How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore ?

Question

How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore ? (A) By the action of concentrated sulphuric acid (B) By roasting with soda ash (C) By the action of sodium hydroxide (D) By the action of lime stone

Tardigrade Admin · Accepted Answer

By the action of concentrated sulphuric acid, sodium chromate gets converted into sodium dichromate in the manufacture of potassium dichromate.

Various steps involved are:

Step I Concentration of the chromite ore by Wilfley method.

Step II Conversion of the concentrated chromite ore into

N a_{2} C r O_{4}

. Concentrated chromite ore is fused with molten

N a_{2} C O_{3}

in the presence of air when

N a_{2} C r O_{4}

and

F e_{2} O_{3}

are formed.

Step III Conversion of

N a_{2} C r O_{4}

into

N a_{2} C r_{2} O_{7}

Aqueous solution of

N a_{2} C r O_{4}

is acidified to obtain

N a_{2} C r_{2} O_{7}

N a_{2} C r O_{4} + H_{2} (D i l) S O_{4} ⟶ N a_{2} C r_{2} O_{7} + H_{2} O

Q. How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore ?

By the action of concentrated sulphuric acid

By roasting with soda ash

By the action of sodium hydroxide

By the action of lime stone