Potassium Dichromate
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12 Terms
K2Cr2O7
Potassium dichromate
chromite ore
FeO * Cr2O3
Prep STEP 1
chromite ore fused with Na2CO3 in presence of air to give Na2CrO4
STEP 2
yellow sol. of Na2CrO4 is filtered, acidified with sulfuric acid to give sol. from which Na2Cr2O7 is crystallized
Why is K2Cr2O7 prepared by treating solution of Na2Cr2O7 with KCl
because sodium dichromate is more soluable than potassium dichromate
Why is K2Cr2O7 preferred as primary standard in titration
because Na2Cr2O7 is hygroscopic in nature but K2Cr2O7 is not
(CrO4)-2 ————> (Cr2O7)-2 colour change? and what reagent
Yellow to orange
fwd > H+
bwd > OH-
Effect of heating
strong heating > decomposes with liberating oxygen
Oxidizing agent in what medium
Acidic medium
Chromyl chloride test
to identify ionic chlorides
K2Cr2O7 on reaction with NaCl and H2SO4
gives CrO2Cl2 (red orange vapour) further reaction with NaOH sol. gives Na2CrO4
Acidified K2Cr2O7 reacts with H2O2 in etheral sol.
gives deep blue sol. due to the formation of CrO5
Note 
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