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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
Which of the following cations are coloured in aqueous solutions and why ?
Sc3+, V3+, Ti4+, Mn2+ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)
Calculate magnetic moment of `Fe_((aq))^(2+) ion (Z=26).`
How would you account for the following: Transition metals form complex compounds.
Why are Mn2+ compounds more stable than Fe2+ towards oxidation to their +3 state?
What may be the stable oxidation state of the transition element with the following d electron configuration in the ground state of its atom?
3d3
What are the characteristics of the transition elements and why are they called transition elements?
Why do transition metal ions possess a great tendency to form complexes?
Metallic radii of some transition elements are given below. Which of these elements will have highest density?
| Element | \[\ce{Fe}\] | \[\ce{Co}\] | \[\ce{Ni}\] | \[\ce{Cu}\] |
| Metallic radii/pm | 126 | 125 | 125 | 128 |
Why is \[\ce{HCl}\] not used to make the medium acidic in oxidation reactions of \[\ce{KMnO4}\] in acidic medium?
Match the solutions given in Column I and the colours given in Column II.
| Column I (Aqueous solution of salt) |
Column II (Colour) |
| (i) \[\ce{FeSO2.7H2O}\] | (a) Green |
| (ii) \[\ce{NiCl2.4H2O}\] | (b) Light pink |
| (iii) \[\ce{MnCl2.4H2O}\] | (c) Blue |
| (iv) \[\ce{CoC12,6H2O}\] | (d) Pale green |
| (v) \[\ce{Cu2 Cl2}\] | (e) Pink |
| (f) Colourless |
Assertion: The highest oxidation state of osmium is +8.
Reason: Osmium is a 5d-block element.
When an oxide of manganese (A) is fused with KOH in the presence of an oxidising agent and dissolved in water, it gives a dark green solution of compound (B). Compound (B) disproportionates in neutral or acidic solution to give purple compound (C). An alkaline solution of compound (C) oxidises potassium iodide solution to a compound (D) and compound (A) is also formed. Identify compounds A to D and also explain the reactions involved.
The orientation of an atomic orbital is governed by
Why Zn, Cd and Hg are not called transition metals?
How is the variability in oxidation states of transition metals different from that of p-block elements?
The number of terminal oxygen atoms present in the product B obtained from the following reactions is:
\[\ce{FeCr2O4 + Na2CO3 + O2 -> A + Fe2O3 + CO2}\]
\[\ce{A + H^+ -> B + H2O + Na^+}\]
Consider the following standard electrode potentials (E° in volts) in aqueous solution:
| Element | M3+/M | M+/M |
| Al | - 1.66 | +0.55 |
| Tl | + 1.26 | -0.34 |
Based on these data, which of the following statements is correct?
Write the number of unpaired electrons in Cr3+.
(Atomic number of Cr = 24)
Give a reason for the following:
Zinc, cadmium and mercury are considered as d-block elements but not regarded as transition elements.
Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following point:
Ionisation enthalpies
