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The oxidation number of chromium changes from…

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CHEMISTRY

Consider the equation below:

The oxidation number of chromium changes from

The oxidation number of chromium changes from

  • A. +5 to +3
  • B. +6 to +3
  • C. -2 to +3
  • D. +7 to +3

QUICK ANSWER…

B

SOLUTION 

From the options, it is obvious we don’t have a problem with the oxidation state of chromium on the right-hand side. Hence, lets focus on the left-hand side.

Oxidation state of chromium on the left-hand side of the equation =

2(Cr) + 7(O) = – 2

2(Cr) + 7(-2) = – 2

2(Cr) – 14  = – 2

2(Cr) = – 2 + 14

2(Cr) = 12

Therefore, Cr = 12/2 = +6

Option B

Now for the right answer to the above question:

  1. Option A is incorrect.
  2. Option B is correct.
  3. C is incorrect.
  4. D is not the correct answer.

QUICK TIPS…

You may please note these/this:

  • Known oxidation number of other atoms are often used to derive that of the unknown as illustrated above.

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/ culled from 2019 JAMB-UTME Chemistry question 40 /

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