Question

Hydrogen sulphide reacts with lead acetate forming a black compound which reacts with \(\mathrm{H}_{2} \mathrm{O}_{2}\) to form another compound. The colour of the compound is (a) Black (b) Yellow (c) White (d) Pink

Short answer

The compound is white (Option c).

Step-by-step solution

Identify reactions in the problem

The exercise describes a two-step reaction process. First, hydrogen sulphide (\(\text{H}_2\text{S}\)) reacts with lead acetate (\((\text{Pb(CH}_3\text{COO})_2)\)) to form a black compound, lead sulphide (\(\text{PbS}\)). This is the first reaction.

Analyze the further reaction with Hydrogen Peroxide

In the second step, the black lead sulphide (\(\text{PbS}\)) formed reacts with hydrogen peroxide (\(\text{H}_2\text{O}_2\)). This reaction typically converts lead sulphide into lead sulphate (\(\text{PbSO}_4\)) or lead oxide (\(\text{PbO}_2\)), both of which can be white in color.

Determine the color of the product

The compound formed after the reaction of lead sulphide with hydrogen peroxide is lead sulphate (\(\text{PbSO}_4\)), which is white. Therefore, the color we are looking for is white.

Key concepts

Hydrogen Sulphide

Hydrogen sulphide, denoted chemically as \( ext{H}_2 ext{S}\), is a colorless gas known for its pungent smell, reminiscent of rotten eggs. This characteristic odor makes it easy to identify in a laboratory setting. It is a simple molecule comprised of two hydrogen atoms bonded to a single sulfur atom, giving it a bent shape similar to water. Hydrogen sulphide is commonly found in natural gas and crude petroleum; it is also a byproduct of the decay of organic matter. It acts as a reducing agent in many chemical reactions due to its ability to donate electrons. This property makes it reactive with various metal ions, leading to the formation of new compounds.Safety is paramount when handling \( ext{H}_2 ext{S}\) because it is highly toxic even in low concentrations. Adequate ventilation and protective equipment are necessary when dealing with this gas to prevent harmful exposure.

Lead Acetate

Lead acetate is a chemical compound with the formula \( ext{Pb(CH}_3 ext{COO})_2\). Often known as sugar of lead due to its sweet taste, it appears as a white crystalline substance in its solid state but should never be tasted due to its toxicity. It is soluble in water, which makes it useful in various aqueous reactions. In the context of chemical reactions, lead acetate reacts readily with sulfide ions to precipitate lead sulfide, an insoluble black solid. This property is useful in qualitative analysis for the detection of sulfide ions. Additionally, lead acetate was once used in hair dye products and as a drying agent, although these uses have decreased due to safety concerns. Lead acetate is toxic and can lead to lead poisoning if ingested or improperly handled, necessitating safe handling procedures in laboratories and industrial settings.

Lead Sulphide

Lead sulphide (\( ext{PbS}\)) is an important compound in both industrial and chemical settings. It appears as a black solid and is a principal ore of lead and a significant material in making lead-based products. This compound is formed when hydrogen sulphide gas reacts with solutions containing lead ions, such as lead acetate. The reaction occurs when the sulfide ions from hydrogen sulphide combine with lead to produce the insoluble black solid. Lead sulphide possesses unique optical and electrical properties, making it valuable in the manufacturing of infrared detectors and other semiconductor applications. The black color of lead sulfide is often used for historical blackening processes, marking it a multifunctional compound in both practical and aesthetic contexts.

Lead Sulphate

Lead sulphate, denoted as \( ext{PbSO}_4\), is a white solid that forms when lead sulphide reacts with hydrogen peroxide. This chemical transformation occurs through an oxidation reaction where the lead sulphide is converted into lead sulphate in the presence of an oxidizing agent like \( ext{H}_2 ext{O}_2\). Lead sulphate is insoluble in water, which distinguishes it from many other common sulfates. Due to its insolubility, it is often encountered as a solid precipitate. In industrial applications, lead sulphate is used in lead-acid batteries and sometimes in the coloring of ceramics.The formation of lead sulphate is an example of how chemical reactivity can alter the properties and color of a compound, transforming black lead sulfide into a white compound, showcasing the versatility and complexity of chemical reactions.