Which of the following equations does not represent an oxidation-reduction reaction?
3Al + 6HCl → 3H2 + AlCl3
2NaCl + Pb(NO3)2 → PbCl2 + 2NaNO3
2H2O → 2H2 + O2
2NaI + Br2 → 2NaBr + I2
Cu(NO3)2 + Zn → Zn(NO3)2 + Cu
The equation that does not represent an oxidation-reduction reaction is:
2H2O → 2H2 + O2
This equation is a decomposition reaction where water molecules are broken down into hydrogen gas and oxygen gas. There is no exchange of electrons between different elements in this reaction, which is characteristic of oxidation-reduction reactions.
To determine which equation does not represent an oxidation-reduction (redox) reaction, we need to check if there is a change in the oxidation states of the elements involved in the reaction.
In a redox reaction, some elements undergo a change in oxidation state, indicating a transfer of electrons. The element that is oxidized loses electrons and the element that is reduced gains electrons.
Let's analyze each equation:
1. 3Al + 6HCl → 3H2 + AlCl3
In this equation, aluminum (Al) is oxidized from an oxidation state of 0 to +3, while hydrogen (H) is reduced from an oxidation state of +1 to 0. This is a redox reaction.
2. 2NaCl + Pb(NO3)2 → PbCl2 + 2NaNO3
In this equation, sodium (Na) remains in an oxidation state of +1 before and after the reaction. Nitrogen (N), lead (Pb), and chlorine (Cl) also maintain their oxidation states. This is not a redox reaction.
3. 2H2O → 2H2 + O2
In this equation, hydrogen (H) goes from an oxidation state of +1 in water (H2O) to 0 in hydrogen gas (H2), while oxygen (O) goes from -2 in water to 0 in oxygen gas (O2). This is a redox reaction.
4. 2NaI + Br2 → 2NaBr + I2
In this equation, iodine (I) changes its oxidation state from -1 in sodium iodide (NaI) to 0 in iodine (I2), and bromine (Br) goes from 0 in its diatomic form to -1 in sodium bromide (NaBr). This is a redox reaction.
5. Cu(NO3)2 + Zn → Zn(NO3)2 + Cu
In this equation, copper (Cu) remains in an oxidation state of +2 before and after the reaction, and zinc (Zn) also retains its oxidation state of 0. This is not a redox reaction.
Therefore, equation 2 (2NaCl + Pb(NO3)2 → PbCl2 + 2NaNO3) does not represent an oxidation-reduction reaction, as there is no change in oxidation states for any of the elements involved.
You need to learn how to determine this. Here is a set of rules that will allow you to determine the oxidation state of each element in each equation. Then you can answer the question.
http://www.chemteam.info/Redox/Redox-Rules.html