Question

On heating a mixture of $NaCl,{{K}_{2}}C{{r}_{2}}{{O}_{7}}$ and conc. ${{H}_{2}}S{{O}_{4}}$ what is obtained?

Answer 1

Hint: When sodium chloride is reacted with potassium dichromate there is no change in oxidation state of chromium. The oxidation state of chromium remains $+6$ throughout the reaction.

Complete answer:
Potassium dichromate is an inorganic chemical reagent commonly used as an oxidising agent. Its chemical formula is ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$. It is an ionic compound with two potassium ions and negatively charged dichromate ions $(C{{r}_{2}}O_{7}^{-})$. The two hexavalent chromium atoms having oxidation no. $6$ are attached to three oxygen atoms as well as a bridging oxygen atom.
Potassium dichromate is red-orange in colour and normally exists in solid state at room temperature. It is mainly used in production of potassium chrome alum and in the leather tanning industry.
When a mixture of potassium dichromate $({{K}_{2}}C{{r}_{2}}{{O}_{7}})$ and sodium chloride $(NaCl)$is heated in the presence of conc. ${{H}_{2}}S{{O}_{4}}$then a red fuming liquid is formed.
${{K}_{2}}C{{r}_{2}}{{O}_{7}}+4NaCl+6{{H}_{2}}S{{O}_{4}}\to 2KHS{{O}_{4}}+4NaHS{{O}_{4}}+2Cr{{O}_{2}}C{{l}_{2}}+3{{H}_{2}}O$
The chromyl chloride formed produces red fumes.
Chromyl chloride is a reddish brown compound that is liquid at room temperature. It is mainly used as an oxidising agent. It is used for the oxidation of toluene to benzaldehyde. Two oxygen atoms are connected to chromium atoms via double bonds and two chlorine atoms are connected to chromium atoms by single bonds. It has a tetrahedral structure.
When this chromyl chloride is passed through a solution of sodium hydroxide then it turns yellow due to the formation of sodium chromate.
$Cr{{O}_{2}}C{{l}_{2}}+4NaOH\to N{{a}_{2}}Cr{{O}_{4}}+2NaCl+2{{H}_{2}}O$
Yellow colour is formed due to the formation of sodium chromate $(N{{a}_{2}}Cr{{O}_{4}})$.
Sodium chromate is an inorganic compound. It exists as a yellow hygroscopic solid. In this chromium atom is the central atom connected to four oxygen atoms. Two oxygen atoms are connected via double bonds and the other two oxygen atoms are connected by single bonds which are further attached to the sodium atom.

Note:
Such reactions are vigorous as they involve heating in between the reaction and fumes are produced in the end product.