Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing $pH$ on a solution of potassium dichromate?
(N/A) Potassium dichromate is prepared from chromite ore $(FeCr_2O_4)$ in the following steps:
Step $(1):$ Preparation of sodium chromate
$4FeCr_2O_4 + 16NaOH + 7O_2 \longrightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O$
Step $(2):$ Conversion of sodium chromate into sodium dichromate
$2Na_2CrO_4 + 2H^+ \longrightarrow Na_2Cr_2O_7 + H_2O$
Step $(3):$ Conversion of sodium dichromate to potassium dichromate
$Na_2Cr_2O_7 + 2KCl \longrightarrow K_2Cr_2O_7 + 2NaCl$
Potassium dichromate is less soluble than sodium chloride and is obtained as orange-colored crystals.
The dichromate ion $(Cr_2O_7^{2-})$ exists in equilibrium with the chromate ion $(CrO_4^{2-})$ at $pH \approx 4$. Increasing the $pH$ (making the solution more basic) shifts the equilibrium towards the formation of chromate ions $(CrO_4^{2-})$ according to the reaction: $Cr_2O_7^{2-} + 2OH^- \longrightarrow 2CrO_4^{2-} + H_2O$.
Step $(1):$ Preparation of sodium chromate
$4FeCr_2O_4 + 16NaOH + 7O_2 \longrightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O$
Step $(2):$ Conversion of sodium chromate into sodium dichromate
$2Na_2CrO_4 + 2H^+ \longrightarrow Na_2Cr_2O_7 + H_2O$
Step $(3):$ Conversion of sodium dichromate to potassium dichromate
$Na_2Cr_2O_7 + 2KCl \longrightarrow K_2Cr_2O_7 + 2NaCl$
Potassium dichromate is less soluble than sodium chloride and is obtained as orange-colored crystals.
The dichromate ion $(Cr_2O_7^{2-})$ exists in equilibrium with the chromate ion $(CrO_4^{2-})$ at $pH \approx 4$. Increasing the $pH$ (making the solution more basic) shifts the equilibrium towards the formation of chromate ions $(CrO_4^{2-})$ according to the reaction: $Cr_2O_7^{2-} + 2OH^- \longrightarrow 2CrO_4^{2-} + H_2O$.
Explore More
Similar Questions
Manganese steel is used for making railway tracks because
Easy
View SolutionGiven below are two statements:
Statement $I$: Fusion of $MnO_2$ with $KOH$ and an oxidising agent gives dark green $K_2MnO_4$.
Statement $II$: Manganate ion on electrolytic oxidation in alkaline medium gives permanganate ion.
In the light of the above statements,choose the correct answer from the options given below.
Statement $I$: Fusion of $MnO_2$ with $KOH$ and an oxidising agent gives dark green $K_2MnO_4$.
Statement $II$: Manganate ion on electrolytic oxidation in alkaline medium gives permanganate ion.
In the light of the above statements,choose the correct answer from the options given below.
Match the following:
List-$I$ List-$II$ $A$. $Co^{2+}$ $I$. Yellow colour $B$. $Fe^{2+}$ $II$. Dark green colour $C$. $Ni^{2+}$ $III$. Blue colour $D$. $Cu^{2+}$ $IV$. Pale green colour $V$. Pink colour
The correct answer is
| List-$I$ | List-$II$ |
|---|---|
| $A$. $Co^{2+}$ | $I$. Yellow colour |
| $B$. $Fe^{2+}$ | $II$. Dark green colour |
| $C$. $Ni^{2+}$ | $III$. Blue colour |
| $D$. $Cu^{2+}$ | $IV$. Pale green colour |
| $V$. Pink colour |
The correct answer is
When a mixture of $NaCl$,$K_{2}Cr_{2}O_{7}$ and conc. $H_{2}SO_{4}$ is heated in a dry test tube,a red vapour $(X)$ is evolved. This vapour $(X)$ turns an aqueous solution of $NaOH$ yellow due to the formation of $Y$. $X$ and $Y$,respectively,are
Corundum is
Easy
View SolutionVedclass Products
For Students
Vedclass Test Series
Mock tests in real JEE/NEET style with performance analysis. 5-day free trial.
Start Free TrialFor Teachers
Exam Paper Generator
Generate Set A/B/C/D exam papers from 7.5L+ questions in 2 minutes. 3 chapters free.
Try FreeFor Institutes
Online Exam Module
Live online exams with unlimited students, 360° analytics & white-label branding.
See Demo