Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with oxalic acid ?
Write the ionic equations for the reactions.
Write the ionic equations for the reactions.
Potassium permanganate is prepared by fusion of MnO₂ with an alkali metal hydroxide and an oxidising agent like KNO₃. This produces the dark green K₂MnO₄ which disproportionates in a neutral or acidic solution to give permanganate.
2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O
3MnO₄²⁻ + 4H⁺ → 2MnO₄ + MnO₂ + 2H₂O
Oxalate ion or oxalic acid is oxidised at 333 K :
5C₂O₄²⁻ + 2MnO₄⁻ + 16H⁺ → 2Mn²⁺ + 8H₂O + 10CO₂
2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O
3MnO₄²⁻ + 4H⁺ → 2MnO₄ + MnO₂ + 2H₂O
Oxalate ion or oxalic acid is oxidised at 333 K :
5C₂O₄²⁻ + 2MnO₄⁻ + 16H⁺ → 2Mn²⁺ + 8H₂O + 10CO₂
Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with (i) an iodide (ii) H₂S.
Explain the following observation :
Most of the transition metal ions exhibit characteristic colour in aqueous solution.
Write the formula of an oxo-anion of Manganese (Mn) in which it shows the oxidation state equal to its group number.
What is meant by ‘disproportionation’ ? Give an example of a disproportionation reaction in aqueous solution.
Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number.
Assign the reason for the following :
Copper (I) ion is not known in aqueous solution.
When Cu²⁺ ion is treated with KI, a white precipitate is formed. Explain the reaction with the help of chemical equation.
The conductivity of metals decreases while that of electrolytes increases with increase in temperature. Why?
The following curve is obtained when molar conductivity is plotted against the square root of concentration, c½ for two electrolytes A and B :
(i) State the law which helps to determine the limiting molar conductivity of weak electrolyte.
(ii) Calculate limiting molar conductivity of CaSO₄ (limiting molar conductivity of calcium and sulphate ions are 119.0 and 160.0 Scm² mol⁻¹ respectively)
The conductivity of an aqueous solution of NaCl in a cell is 92 \(Ω^{−1}\) \(cm^{-1}\) the resistance offered by this cell is 247.8 Ω . Calculate the cell constant.
Explain why :
(i) E° for Mn³⁺/Mn²⁺ couple is more positive than that for Fe³⁺/Fe²⁺. (At. Nos. Mn = 25, Fe = 26).
(ii) Ce³⁺ can be easily oxidized to Ce⁴⁺. (At. No.Ce = 58).
Why a mixture of Carbon disulphide and acetone shows positive deviation from Raoult’s law? What type of azeotrope is formed by this mixture?
Define the following terms :
(i) Molar conductivity (),
(ii) Secondary batteries.