Problem 151 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following $$ \begin{array}{ll} \hline \text { List-I } & \text { List-II } \\ \hline \text { a. } \mathrm{AgNO}_{3}+\mathrm{NaCNS} & \text { (p) White } \\ \text { b. } \mathrm{AgNO}_{3}+\mathrm{Na}_{3} \mathrm{PO}_{4} & \text { (q) Black } \\ \text { c. } \mathrm{AgNO}_{3}+\mathrm{K}_{2} \mathrm{CrO}_{4} & \text { (r) Brick red } \\ \text { d. } \mathrm{AgNO}_{3}+\mathrm{Na}_{2} \mathrm{~S} & \text { (s) Yellow } \\ \hline \end{array} $$

Step-by-Step Solution

Answer

a - (p) White, b - (s) Yellow, c - (r) Brick red, d - (q) Black.

Step 1: Reaction of Silver Nitrate with Sodium Thiocyanate

When \( \mathrm{AgNO}_{3} \) is reacted with \( \mathrm{NaCNS} \), the product formed is \( \mathrm{AgCNS} \), which is white in color. Therefore, the match for 'a' is (p) White.

Step 2: Reaction of Silver Nitrate with Trisodium Phosphate

In the reaction between \( \mathrm{AgNO}_{3} \) and \( \mathrm{Na}_{3} \mathrm{PO}_{4} \), \( \mathrm{Ag}_{3}\mathrm{PO}_{4} \) is formed, which is yellow in color. Thus, 'b' matches with (s) Yellow.

Step 3: Reaction of Silver Nitrate with Potassium Chromate

\( \mathrm{AgNO}_{3} \) reacting with \( \mathrm{K}_{2} \mathrm{CrO}_{4} \) produces \( \mathrm{Ag}_{2}\mathrm{CrO}_{4} \), which appears as a brick red solid. Thus, 'c' pairs with (r) Brick red.

Step 4: Reaction of Silver Nitrate with Sodium Sulfide

The reaction between \( \mathrm{AgNO}_{3} \) and \( \mathrm{Na}_{2} \mathrm{S} \) forms \( \mathrm{Ag}_{2}\mathrm{S} \), which is black in color. Therefore, 'd' corresponds to (q) Black.

Key Concepts

Silver Nitrate Reactions

Silver nitrate, represented as \( \mathrm{AgNO}_{3} \), is a highly versatile chemical in the field of inorganic chemistry. When it interacts with different compounds, it gives rise to a variety of reactions, often forming precipitates with distinct colors.

One well-known reaction involves mixing silver nitrate with sodium thiocyanate \( \mathrm{NaCNS} \). This results in the formation of silver thiocyanate \( \mathrm{AgCNS} \), which is known for its white precipitate. Similarly, when silver nitrate meets trisodium phosphate \( \mathrm{Na}_{3} \mathrm{PO}_{4} \), it yields silver phosphate \( \mathrm{Ag}_{3}\mathrm{PO}_{4} \), creating a yellow precipitate.

Silver nitrate also reacts with potassium chromate \( \mathrm{K}_{2} \mathrm{CrO}_{4} \), forming silver chromate \( \mathrm{Ag}_{2} \mathrm{CrO}_{4} \), which is characterized by its brick red precipitate. Lastly, when silver nitrate combines with sodium sulfide \( \mathrm{Na}_{2} \mathrm{S} \), silver sulfide \( \mathrm{Ag}_{2} \mathrm{S} \) is produced, yielding a black precipitate.

Precipitate Colors in Chemistry

Understanding the colors of precipitates in chemical reactions can be essential for students learning about reaction types and compound identification. In the realm of silver compounds, these colors can be quite distinctive.

The color of a precipitate can often provide crucial information regarding the compounds involved in the reaction. For instance, a white precipitate when reacting silver nitrate can suggest the formation of silver thiocyanate \( \mathrm{AgCNS} \). If you observe a yellow precipitate, it is likely silver phosphate \( \mathrm{Ag}_{3}\mathrm{PO}_{4} \).

• Brick Red: Typically associated with silver chromate \( \mathrm{Ag}_{2} \mathrm{CrO}_{4} \)
• Black: Commonly denotes the presence of silver sulfide \( \mathrm{Ag}_{2} \mathrm{S} \)

Recognizing these colors and their relation to specific compounds not only helps in identifying reactions but also in better appreciating the variety and beauty of chemistry.

Silver Compound Formation

When it comes to silver compounds, their formation and characteristics are a fascinating study area in chemistry. Each compound reflects different properties, primarily dictated by the elements they are combined with.

Silver nitrate, a key reagent in these reactions, often leads to the creation of various silver-containing compounds, each with distinct physical properties. For example, silver thiocyanate \( \mathrm{AgCNS} \) precipitates as white, while silver phosphate \( \mathrm{Ag}_{3}\mathrm{PO}_{4} \) emerges as yellow.

The formation of silver chromate \( \mathrm{Ag}_{2} \mathrm{CrO}_{4} \) is another classic example, known for its brick red appearance. This is due to the specific arrangement of atoms within the compound. Meanwhile, silver sulfide \( \mathrm{Ag}_{2} \mathrm{S} \), known for its black color, is a desired compound in some industrial applications.

These insights into silver compound formation not only aid in laboratory practices but also play a significant role in various industries, from photography to electronics.