Advertisements
Advertisements
प्रश्न
The \[\ce{E^{\circ}_{(M^{2+}/M)}}\] value for copper is positive (+0.34 V). What is possible reason for this? (Hint: consider its high ΔaH° and low ΔhydH°)
Advertisements
उत्तर
For a metal, \[\ce{E^{\circ}_{(M^{2+}/M)}}\] is related to the sum of the enthalpy changes in the following terms:
\[\ce{M_{(s)} + \Delta_{{a}}H -> M_{(g)}}\] (ΔaH = atomic enthalpy = positive)
\[\ce{M_{(g)} + \Delta_{{i}}H -> M^{2+}_{ (g)}}\] (ΔiH = ionization enthalpy = positive)
\[\ce{M^{2+}_{ (g)} + \Delta_{hyd}H -> M^{2+}_{ (aq)}}\] (ΔhydH = hydration enthalpy = negative)
Copper has a high atomic enthalpy and a low hydration enthalpy. Hence the value of \[\ce{E^{\circ}_{(Cu^{2+}/Cu)}}\] is positive. Hence, the high energy of transformation of Cu(s) into \[\ce{Cu^{2+}_{ (aq)}}\] is not balanced by its hydration enthalpy.
APPEARS IN
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)
Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
An antifriction alloy made up of antimony with tin and copper, which is extensively used in machine bearings is called _______.
(A) Duralumin
(B) Babbitt metal
(C) Spiegeleisen
(D) Amalgam
Explain why Zn2+ salts are white whereas Cu2+ salts are coloured.
Read the passage given below and answer the following question:
The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.
In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.
Assertion: Cations of transition elements occur in various valence states.
Reason: Large number of oxides of transition elements are possible.
\[\ce{KMnO4}\] acts as an oxidising agent in acidic medium. The number of moles of \[\ce{KMnO4}\] that will be needed to react with one mole of sulphide ions in acidic solution is ______.
Which of the following will not act as oxidising agents?
(i) \[\ce{CrO3}\]
(ii) \[\ce{MoO3}\]
(iii) \[\ce{WO3}\]
(iv) \[\ce{CrO^{2-}4}\]
Why does copper not replace hydrogen from acids?
Why EΘ values for Mn, Ni and Zn are more negative than expected?
Assertion: Separation of \[\ce{Zr}\] and \[\ce{Hf}\] is difficult.
Reason: Because \[\ce{Zr}\] and \[\ce{Hf}\] lie in the same group of the periodic table.
Answer the following question:
Which element of the first transition series has lowest enthalpy of atomisation?
Transition metals can act as catalysts because these can change their oxidation state. How does \[\ce{Fe(III)}\] catalyse the reaction between iodide and persulphate ions?
On the basis of the figure given below, answer the following questions:
- Why Manganese has lower melting point than Chromium?
- Why do transition metals of 3d series have lower melting points as compared to 4d series?
- In the third transition series, identify and name the metal with the highest melting point.
Assertion (A): Transition metals show their highest oxidation state with oxygen.
Reason (R): The ability of oxygen to form multiple bonds to metals.
Account for the following:
Eu2+ with electronic configuration [Xe]4f76s2 is a strong reducing agent.
In order to protect iron from corrosion, which one will you prefer as a sacrificial electrode, Ni or Zn? Why? (Given standard electrode potentials of Ni, Fe and Zn are -0.25 V, -0.44 V and -0.76 V respectively.)
What is the oxidation state of chromium in chromate ion and dichromate ion?
Write the ionic equation for reaction of KI with acidified KMnO4.
