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प्रश्न
When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C) can be crystallised from the solution. When compound (C) is treated with KCl, orange crystals of compound (D) crystallise out. Identify A to D and also explain the reactions.
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उत्तर
The compounds A, B, C and D are given as under:
A = \[\ce{FeCr2O4}\]
B = \[\ce{Na2CrO4}\]
C = \[\ce{Na2Cr2O7.2H2O}\]
D = \[\ce{K2Cr2O7}\]
The reactions are explained as under:
\[\ce{\underset{(A)}{4FeCr2O4} + 8NaCO3 + 7O2 -> \underset{(B)}{8Na2CrO4} + 2Fe2O3 + 8CO2}\]
\[\ce{2NaCrO4 + 2H^+ -> Na2CrO7 + 2Na^+ + H2O}\]
\[\ce{\underset{(C)}{Na2CrO7} + 2KCl -> \underset{(D)}{K2Cr2O7} + 2NaCl}\]
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संबंधित प्रश्न
Why do the transition elements have higher enthalpies of atomisation?
Give reasons:
Transition metals show variable oxidation states.
Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?
Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
How would you account for the following:
The d1 configuration is very unstable in ions.
Calculate the number of unpaired electrons in the following gaseous ions:
Mn3+, Cr3+, V3+ and Ti3+. Which one of these is the most stable in an aqueous solution?
How would you account for the following?
Transition metals and their compounds act as catalysts.
Write balanced chemical equations for the conversion of `CrO_4^(2-)` to `Cr_2O_7^(2-)` in acidic medium and `Cr_2O_7^(2-)` to `CrO_4^(2-)`
in basic medium.
Dissociation of H2S is suppressed in acidic medium.
Which of the following statements is not correct?
When acidified \[\ce{K2Cr2O7}\] solution is added to \[\ce{Sn^{2+}}\] salts then \[\ce{Sn^{2+}}\] changes to ______.
Match the properties given in Column I with the metals given in Column II.
| Column I (Property) | Column II (Metal) | |
| (i) | An element which can show +8 oxidation state | (a) \[\ce{Mn}\] |
| (ii) | 3d block element that can show | (b) \[\ce{Cr}\] |
| upto +7 oxidation state | (c) \[\ce{Os}\] | |
| (iii) | 3d block element with highest melting point | (d) \[\ce{Fe}\] |
Assertion (A): Cu cannot liberate hydrogen from acids.
Reason (R): Because it has positive electrode potential.
Assertion: The highest oxidation state of osmium is +8.
Reason: Osmium is a 5d-block element.
Account for the following:
In case of transition elements, ions of the same charge in a given series show progressive decrease in radius with increasing atomic number.
Catalytic hydrogenation of benzene gives
Give reason for the following statement:
Physical and chemical properties of the 4d and 5d series of the transition elements are quite similar to expected.
Which of the following characteristics of transition metals is associated with their catalytic activity?
Explain the use of different transition metals as catalysts.
Decide which of the following atomic numbers are the atomic numbers of the inner transition elements:
29, 59, 74, 95, 102, 104
