The oxidation number of chromium in the dichromate ion, Cr2O7 2-, is
Correct answer: C. plus 6
- A. plus 3
- B. plus 12
- C. plus 6
- D. plus 7
Explanation
Seven oxygens contribute minus 14, and the overall charge is minus 2, so the two chromium atoms must total plus 12, giving plus 6 each. Quoting plus 12 forgets to divide between the two atoms, which is the commonest slip. Acidified dichromate is reduced to the green chromium three ion, and that colour change is used as a test for a reducing agent.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? support@testustad.com
About Oxidation and Reduction
Oxidation involves loss of electrons, increase in oxidation number or addition of oxygen, while reduction involves electron gain, decrease in oxidation number or removal of oxygen. The topic covers oxidising and reducing agents, oxidation-number changes, redox equations and the distinction between oxidation at the anode and reduction at the cathode.
Practise Electrochemistry
696 free Electrochemistry MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Chemistry questions like this
Chemistry is on 14 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Oxidation and Reduction questions
The oxidation number of oxygen in hydrogen peroxide, H2O2, is
An oxidising agent is a substance that
The oxidation number of sulphur in sulphuric acid, H2SO4, is
In the reaction 2Na + Cl2 gives 2NaCl, chlorine acts as
The oxidation number of an element in its free, uncombined state is
Oxidation numbers of X, Y, Z are +6, -2 and -1 respectively. Possible molecular formula when atoms combine: