.00155 moles From the balanced chemical equation for the neutralization reaction between H2SO4 and NaOH, we know that 1 mole of NaOH reacts with 1 mole of H2SO4. Therefore, the number of moles of H2SO4 in the 20 mL of diluted solution used for titration is also 0.00155 moles. We know that the residual acid solution was diluted to 150 mL, so the total volume of the diluted solution is: 150 mL = 45 mL + volume of residual acid solution Therefore, the volume of the residual acid solution is: volume of residual acid solution = 150 mL - 45 mL = 105 mL Now, we can calculate the concentration of the residual acid solution in terms of normality: normality of residual acid solution = (0.5 N) x (45 mL / 105 mL) = 0.214 N The nitrogen content in the organic compound can be calculated using the following formula: % nitrogen = (molarity of H2SO4 x volume of H2SO4 x 14 x 100) / weight of organic compound where 14 is the atomic weight of nitrogen. We know the weight of the organic compound is 0.3 g, and we need to calculate the molarity of H2SO4 and the volume of H2SO4 used in the Kjeldahlization reaction. In the Kjeldahl method, nitrogen in the organic compound is converted to ammonium sulfate by reacting it with sulfuric acid. The reaction can be represented as follows: R-NH2 + 2H2SO4 + 2HgO → (NH4)2SO4 + 2Hg + 3H2O + 2SO4 Here, R represents the organic compound. From the balanced chemical equation, we know that 2 moles of H2SO4 are required to react with 1 mole of nitrogen. Therefore, the number of moles of H2SO4 used in the Kjeldahlization reaction is: moles of H2SO4 = (0.214 N) x (105 mL / 1000 mL) x 2 = 0.045 moles The volume of H2SO4 used in the Kjeldahlization reaction can be calculated using the molarity and the number of moles: volume of H2SO4 = moles of H2SO4 / molarity of H2SO4 = 0.045 moles / 0.5 N = 0.09 L Now we can calculate the percentage of nitrogen in the organic compound: % nitrogen = (0.5 N x 0.09 L x 14 x 100) / 0.3 g = 21% (approx.) Therefore, the percentage of nitrogen in the organic compound is approximately 21%.What is the Kjeldahl method used for?
The Kjeldahl method is a standard method used for the determination of nitrogen content in organic compounds.