Question 14 Marks
Read the following text carefully and answer the questions that follow:
Transition metal oxides are generally formed by the reaction of metals with oxygen at high temperatures. The highest oxidation number in the oxides coincides with the group number. In vanadium, there is a gradual change from the basic V2O3 to less basic V2O4 and to amphoteric V2O5. V2O4 dissolves in acids to give VO2+ salts. Potassium dichromate is a very important chemical used in the leather industry and as an oxidant for the preparation of many azo compounds. Dichromates are generally prepared from chromate. Sodium dichromate is more soluble than potassium dichromate. The latter is, therefore, prepared by treating the solution of sodium dichromate with potassium chloride. Sodium and potassium dichromates are strong oxidising agents; sodium salt has a greater solubility in water and is extensively used as an oxidising agent in organic chemistry. Potassium dichromate is used as a primary standard in volumetric analysis.
i. Which of the 3d series of the transition metals exhibits the largest number of oxidation and why?
ii. A transition metal exhibits highest oxidation state ih oxides and fluorides. Give reason.
iii. How would you account for the increasing oxidising power in the series:
$VO _2^{+}< Cr _2 O _7^{2-}< MnO _4^{-}$?
Transition metal oxides are generally formed by the reaction of metals with oxygen at high temperatures. The highest oxidation number in the oxides coincides with the group number. In vanadium, there is a gradual change from the basic V2O3 to less basic V2O4 and to amphoteric V2O5. V2O4 dissolves in acids to give VO2+ salts. Potassium dichromate is a very important chemical used in the leather industry and as an oxidant for the preparation of many azo compounds. Dichromates are generally prepared from chromate. Sodium dichromate is more soluble than potassium dichromate. The latter is, therefore, prepared by treating the solution of sodium dichromate with potassium chloride. Sodium and potassium dichromates are strong oxidising agents; sodium salt has a greater solubility in water and is extensively used as an oxidising agent in organic chemistry. Potassium dichromate is used as a primary standard in volumetric analysis.
i. Which of the 3d series of the transition metals exhibits the largest number of oxidation and why?
ii. A transition metal exhibits highest oxidation state ih oxides and fluorides. Give reason.
iii. How would you account for the increasing oxidising power in the series:
$VO _2^{+}< Cr _2 O _7^{2-}< MnO _4^{-}$?
Answer
View full question & answer→i. Manganese (Z = 25) shows maximum number of O.S. This is because its outer EC is 3d54s². As 3d and 4s are close in energy, it has maximum number of e-1 s to loose or share. Hence, it shows O.S. from +2 to +7 which is the maximum number.Page 12 of 14
ii. A transition metal exhibits higher oxidation states in oxides and fluorides because oxygen and fluorine are highly electronegative elements, small in size and strongest oxidising agents.
iii. This is due to the increasing stability of the lower species to which they are reduced.
ii. A transition metal exhibits higher oxidation states in oxides and fluorides because oxygen and fluorine are highly electronegative elements, small in size and strongest oxidising agents.
iii. This is due to the increasing stability of the lower species to which they are reduced.