Question

Which of the following are redox reactions? (Select all that apply)a) C2H8(g) + 5O2(g) --> 4H2O(g) + 3CO2(g)b) Mg (s) + 2HCl(aq) --> MgCl2(aq) + H2(g)c) Ag+(aq) + Br- (aq) --> AgBr(s)d) H2CO3(aq) --> H20(I) + CO2(g)e) 2H2O (g) --> 2H2(g) + O2(g)d) NaOH(aq) + HCl(aq) --> NaCl(aq) + H2O(aq)

Answer 1

The following equations below are redox reactions:

`\begin{gathered} a)C_2H_8(g)+5O_2(g)\longrightarrow4H_2O(g)+3CO_2(g) \\ b)Mg(s)+2HCl(aq)\longrightarrow MgCl_2(aq)+H_2(g) \\ e)2H_2O(g)\longrightarrow2H_2(g)+O_2(g) \end{gathered}`

Explanations:

Redox reaction occurs when there is the addition of oxygen and the removal of hydrogen in a chemical reaction. Redox is a type of chemical reaction in which the oxidation states of atoms are changed.

According to the question, we are to determine which of the equation listed undergoes a redox reaction.

a) For the equation

`C_2H_8\mleft(g\mright)+5O_2\mleft(g\mright)\longrightarrow4H_2O\mleft(g\mright)+3CO_2\mleft(g\mright)`

Propane compound C3H8 gains oxygen and loses hydrogen simultaneously to form CO2, Therefore the reaction is a redox

b) For the reaction:

`Mg(s)+2HCl\mleft(aq\mright)\longrightarrow MgCl_2\mleft(aq\mright)+H_2\mleft(g\mright)`

From this equation, you can see that Magnesium metal is being oxidized to magnesium cations, Mg2+. while hydrogen is being reduced from hydrogen ions, H+, to produce hydrogen gas, H2. Hence we can conclude that the reaction is also a redox reaction.

c) For the reaction:

`Ag^+\mleft(aq\mright)+Br^-(aq)\longrightarrow AgBr\mleft(s\mright)`

from the reaction, you can see that the oxidation state of silver in Ag+ and AgBr is +1 and since there is no change in oxidation state, hence the reaction is NOT a redox reaction

d) For the reaction:

`H_2CO_3\mleft(aq\mright)\longrightarrow H_20\mleft(I\mright)+CO_2\mleft(g\mright)`

This is not a redox reaction since the formation of water and carbon dioxide itself undergo a redox reaction.

e) For the chemical reaction

`2H_2O(g)\longrightarrow2H_2\mleft(g\mright)+O_2\mleft(g\mright)`

Hydrogen is known to oxidize to H+ ion while oxygen is being reduced O2-. Hence we can conclude that it is a redox reaction.

f) For the chemical reaction:

`NaOH\mleft(aq\mright)+HCl\mleft(aq\mright)\longrightarrow NaCl\mleft(aq\mright)+H_2O\mleft(aq\mright)`

This is not a redox reaction as well since there is no change in the oxidation number of the elements.