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Step-by-Step Solution
Step 1: Understand the Kjeldahl Method Setup
In Kjeldahl’s method for nitrogen estimation, the organic compound is digested in the presence of concentrated sulfuric acid and a catalyst. The nitrogen in the organic compound is converted into ammonium sulfate in the acidic solution. When this solution is then treated with a base, ammonia (NH3) is liberated and absorbed in a known amount of acid. Any remaining or unreacted acid is then titrated with a standard solution of a base (e.g., NaOH).
Step 2: Identify the Given Data
Mass of organic compound = 1.4 g
Volume of M/10 (0.1 M) H2SO4 used = 60 mL
Volume of M/10 (0.1 M) NaOH used to neutralize the leftover acid = 20 mL
Step 3: Calculate the Milliequivalents (meq) of Acid and Base
The milliequivalents of an acid or base can be calculated as:
$ \text{meq} = \text{Volume in mL} \times \text{Normality} $
Since M/10 H2SO4 is 0.1 M and sulfuric acid provides 2 equivalents of H+ per mole, its normality is 0.2 N (because Normality for H2SO4 = Molarity × 2). Thus:
$ \text{meq of } H_2SO_4 = 60 \times 0.2 = 12 $
Similarly, for M/10 (0.1 M) NaOH, the normality is 0.1 N (since NaOH provides 1 equivalent of OH− per mole):
$ \text{meq of NaOH} = 20 \times 0.1 = 2 $
Step 4: Determine the Effective meq of Acid Used to Absorb Ammonia
Out of the initial 12 meq of H2SO4, 2 meq remain unneutralized by ammonia and are instead neutralized by NaOH. Therefore, the actual meq of acid consumed by the liberated ammonia is:
$ \text{meq of acid consumed by NH}_3 = 12 - 2 = 10 $
Step 5: Calculate the Percentage of Nitrogen
In the Kjeldahl method, each meq of acid consumed corresponds to the amount of ammonia produced from the nitrogen in the organic compound. Using the given data:
$ \% \ N = \frac{\text{(Mass of compound) } \times \text{(meq of acid consumed)}}{\text{(Mass of compound)}} $
Here, because the factor used is directly based on the meq of acid neutralized by NH3, the numeric calculation simplifies as follows:
$ \% \ N = \frac{(1.4 \times 10)}{1.4} = 10\% $
Final Answer
The percentage of nitrogen ($N$) in the given organic compound is 10%.
