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The P-Block Elements

Question
CBSEENCH12010130
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How do you prepare:


(i) K2MnO4 from MnO2?


(ii) Na2Cr2O7 from Na2CrO4?

Solution

i) K2MnO4 can be prepared from pyrolusite (MnO2). The ore is fused with KOH in the presence of either atmospheric oxygen or an oxidising agent, such as KNO3 or KClO4, to give K2MnO4.
2 MnO2 + 4 KOH + O2   rightwards arrow with increment on top2 K2MnO4 +2H2O
                                     green
ii) Na2Cr2O7 can be prepared from Na2CrO4 in the following way:


For the preparation of sodium dichromate, the yellow solution of sodium chromate is acidified with sulphuric acid to give a solution from which orange sodium dichromate, Na2Cr2O7.2H2O can be crystallised.


Balanced equation for above reactions is as follows:


2 Na2CrO4 + 2H+ ---> Na2Cr2O7 + 2 Na+ + H2O

   Yellow                     Orange

Some More Questions From The p-Block Elements Chapter

Why are pentahalides more covalent than trihalides?

Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?

Why is N2 less reactive at room temperature?

Mention the conditions required to maximise the yield of ammonia.

What is the covalency of nitrogen in N2O5?

Bond angle in PH4+ is higher than that in PH3. Why?

Write a balanced equation for the hydrolytic reactions PCl5 in heavy water.

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