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How would you prepare (i) K(2)MnO(4) ...

How would you prepare
(i) `K_(2)MnO_(4)` and `MnO_(2)`? (ii) `Na_(2)Cr_(2)O_(7)` from `Na_(2)CrO_(4)` ?

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(i)`MnO_(2)` is fused with KOH in the presence of oxygen (air).
`4KOH+2MnO_(2)+O_(2) overset(Heat) to 2K_(2)MnO_(4)+2H_(2)O`
(ii) `2Na_(2)CeO_(4)` is treated with dilute `H_(2)SO_(4)`.
`2Na_(2)CrO_(4)+H_(2)SO_(4) to Na_(2)Cr_(2)O_(7)+Na_(2)SO_(4)+H_(2)O`
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How do you prepare : (i) k_(2)MnO_(4) from MnO_(2) ? (ii) Na_(2)Cr_(2)O_(7) from NaCrO_(4) ? (b) Account for the following : (i) Mn^(2+) is more stable then Fe^(2+) towards oxidation to + 3 state. (ii) The enthelpy of atomization is lowest for Zn in 3d series of the transition elements. (iii) Actinoid elements show wide range of oxidation states.

K_(2)Cr_(2)O_(7)+NaoH to CrO_(4)^(2-)

Na_(2)CrO_(4)+HCl to H_(2)Cr_(2)O_(7)+Na_(2)SO_(4)

FeCr_(2)O_(4)+Na_(2)CO_(3)+O_(2) to Fe_(2)O_(3)darr+Na_(2)CrO_(4)

Potassium dichromate (K_(2)Cr_(2)O_(7)) is an orange coloured compound , very frequently used in laboratory as an oxidising agent as well as in a redox titration. It is generally prepared from chromite (FeCr_(2)O_(4)) ore according to the following reactions: (1) Fusion of chromite ore with sodium carbonate in excess of air. FeCr_(2)O_(4) + Na_(2)CO_(3) + O_(2) rarr Na_(2)CrO_(4)+Fe_(2)O_(3) +CO_(2) (2) Acidifing filtered sodium chromate solution with sulphuric acid. Na_(2)CrO_(4) + H_(2)SO_(4) rarr Na_(2)Cr_(2)O_(7) + Na_(2)SO_(4) + H_(2)O (3) Treating sodium dichormate with potassium choride . Na_(2)Cr_(2)O_(7) + KCl rarr K_(2)Cr_(2)O_(7) + NaCl If the number of moles of reactant available for reaction are : [FeCr_(2)O_(4)=0.25 "moles" , O_(2)=0.35 "moles", Na_(2)CO_(3)=0.60 "moles", H_(2)SO_(4)=0.2 "moles", KCl=0.4 "moles"] , then the maximum number of moles of K_(2)Cr_(2)O_(7) , that can be produced is :

DINESH PUBLICATION-D-AND -F BLOCK ELEMENTS-Question From Board Examination
  1. What do you mean by (a) Chromyl Chloride test (b) Actinoids?

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  2. Why do transition metals form coloured complexes ?

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  3. How would you prepare (i) K(2)MnO(4) and MnO(2)? (ii) Na(2)Cr(2)O(7...

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  4. Why is enthalpy of atomisation is the lowest for Zn in 3d series of tr...

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  5. Why is Cr^(2+) reducing and Mn^(3+) oxidising when both have d^4 confi...

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  6. Which of the following actinoids is well known to exhibit +2 oxidation...

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  7. Why do actinoid elements show wide range of oxidation states ?

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  8. Why do the transition elements exhibit higher enthalpies of atomisatio...

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  9. (i) Write an oxidising reaction of K(2)Cr(2)O(7) in the acidic medium....

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  10. Silver atom has completely filled d orbitals (4d^(10)) in its ground s...

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  11. Explain actinoid contraction .

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  12. Why do transition elements show variable oxidation state?

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  13. Explain the following properties of transition elements. (i) Variab...

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  14. Describe the preparation of potassium dichromate from chromite ore. Wh...

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  15. (a) What is Lanthanoids contraction ? (b) What are Interstial compou...

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  16. Complete the following : 3MnO(4)^(2-)+4H^(+) to

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  17. How will you account for the following : (a) (i) The chemistry of act...

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  18. (a) How would you account for the following : (i) Actinoids contract...

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  19. (i) Account for the fact that Eu^(2+) is a strong reducing agent. (...

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  20. {:(E(M^(2+)//M)^(@),Cr,Mn, Fe, Co, Ni, Cu),(,-0.91,-1.18,-0.44,-0.28,-...

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