JAMB Chemistry 2009 Objective — Question 22

Question 22 of 50 from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2009 Objective paper, with the correct answer and a full explanation.

Potassium heptaoxodichromate (VI) solution has an orange colour. When the Cr6+ is reduced to Cr3+, the colour changes to

A. yellow
B. greenCorrect
C. blue
D. red

Explanation

K=+1, O=-2, Cr=? (K2Cr2O7). (1x2)+2Cr+(-2x7)=0. 2+2Cr-14=0. 2Cr-12=0. 2Cr=+12. Cr=+6/2=+6. When reduced to Cr3+, the colour changes to green.

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