Question

A solution of a compound \(X\) in dilute \(\mathrm{HCl}\) on treatment with a solution of \(\mathrm{BaCl}_{2}\) gives a white precipitate of a compound \(Y\) which is insoluble in coac. \(\mathrm{HNO}_{3}\) and conc. \(\mathrm{HCl}\). Compound \(X\) imparts golden yellow colour to the flame. yellow colour) What are compounds \(X\) and \(Y ?\) (a) \(X\) is \(\mathrm{MgCl}_{2}\) and \(Y\) is \(\mathrm{BaSO}_{4}\)(b) \(X\) is \(\mathrm{CaCl}_{2}\) and \(Y\) is \(\mathrm{BaSO}_{4}\) (c) \(X\) is \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) and \(Y\) is \(\mathrm{BaSO}_{4}\) (d) \(X\) is \(\mathrm{MgSO}_{4}\) and \(Y\) is \(\mathrm{BaSO}_{4}\)

Short answer

Compound X is Na2SO4 and compound Y is BaSO4.

Step-by-step solution

Analyze the Chemical Reaction

Consider the given information: a compound X in dilute HCl when reacted with BaCl2 forms a white precipitate Y, which is insoluble in concentrated HNO3 and concentrated HCl. This suggests that the precipitate Y is likely to be an insoluble sulfate, as BaSO4 is known to have such properties.

Identify the Precipitate Y

Given the information that the precipitate is insoluble in concentrated HNO3 and concentrated HCl, it's reasonable to conclude that the precipitate Y is BaSO4, because BaSO4 is known to be insoluble in these solvents. A reaction between a sulfate and BaCl2 would result in the formation of BaSO4.

Determine the Flame Color of Compound X

The compound X imparts a golden yellow color to the flame, which is characteristic of sodium ions. The presence of sodium ions suggests that compound X must contain sodium, and since Y is BaSO4, X must be a sodium sulfate compound.

Identify Compound X

Matching the known properties of compound X, the flame colour, and the formation of a white precipitate with BaCl2, we confirm that compound X is a sodium sulfate. Therefore, compound X is Na2SO4.

Key concepts

Precipitation Reaction

Understanding chemical reactions is fundamental in chemistry, and one of the types of reactions that we often encounter is the precipitation reaction. This reaction occurs when two soluble reactants combine to form an insoluble product, called a precipitate. For example, when a solution of compound X (a sulfate) reacts with barium chloride (BaCl_2), a white precipitate of compound Y is formed. This is a classic precipitation reaction, where the product, compound Y, precipitates out of the solution because it is no longer soluble.

Precipitation reactions are not only fascinating from a scientific perspective but are also utilized in a variety of practical applications such as water treatment, where harmful ions are removed through precipitation. One key aspect of understanding these reactions is recognizing the solubility rules, which help predict the formation of a precipitate. In the textbook solution, the white precipitate Y being insoluble in both concentrated nitric acid (HNO_3) and hydrochloric acid (HCl) leads to the conclusion that Y is likely barium sulfate (BaSO_4), which aligns with known solubility properties of sulfates.

Flame Test

The flame test is a simple yet powerful analytical technique used in chemistry to detect the presence of certain metal ions based on the color they impart to a flame. During the test, a sample of a compound is introduced to a flame, and the characteristic color emitted is observed. This happens due to the excitation of electrons within the metal ion, which then emit specific wavelengths of light upon returning to their ground state.

The golden yellow flame mentioned in the textbook exercise is a classic indication of sodium ions (Na^+). Each metal ion has a unique electron arrangement, which results in a unique flame color when excited. For instance, copper typically yields a green or blue flame, while potassium produces a violet flame. Recognizing these colors is essential for identifying unknown samples. In the context of the textbook exercise, the golden yellow flame color allows us to conclude that compound X contains sodium ions, leading us to identify X as sodium sulfate (Na_2SO4).

Solubility Properties

The concept of solubility properties is crucial when discussing chemical reactions, particularly precipitation reactions. Solubility refers to the ability of a substance to dissolve in a solvent, forming a homogeneous solution. It is determined by factors such as temperature, pressure, and the chemical nature of the solute and solvent.

In the context of the exercise, understanding the solubility rules allows us to decipher that barium sulfate (BaSO_4) is insoluble in water and common acidic solutions. This kind of knowledge is critical when predicting whether a chemical reaction will result in a precipitate or not. For example, silver chloride is insoluble in water but will dissolve in ammonia, while most sodium compounds, including sodium sulfate (Na_2SO4), are soluble in water. Thus, the correct identification of compound Y as barium sulfate points to its characteristic insolubility, which informs us that X must be a compound that contains sulfate ions in a soluble form (such as sodium sulfate).