Name: Oxidation Number and Its Calculations
Uploaded: 2019-07-19
Duration: 6 min 46 s
Description: This video explains what oxidation numbers are and the rules for assigning them to an atom or group of atoms. Also, observe two exercises for better understa...

Question

Assign $ON$ to atoms of only those elements which undergo $ON$ change in the following redox reactions, and then balance the equations.

$H_{2} S + {Cr}_{2} O_{7}^{2 -} + H^{+} \to {Cr}^{3 +} + S_{8} + H_{2} O$

Accepted Answer

Any chemical reaction can be balanced by either oxidation number method or ion electron method.

Here, balancing the given reaction by oxidation number method.

Rules for oxidation number method:

1. Select the oxidant and reductant in the given chemical reaction.

2. Calculate the number of electrons gained or lost by them.

3. Now, multiply the oxidizing agent by the number of lost and reducing agent by the number of gained electrons.

4. Balance the number of atoms on both side whose oxidation number changes in the reaction.

5. To balance the oxygen atoms, add $H_{2} O$ molecules to the deficient side.

6. To balance hydrogen atoms, add $H^{+}$ ion on the deficient side.

Reaction given : $H_{2} S + {Cr}_{2} O_{7}^{2 -} + H^{+} \to {Cr}^{3 +} + S_{8} + H_{2} O$

For the change in number of atoms and balancing,

$3 H_{2} S + {Cr}_{2} O_{7}^{2 -} + 8 H^{+} \overset{}{\to} 2 {Cr}^{3 +} + 3 S + 7 H_{2} O$

Here, oxidation number of sulphur increases from $- 2 (H_{2} S)$ to $0 (S)$ .

Total increase in oxidation number = $2 \times 3 = 6$

And oxidation number of chromium decreases from $+ 6 ({Cr}_{2} O_{7}^{2 -})$ to $+ 3 ({Cr}^{3 +})$ .

Total decrease in oxidation number of chromium = $2 \times 3 = 6$

Assign $ON$ to atoms of only those elements which undergo $ON$ change in the following redox reactions, and then balance the equations.

$H_{2} S + {Cr}_{2} O_{7}^{2 -} + H^{+} \to {Cr}^{3 +} + S_{8} + H_{2} O$

Important Questions on Oxidation Number and Balancing of Redox Reactions

Learn and Prepare for any exam you want !

Assign ON to atoms of only those elements which undergo ON change in the following redox reactions, and then balance the equations. H2S+Cr2O72-+H+→Cr3++S8+H2O

Important Questions on Oxidation Number and Balancing of Redox Reactions

Learn and Prepare for any exam you want !

Assign $ON$ to atoms of only those elements which undergo $ON$ change in the following redox reactions, and then balance the equations.

$H_{2} S + {Cr}_{2} O_{7}^{2 -} + H^{+} \to {Cr}^{3 +} + S_{8} + H_{2} O$