Determine whether each change represents oxidation or reduction.

Question 1

Determine whether each of the following changes represents oxidation or reduction.

OXID-REDUC

Question 2

Determine whether a change of CH4CH4 to CO2CO2 represents oxidation or reduction.

Question 3

Determine whether a change of CH3OHCH3OH to CH4CH4 represents oxidation or reduction.

Answer to question 1

Oxidation and Reduction

  • Conversion of iron from its +3 oxidation state to +2 oxidation state is reduction.
  • Formation of carbon dioxide after removal of oxygen is a reduction.
  • Formation of alkane from alcohol is reduction.
  • Conversion of Ag+1 to Ag is reduction.
  • Formation of C2H8O2C2H8O2 is oxidation.
  • The increase in charge of NO from -3 to -2 is oxidation.
  • The formation of carboxylic acid from aldehyde is oxidation.
  • The conversion of Cu to Cu2+ is oxidation.
  • The conversion of the ketone to alcohol is reduction.

Answer to question 2

To answer the question we need to first assign oxidation states to the methane reactant shown:

CH4CH4

  • Carbon and hydrogen atoms are present, with carbon being more electronegative.
  • Each hydrogen atom receives its preferred positive oxidation state of +1.
  • Therefore, to balance, the carbon atom receives a negative oxidation state of -4.

Now we assign oxidation states to the carbon dioxide product:

CO2CO2

  • Carbon and oxygen atoms are present, with oxygen being more electronegative.
  • Each oxygen atom receives its preferred negative oxidation state of -2.
  • Therefore, to balance the carbon receives a positive oxidation state of +4.

The assignments show that carbon increases its oxidation state from -4 to +4. Therefore, the carbon atom is undergoing oxidation.

Answer to question 3

The change represents reduction.

Explanation:

Let’s investigate the half-equation for the change from CH3OHCH3OH to CH4CH4. Here, we will assume acidic conditions, as conditions are not relevant for the overall process.

Step 1. Balance the number of oxygen atoms.

CH3OH→CH4+H2OCH3OH→CH4+H2O

Step 2. Balance the hydrogen atoms using H+H+.

CH3OH+2H+→CH4+H2OCH3OH+2H+→CH4+H2O

Step 3. Balance the charge.

CH3OH+2H++2e−→CH4+H2OCH3OH+2H++2e−→CH4+H2O

In the reaction, we observe a gain in electrons. Therefore, the change is a reduction process.

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