When an oxide of manganese (A) is fused with KOH in the presence of an oxidizing 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 compounds (A), (B), (C) and (D) are given as under:
Assertion (A): Cu can not libirate hydrogen from acids .
Reason (R): because it has positive electrode potential.
Actinoid contraction is greater from element to element than lanthanoid contraction. Why?
What may be the stable oxidation state of the transition element with the following delectron configurations in the ground state of their atoms: 3d3,3d5, 3d8 and 3d4?
Although fluorine is more electronegative than oxygen, but the ability of oxygen to stabilize higher oxidation states exceeds that of fluorine. Why?
Although +3 is the characteristic oxidation state for lanthanoids but cerium
also shows +4 oxidation state because
(a) it has variable ionization enthalpy
(b) it has a tendency to attain noble gas configuration
(c) it has a tendency to attain f ° configuration
(d) it resembles Pb4+
Although Zr belongs to 4d and Hf belongs to 5d transition series but it is quite difficult to separate them. Why?
In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct answer out of the following choices:
(a) Both Assertion and Reason are true and the Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true and the Reason is not the correct explanation of Assertion.
(c) Assertion is not true but the Reason is true.
(d) Both Assertion and Reason are false.
Assertion (A): Cu2+ iodide is not known.
Reason (R): Cu2+ oxidises I to iodine.
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 crystallized 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.
Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element
KMnO4 acts as an oxidizing agent in acidic medium. The number of moles of KMn04 that will be needed to react with one mole of sulphide ions in acidic solution is
How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?
While filling up of electrons in the atomic orbitals, the 4s orbital is filled before the 3d-orbital but reverse happens during the ionization of the atom. Explain why?
Assertion (A): Actinoids form relatively less stable complexes as compared to lanthanoids.
Reason (R): Actinoids can utilize their 5d orbitals along with 6d orbitals in bonding but lanthanoids do not use their 4f orbital for bonding.
Assertion (A): The highest oxidation state of osmium is +8.
Reason (R): Osmium is a 5d-block element.
Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.
Metallic radii of some transition elements are given below. Which of these elements will have highest density?
Gadolinium belongs to 4f series. Its atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?
Which of the following actinoids show oxidation states up to +7?
(a) Am (b) Pu (c) U (d) Np
Which of the following lanthanoids show +2 oxidation state besides the characteristic oxidation state +3 of lanthanoids?
(a) Ce (b) Eu (c) Yb (d) Ho
A solution of KMnO4 on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out?
While filling up of electrons in the atomic orbitals, the 4s orbital is filled before the 3d-orbital but reverse happens during the ionization of the atom. Explain why?
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 aqueous solution.
When KMnO4 solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because
(a) CO2 is formed as the product (b) Reaction is exothermic
(c) Mn04 catalyses the reaction (d) Mn2+ acts as autocatalyst
When a brown compound of manganese
(A) is treated with HCl, it gives a gas
(B) The gas taken in excess, reacts with NH3 to give an explosive compound
(C) Identify compounds A, B and C.
Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
For M2+/M and M3+/M2+ systems the E ° values for some metals are as follows:
Cr2+/Cr –> -0.9 V
Mn2+/Mn –> -1.2V
Fe2+/Fe –> -0.4 V
Cr3+/Cr2+ –> -0.4 V
Mn3+/Mn2+ –>+ 1.5V
Fe3+/Fe2+ –>+ 0.8V
(ii) the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
Predict which of the following will be coloured in aqueous solution? Ti3+, V3+,Cu+, Sc3+, Mn2+, Fe3+ and Co2+ Give reasons for each.
Which metal in the first series of transition metals exhibits + 1 oxidation state most frequently and why?
The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.
Com pare 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 points:
(i) electronic configurations
(ii) oxidation states
(iii) ionisation enthalpies and
(iv) atomic sizes
Generally, transition-elements and their salts are coloured due to the presence of unpaired electrons in metal ions. Which of the following compounds are coloured?
(a) kMnO4 (b) Ce(SO4)2 (c) TiCl4 (d) Cu2Cl2
General electronic configuration of actinoids is (n – 2)f1-14 (n – 1 )d0-2 ns2. Which of the following actinoids have one electron in 6d orbital?
(a) U (Atomic no. 92) (b) Np (Atomic no. 93)
(c) Pu (Atomic no. 94) (d) Am (Atomic no. 95)
Which of the following ions show higher spin only magnetic moment value?
(a) Ti3+ (b) Mn2+ (c) Fe2+ (d) Co3+
Transition elements form binary compounds with halogens. Which of the following elements will form MF3 type compounds?
(a) Cr (b) Co (c) Cu (d) Ni
Although Cr3+ and CO2+ ions have same number of unpaired electrons but the magnetic moment of Cr3+ is 3.87 BM and that of CO2+ is 4.87 BM. Why?
In the series Sc (Z = 21) to Zn (Z = 30), the enthalpy of atomisation of zinc is the lowest, i.e., 126 kJ mol-1 . Why?
Write down the electronic configuration of (i) Cr3+ (ii) Pm3+ (iii) Cu+ (iv) Ce4+(v) Co2+ (vi) Lu2+(vii) Mn2+ (viii) Th4+.
What are the characteristics of the transition . elements and why are they called transition elements? Which of the d-block elements may not be regarded as the transition elements?
Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with:
(i) iodide
(ii) iron (II) solution and
(iii) H2S
