Question

The salt which gives a dirty green precipitate with NaOH solution and a white precipitate with \[BaC{l_2}\] solution is:
A.Iron [III] sulphate
B.Iron [II] sulphate
C.Iron [II] chloride
D.Iron [III] chloride

Answer 1

Hint: To solve this question, we must first determine the products obtained by reacting NaOH with the given compounds. Then we can cross reference the colour of the precipitates with their standard colours to find the answers.

Complete step by step answer:
Before we move forward with the solution of the given question, let us first understand some important basic concepts.
To determine the correct answer, we must first discuss the different products that are formed by the reaction of the given compounds with NaOH.
A.Iron [III] sulphate:
Iron [III] sulphate or ferric sulphate reacts with NaOH to form sodium sulphate along with iron [III] hydroxide. This iron [III] hydroxide precipitates in the form of a brown coloured solid.
 \[F{e_2}{(S{O_4})_3} + 6NaOH \to 2Fe{(OH)_3} + 3N{a_2}S{O_4}\]
B.Iron [II] sulphate:
Iron [II] sulphate or ferrous sulphate with NaOH to form sodium sulphate along with iron [II] hydroxide. This iron [II] hydroxide precipitates in the form of a green coloured solid.
 \[FeS{O_4} + 2NaOH \to Fe{(OH)_2} + N{a_2}S{O_4}\]
C.Iron [II] chloride:
Iron [II] chloride or ferrous chloride reacts with NaOH to form sodium chloride along with iron [III] hydroxide. This iron [II] hydroxide precipitates in the form of a green coloured solid, which after some time turns into a reddish-brown colour.
 \[FeC{l_2} + 2NaOH \to Fe{(OH)_2} + 2NaCl\]
D.Iron [III] chloride:
Iron [III] chloride or ferric chloride reacts with NaOH to form sodium chloride along with iron [III] chloride This iron [III] hydroxide precipitates in the form of a brown coloured solid.
   \[FeC{l_3} + 3NaOH \to Fe{(OH)_3} + 3NaCl\]

Hence, Option B is the correct option.

Note:
Certain chemical reactions result in the precipitation of insoluble ionic solids which is formed when cations and anions combine in an aqueous solution. Whether or not such a reaction can occur can be determined with the help of solubility rules for common ionic solids.