With reference to ncert solutions , chapter 8 - redox reactions - exercise question 8.1 (f) NaBH4 does not seem to be a binary compound then how come the oxidation no. of hydrogen (-1) ? I feel it should be (+1) . Request to clarify . Thanks

Asked by dave_nileshin | 25th Nov, 2015, 06:00: AM

Expert Answer:

Sodium borohydride is an ionic compound made up of 2 ions, Na+ (rule 3 gives the oxidation number of sodium ions as +1) and the borohydride ion BH4¯. The sum of the oxidation numbers of boron and hydrogen in BH4¯  ion must be -1.

But we know that hydrogen in metallic hydrides has an oxidation number of -1, and therefore hydrogen contribute -4 to the oxidation number of the ion. This means that boron has an oxidation number of +3.

Answered by Prachi Sawant | 25th Nov, 2015, 10:22: AM