Question

Which of the following reactions produce a yellow precipitate?
(A) $NaOH(aq){\text{ }} + {\text{ }}HCl(aq){\text{ }} \to {\text{ }}NaCl(s){\text{ }} + {\text{ }}{H_2}O$
(B) $NaOH(aq){\text{ }} + {\text{ }}BaCl(aq){\text{ }} \to {\text{ }}BaOH(s){\text{ }} + {\text{ }}NaCl(aq)$
(C) $Pb{(N{O_3})_2}(aq){\text{ }} + {\text{ }}2KI(aq){\text{ }} \to {\text{ }}2KN{O_3}(aq){\text{ }} + {\text{ }}Pb{I_2}(s)$
(D) $CuO(s){\text{ }} + {\text{ }}Mg(s){\text{ }} \to {\text{ }}Cu(s){\text{ }} + {\text{ }}MgO(s)$

Answer 1

To answer this question you should recall the concept of precipitation reaction and solubility. Precipitation reactions involve the formation of an insoluble salt known as a precipitate from a reaction between two soluble salts. The yellow precipitate formed is a dihalide compound.

Complete step by step solution:
From the options given in the question we can see that the precipitates obtained are: $NaCl$ , $BaOH$ , $Pb{I_2}$ and $MgO$ .
The precipitates $NaCl$ , $BaOH$ and $MgO$ are colorless while the precipitate obtained in the reaction: $Pb{(N{O_3})_2}\left( {aq} \right) + 2KI\left( {aq} \right) \to 2KN{O_3}\left( {aq} \right) + Pb{I_2}\left( s \right)$ i.e. $Pb{I_2}$ is yellow in colour.
When lead nitrate is added to potassium iodide the particles combine and create two new compounds, a yellow solid called lead iodide is formed. This yellow solid indicates that a chemical change has taken place.
Therefore, we can conclude that the correct answer to this question is option C.

Note:
The different types of salts based on their constituents
1. Acidic salt: The salt resulting from partial neutralization of a polyprotic acid is known as an acidic salt. These salts have ionizable ${H^ + }$ ion along with another cation. Example: $NaHS{O_4},{\text{ }}K{H_2}P{O_4}$ etc.
2. Basic or Alkali Salt: This type of salt is formed by the partial neutralization of a strong base by a weak acid is known as a basic salt. These salts hydrolysis to form a basic solution. Example: White lead $(2PbC{O_3}.Pb{\left( {OH} \right)_2}).$
3. Double salt: These types of salts contain more than one cation or anion is known as double salt. They are obtained by the combination of two different salts crystallized in the same ionic lattice. Example: Potassium sodium tartrate $(KNa{C_4}{H_4}{O_6}.4{H_2}O)$ which is also known as Rochelle salt.
4. Mixed Salts: These types of salts are made up of a fixed proportion of two salts, often sharing either a common cation or common anion is known as mixed salt.