Question

Option 1:  Shane is doing redox reactions.  He discovers that all of the combustion reactions involving oxygen are redox, and all of the single replacement reactions are redox.  He also realizes the pattern that none of the double replacement reactions are redox.  The only problem is, he’s not sure why these patterns are happening.

Explain to him why all combustion reactions are redox.  Which entity will be oxidized and which will be reduced?

Explain to him why all single replacements are redox.  If the cations are exchanged which entity is oxidized and which is reduced (the metal in elemental form on the reactant side, and the metal in a compound on the reactant side).  

In a single replacement if the anions exchange, which entity is oxidized and which is reduced? (The nonmetal in elemental form on the reactant side and the nonmetal in a compound on the reactant side)

Why are the double replacements never redox?

Will all decomposition reactions be categorized as all redox/ none redox?  Why or why not?

Option 2:  Louie is confused about balancing equations.  He turns to Google and YouTube and watches several videos until the ideas finally start making sense.  Find and watch three videos online about balancing equations.  Copy and post the links into your post.  After each link include a summary of what they taught and what you found helpful about each video.  Then post 3 unbalanced equations.  Walk through how to balance 2 and leave the third for other students to try to balance.

Option 3:Carrie is struggling with balancing equations. She decides to make the molecules using the toothpicks and gumdrops as she did before (a nice review of the geometry) and then balance the equation, making sure that she has the same number of each type of atom on each side of the equation using her toothpicks and gumdrops as she did before. Do the same and then take the pictures and post them.

The reactions to figure out are:

Hydrogen and Oxygen combine to make water.

Nitrogen dioxide reacts to become Dinitrogen tetroxide.

Aluminum and oxygen combine to make aluminum oxide.

Answer 1

Question 1.

(i) In all the combustion reactions, oxygen undergoes reduction, whereas the component under combustion undergoes oxidation.

Example: CH₄ + 2O₂ CO₂ + 2H₂O(g)

Oxidation state of C in CH4 = -4 and that in CO2 = +4. Hence, C undergoes oxidation from -4 to +4.

Oxidation state of O in O2 = 0 and that in H₂O & CO₂ = -2. Hence, O undergoes reduction from 0 to -2.

So, in a combustion reaction, both oxidation and reduction take place.

Hence, all the combustion reactions are redox reactions.

(ii) Single replacement reactions: Cation exchange

Na(s) + HCl(aq) NaCl(aq) + 1/2H₂(g)

Oxidation state of Na in Na(s) = 0 and that in NaCl= +1. Hence, 'Na' undergoes oxidation from 0 to +1.

Oxidation state of H in HCl = +1 and that in H₂ = 0. Hence, 'H' undergoes reduction from +1 to 0.

Hence, all the single replacement reactions involving cation exchange are redox reactions.

(iii) Single replacement reactions: Anion exchange

Cl₂(g) + 2NaBr(aq) 2NaCl(aq) + Br₂(g)

Oxidation state of Cl in Cl₂ = 0 and that in NaCl= -1. Hence, 'Cl' undergoes reduction from 0 to -1.

Oxidation state of Br in NaBr = -1 and that in Br₂ = 0. Hence, 'Br' undergoes oxidation from -1 to 0.

Hence, all the single replacement reactions involving anion exchange are redox reactions.