Question

A compound A of S, Cl and O has a vapour density of \(67.5\). It reacts with water to form two acids and reacts with \(\mathrm{KOH}\) to form two salts \(\mathrm{B}\) and \(\mathrm{C}\). while B gives white precipitate with \(\mathrm{AgNO}_{3}\) solution, C gives white precipitate with \(\mathrm{BaCl}_{2}\) solution. Identify A (a) \(\mathrm{SOCl}_{2}\) (b) \(\mathrm{SO}_{2} \mathrm{Cl}_{2}\) (c) \(\mathrm{SO}_{2} \mathrm{Cl}\) (d) none of these

Short answer

The compound is \(\mathrm{SO_2Cl_2}\).

Step-by-step solution

Analyze the Problem

We need to identify a compound \(A\) based on its reactions and properties. The compound contains sulfur (S), chlorine (Cl), and oxygen (O) and has a vapor density of \(67.5\). The compound reacts with water to form two acids and with KOH to form two salts. These salts provide specific reactions with \(\mathrm{AgNO_3}\) and \(\mathrm{BaCl_2}\).

Calculate Molar Mass from Vapor Density

The vapor density is given as \(67.5\). Recall that vapor density is half the molar mass, so we calculate the molar mass as \(2 \times 67.5 = 135\). So, the molar mass of compound \(A\) should be approximately 135 g/mol.

Match Molar Mass with Options

Now, we need to check which of the given compounds has a molar mass of approximately 135. The compounds are:(a) \(\mathrm{SOCl_2}\) with molar mass = 32 (S) + 16 (O) + 2 \times 35.5 (Cl) = 119 g/mol.(b) \(\mathrm{SO_2Cl_2}\) with molar mass = 32 (S) + 2 \times 16 (O) + 2 \times 35.5 (Cl) = 135 g/mol.(c) \(\mathrm{SO_2Cl}\) with hypothetical molar mass, as it doesn't exist as a stable compound, but would be approximately 103 g/mol.The closest match for the molar mass of 135 g/mol is \(\mathrm{SO_2Cl_2}\) option (b).

Verify Reactions

Now we verify that \(\mathrm{SO_2Cl_2}\) fits the reaction scheme described. \(\mathrm{SO_2Cl_2}\) reacts with water to form \(\mathrm{HCl}\) and \(\mathrm{H_2SO_4}\), both acids. When reacted with KOH, it can form \(\mathrm{KCl}\) and \(\mathrm{K_2SO_4}\). \(\mathrm{KCl}\) can form a white precipitate \(\mathrm{AgCl}\) with \(\mathrm{AgNO_3}\), and \(\mathrm{K_2SO_4}\) forms a white precipitate \(\mathrm{BaSO_4}\) with \(\mathrm{BaCl_2}\), which matches the description.

Key concepts

Molar Mass Calculation

The concept of molar mass is crucial in chemistry because it allows us to understand the quantitative properties of substances. Molar mass represents the mass of one mole of a given substance, and it's generally expressed in grams per mole (g/mol). In this exercise, we are given the vapor density of the compound A as 67.5. To calculate the molar mass from this, remember that vapor density is half the molar mass of a compound.

To find the actual molar mass, we simply multiply the vapor density by 2. So we compute:\[\text{Molar Mass} = 2 \times 67.5 = 135 \, \text{g/mol}\]
With the molar mass known, we can proceed to compare the calculated molar mass with those of the given options to identify the most probable compound.

Reaction with Water

Reactions with water can help identify compounds due to the unique products they form. Compound A reacts with water to produce two acids: hydrochloric acid (HCl) and sulfuric acid (H2SO4). This means that the compound A contains elements that under hydrolysis will yield these acids.

In simpler terms, hydrolysis is a chemical reaction involving water that breaks down a compound. For compound A, the reaction can be seen as:\[\text{SO}_2\text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{H}_2\text{SO}_4\]
This reaction is pivotal because the formation of these specific acids points to SO2Cl2 as the compound.

Precipitation Reaction

Precipitation reactions are valuable for identifying substances because they result in the formation of a solid, or precipitate, when two aqueous solutions are combined. Here, compound A reacts with KOH to form salts B (KCl) and C (K2SO4). Both of these salts further undergo precipitation reactions with different reagents.

When the salt KCl (B) is combined with AgNO3, it forms a white precipitate known as silver chloride (AgCl). For the salt K2SO4 (C), it reacts with BaCl2 forming barium sulfate (BaSO4), which is also a white precipitate.

• Reaction with AgNO3: \[\text{KCl} + \text{AgNO}_3 \rightarrow \text{AgCl}\, (\text{white precipitate}) + \text{KNO}_3\]
• Reaction with BaCl2:\[\text{K}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4\, (\text{white precipitate}) + 2\text{KCl}\]

This series of reactions helps confirm the identity of compound A based on the specific precipitates formed.

Identification of Compound

The process of identifying a compound involves matching its properties and reactions with known chemical behaviors. In this case, compound A is characterized by its vapor density, reactions with water, and formation of specific salts. After determining the molar mass to be 135 g/mol, option (b), SO2Cl2, fits this calculation.

Moreover, SO2Cl2's reaction to form HCl and H2SO4 with water, as well as forming specific white precipitates with AgNO3 and BaCl2, aligns perfectly with the observations in the exercise. These factors together lead us to establish SO2Cl2 as compound A. Thus, the identification is complete based on a holistic view of the chemical data and reactions provided in the problem description.