Problem 29 - Chemistry in 30 days

Question

The ammonia evolved from the treatment of \(0.30 \mathrm{~g}\) of an organic compound ror the estimation of nitrogen was passed in \(100 \mathrm{~mL}\) of \(0.1 \mathrm{M}\) sulphuric acid. The excess of acid required \(20 \mathrm{~mL}\) of \(0.5 \mathrm{M}\) sodium hydroxide solution for complete neutralization. The organic compound is (a) urea (b) thiourea (c) acetamide (d) benzamide

Step-by-Step Solution

Answer

The organic compound is (a) urea.

Step 1: Understand the Problem

We have an organic compound whose nitrogen content is estimated by reacting it to release ammonia, which is absorbed by a known quantity of excess sulphuric acid. The excess acid is then neutralized by sodium hydroxide. We'll use this data to determine which compound from the given list matches the calculations.

Step 2: Write Down the Reaction Involved

The ammonia reacts with sulphuric acid as follows:\[\text{2 NH}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{(NH}_4\text{)}_2\text{SO}_4\]We initially use 100 mL of 0.1 M sulphuric acid, hence introducing 0.01 moles of sulphuric acid.

Step 3: Calculate Moles of Excess Acid Neutrlaized

Excess sulphuric acid is neutralized by 20 mL of 0.5 M sodium hydroxide:\[\text{Volume of NaOH} = 20 \text{ mL} = 0.020 \text{ L}\]\[\text{Moles of NaOH} = 0.020 \times 0.5 = 0.01 \text{ moles}\]Since each mole of sulphuric acid reacts with two moles of sodium hydroxide, the moles of excess acid are \[0.01 / 2 = 0.005\].

Step 4: Calculate Moles of Acid Reacted with Ammonia

Total moles of sulphuric acid added = 0.01 molesMoles of excess acid = 0.005 molesThus, moles of acid reacted with ammonia = \[0.01 - 0.005 = 0.005\] moles.

Step 5: Calculate Moles of Nitrogen in the Compound

Since 1 mole of sulphuric acid reacts with 2 moles of ammonia, it follows that the moles of ammonia (and therefore nitrogen) is \[0.005 \times 2 = 0.01\] moles. Since each mole of nitrogen corresponds to 14 g/mol, we find:\[\text{Mass of nitrogen} = 0.01 \times 14 = 0.14 \text{ g}\].

Step 6: Identify the Compound

We have 0.14 g of nitrogen in 0.30 g of compound. Calculate the nitrogen percentage:\[\text{Percentage of nitrogen} = \left( \frac{0.14}{0.30} \right) \times 100 \approx 46.67\%\].Comparing this with the list of compounds, we find that urea (option a) has the closest nitrogen percentage.

Key Concepts

Ammonia Evolution Method

The Ammonia Evolution Method is an effective and commonly used approach for determining the nitrogen content in organic compounds. This technique involves treating an organic compound to release ammonia gas. The ammonia produced is collected in a known excess amount of sulfuric acid, which reacts with the ammonia to form ammonium sulfate. This method is beneficial because it allows for a complete recovery of nitrogen in the sample as ammonia, making it highly reliable for quantitative analysis.
The process consists of several key steps:

• Decomposition of the organic compound to release ammonia.
• Absorption of ammonia in an acidic solution, usually involving sulfuric acid.
• Neutralizing any excess acid with a base, such as sodium hydroxide, to determine how much acid reacted with the ammonia.

The accuracy of this method depends on ensuring that all the evolved ammonia is completely absorbed by the acid.

Organic Compound Analysis

Organic Compound Analysis involves examining organic substances to ascertain their chemical composition. A central aspect of this analysis is the determination of nitrogen content, especially when dealing with compounds that incorporate nitrogen in their chemical structure. Such analytical studies are critical in various fields like biochemistry, pharmacology, and industrial chemistry.
The process begins with the sample preparation, where the compound is finely powdered. Following this, specific reactions, like the ammonia evolution method, are employed to release nitrogen-containing gases for further analysis. Determining the nitrogen content helps in identifying the possible molecular structure and characteristics of the compound. This analysis is important for applications ranging from quality control to the synthesis of new chemical entities.

Nitrogen Content in Compounds

Knowing the Nitrogen Content in Compounds is vital, particularly in fields that involve pharmaceuticals, agriculture, and chemistry. Nitrogen is an integral part of many biological molecules, such as amino acids and nucleotides.
The percentage of nitrogen in a compound is calculated by measuring the amount of nitrogen gas evolved in reactions, usually involving the conversion to ammonia. The weight of nitrogen can then be proportionally compared to the total mass of the compound to determine its percentage. For example, if a certain compound releases a precise amount of nitrogen, and the compound's total mass is known, the nitrogen percentage can be easily computed.
Determining nitrogen content helps in concluding the suitability of the compound for its intended application, ensuring that the exact specifications adhere to what's required for its use.

Neutralization Reactions

Neutralization Reactions are chemical reactions in which an acid and a base react quantitatively with each other. During this process, they produce a salt and water as the primary products. In the context of determining nitrogen content by ammonia evolution, neutralization is used to measure the amount of unreacted sulfuric acid after it has captured the evolved ammonia.
In these reactions, the precise concentration and volume of acid and base solutions are critical for accurate results. For instance, if 0.5 M sodium hydroxide is used to titrate the leftover sulfuric acid in a solution, the amount of sodium hydroxide used can help determine how much sulfuric acid reacted with ammonia. This calculation is fundamental for measuring nitrogen content in the given compound.

Chemical Calculations

Chemical Calculations form the backbone of quantitative chemical analysis, allowing us to measure and interpret experiment results precisely. In the nitrogen estimation problem, several calculations are necessary to interpret the data correctly:

• Calculating the moles of sulfuric acid initially present, using its concentration and volume.
• Subtracting the moles neutralized with sodium hydroxide to find the moles of acid that reacted with ammonia, which corresponds to the moles of nitrogen released.
• Using the relationship between the moles of nitrogen and its molar mass to find the actual mass of nitrogen present in the compound.
• Finally, determining the percentage of nitrogen by comparing the nitrogen mass to the total mass of the compound.

These calculations are straightforward, but attention to detail is critical. Errors in any step can lead to inaccurate conclusions about the compound's nitrogen content.