Which of the following is an oxidation-reduction reaction?
[tex]$SO _2(g)+ H _2 O ( l ) \longrightarrow H _2 SO _3( aq )$[/tex]
[tex]$CaCO _3(s) \longrightarrow CaO ( s )+ CO _2(g)$[/tex]
[tex]$Ca ( OH )_2(s)+ H _2 CO _3( l ) \longrightarrow CaCO _3( aq )+2 H _2 O ( l )$[/tex]
[tex]$C _6 H _{12} O _6(s)+6 O _2(g) \longrightarrow 6 CO _2(g)+6 H _2 O ( l )$[/tex]
Answer (2)
The oxidation-reduction reaction is C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) → 6 C O 2 ( g ) + 6 H 2 O ( l ) , as evidenced by the changes in oxidation states of carbon and oxygen. The other reactions do not involve any changes in oxidation states. Thus, they are not classified as redox reactions.
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Reaction 1, 2, and 3 are not redox reactions because there is no change in the oxidation state of any element.
Reaction 4 is a redox reaction because the oxidation state of C changes from 0 to +4, and the oxidation state of O changes from 0 to -2.
The oxidation-reduction reaction is C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) ⟶ 6 C O 2 ( g ) + 6 H 2 O ( l ) .
Therefore, the answer is C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) ⟶ 6 C O 2 ( g ) + 6 H 2 O ( l ) .
Explanation
Analyzing the Reactions Let's analyze each reaction to determine if it's an oxidation-reduction (redox) reaction. A redox reaction involves a change in oxidation state for at least two elements.
Analyzing Reaction 1 Reaction 1: S O 2 ( g ) + H 2 O ( l ) ⟶ H 2 S O 3 ( a q )
In S O 2 , the oxidation state of S is +4 and O is -2.
In H 2 O , the oxidation state of H is +1 and O is -2.
In H 2 S O 3 , the oxidation state of H is +1, S is +4, and O is -2.
Since there is no change in the oxidation states of any element, this is not a redox reaction.
Analyzing Reaction 2 Reaction 2: C a C O 3 ( s ) ⟶ C a O ( s ) + C O 2 ( g )
In C a C O 3 , the oxidation state of Ca is +2, C is +4, and O is -2.
In C a O , the oxidation state of Ca is +2 and O is -2.
In C O 2 , the oxidation state of C is +4 and O is -2.
Since there is no change in the oxidation states of any element, this is not a redox reaction.
Analyzing Reaction 3 Reaction 3: C a ( O H ) 2 ( s ) + H 2 C O 3 ( l ) ⟶ C a C O 3 ( a q ) + 2 H 2 O ( l )
In C a ( O H ) 2 , the oxidation state of Ca is +2, O is -2, and H is +1.
In H 2 C O 3 , the oxidation state of H is +1, C is +4, and O is -2.
In C a C O 3 , the oxidation state of Ca is +2, C is +4, and O is -2.
In H 2 O , the oxidation state of H is +1 and O is -2.
Since there is no change in the oxidation states of any element, this is not a redox reaction.
Analyzing Reaction 4 Reaction 4: C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) ⟶ 6 C O 2 ( g ) + 6 H 2 O ( l )
In C 6 H 12 O 6 , the oxidation state of C is 0, H is +1, and O is -2.
In O 2 , the oxidation state of O is 0.
In C O 2 , the oxidation state of C is +4 and O is -2.
In H 2 O , the oxidation state of H is +1 and O is -2.
Here, the oxidation state of C changes from 0 to +4, and the oxidation state of O changes from 0 to -2. Therefore, this is a redox reaction.
Conclusion Based on the analysis, the oxidation-reduction reaction is:
C 6 H 12 O 6 ( s ) + 6 O 2 ( g ) ⟶ 6 C O 2 ( g ) + 6 H 2 O ( l )
Examples
Redox reactions are fundamental in many real-world applications. For example, the combustion of fuels like wood or propane is a redox reaction that releases energy in the form of heat and light. Similarly, the rusting of iron is a redox reaction where iron reacts with oxygen in the presence of water to form iron oxide. Understanding redox reactions helps us to develop new technologies, such as batteries and fuel cells, and to prevent corrosion and other unwanted chemical reactions.
