Chemistry Class 12
Solutions to CBSE Sample Paper - Chemistry Class 12

a. Why are all copper halides known except that copper iodide?

b. Why is the E o (V3+/V2+) value for vanadium comparatively low?

c. Why HCl should not be used for potassium permanganate titrations?

d. Explain the observation, at the end of each period, there is a slight increase in the atomic radius of d block elements.

e. What is the effect of pH on dichromate ion solution?



a. Cu 2+ oxidizes iodide ion to iodine.

b. The low value for V is related to the stability of V 2+ (half-filled t 2g level)

c. Permanganate titrations in presence of hydrochloric acid are unsatisfactory since hydrochloric acid is oxidised to chlorine.

d. The d orbital is full with ten electrons and shield the electrons present in the higher s-orbital to a greater extent resulting in increase in size.

e. The chromates and dichromates are interconvertible in aqueous solution depending upon pH of the solution. Increasing the pH (in basic solution)of dichromate ions a colour change from orange to yellow is observed as dichromate ions change to chromate ions.

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.