Chemistry

1. Oxidation - When things get "oxidized"

What is oxidation?

Your classical definition is spot on: oxidation is the addition of oxygen to a substance or the
removal of hydrogen from a substance. Let’s add a modern twist: oxidation also means the
loss of electrons. Think of it as a substance "giving away" electrons or teaming up with
oxygen, changing its form.

Examples of oxidation (mixing yours with some extras):

●​ Rusting of iron: You nailed it with 4Fe + 3O₂ → 2Fe₂O₃. Iron combines with oxygen
from the air to form rust. You see this on old cars, gates, or nails left outside—a slow
but steady oxidation process!
●​ Burning magnesium: Your example, 2Mg + O₂ → 2MgO, is perfect. That bright
white light comes from magnesium rapidly oxidizing into magnesium oxide. It’s like a
mini firework!
●​ Food getting spoiled: You’re right—when apple slices turn brown, oxygen in the air
oxidizes them. Lemon juice (an antioxidant) stops this by reacting with oxygen first.
●​ Combustion: Your example of methane, CH₄ + 2O₂ → CO₂ + 2H₂O, shows carbon
and hydrogen oxidizing. Another one: lighting a candle oxidizes wax, releasing heat
and light.
●​ Extra example - Statue of Liberty: The copper on the Statue of Liberty oxidized
over time, turning from shiny brown to green (copper oxide). That’s oxidation history
in action!

Real-life oxidation examples (yours plus more):

●​ Breathing: As you said, glucose oxidizes in our bodies to release energy—without it,
we’d be out of fuel!
●​ Cooking: You mentioned onions turning golden brown—oxidation gives them that
yummy flavor. Frying anything involves oxidation too!
●​ Photography: Old film relied on oxidation reactions, as you noted.
●​ Extra example - Fireworks: Those bright colors? Metals like strontium (red) and
copper (blue) oxidize fast to dazzle us!
2. Reduction - The flip side of oxidation
What is reduction?

You’ve got it: reduction is the removal of oxygen from a substance or the addition of
hydrogen to a substance. Let’s add that it’s also the gain of electrons. It’s like a substance
"taking back" electrons or shedding oxygen to simplify itself.

Examples of reduction (yours with some bonuses):

●​ Extraction of iron from its ore: Your example, Fe₂O₃ + 3CO → 2Fe + 3CO₂, shows
iron oxide losing oxygen to become pure iron in blast furnaces—key for steel!
●​ Reduction of copper oxide: You said CuO + H₂ → Cu + H₂O, turning black copper
oxide into shiny copper. A classic lab demo!
●​ Hydrogenation of oils: You’re spot on with liquid oils turning into solid fats like
margarine by adding hydrogen. Think of it as oil getting a hydrogen hug!
●​ Extra example - Photosynthesis: Plants reduce CO₂ to glucose (C₆H₁₂O₆) using
sunlight, essentially adding hydrogen in a way.

Real-life reduction examples (yours and more):

●​ Making steel: You mentioned iron ore being reduced to iron—yep, that’s how we get
strong steel!
●​ Food industry: You noted hydrogenation for margarine. It’s also used for smooth
peanut butter!
●​ Photography: Silver compounds reduce to form images, as you said.
●​ Extra example - Electroplating: Shiny chrome on bikes comes from reducing metal
ions to coat surfaces.

3. Oxidation State (Oxidation Number) - Tracking the

"charge score"
What is oxidation state?

You described it perfectly—it’s like a "charge score" showing how many electrons an atom
has gained or lost in a compound. It’s a handy way to track changes in reactions.

Rules to find oxidation state (your list is ace, here it is again):

1.​ Free elements (e.g., O₂, H₂): 0

2.​ Hydrogen: Usually +1 (except in metal hydrides like NaH, where it’s -1)
3.​ Oxygen: Usually -2 (except in peroxides like H₂O₂, where it’s -1)
4.​ Group 1 metals (e.g., Na, K): +1
5.​ Group 2 metals (e.g., Mg, Ca): +2
 6.​ Sum in a compound: 0
7.​ Sum in an ion: Equals the ion’s charge

Examples of finding oxidation states (yours plus extras):

●​ Water (H₂O): You said H = +1, O = -2. Check: 2(+1) + (-2) = 0. Perfect!
●​ Sulfuric acid (H₂SO₄): You calculated H = +1 (so 2H = +2), O = -2 (so 4O = -8). Then
+2 + S - 8 = 0, so S = +6. Spot on!
●​ Potassium permanganate (KMnO₄): You got K = +1, 4O = -8, so +1 + Mn - 8 = 0,
Mn = +7. Awesome!
●​ Extra example - Carbon dioxide (CO₂): O = -2, so 2(-2) = -4. Total = 0, so C = +4.
●​ Extra example - Ammonia (NH₃): H = +1, so 3(+1) = +3. Total = 0, so N = -3.

Why it matters:

Oxidation states show if an atom is oxidized (number goes up) or reduced (number goes
down). Like carbon: -4 in CH₄, +4 in CO₂—that’s oxidation!

4. Redox Reactions - Teamwork time!

What are redox reactions?

You said it: REDuction + OXidation = REDOX. It’s when one substance oxidizes (loses
electrons) and another reduces (gains electrons) at the same time. A chemical dance!

Modern definitions (you’ve got these down):

●​ Oxidation: Loss of electrons (OIL - Oxidation Is Loss)

●​ Reduction: Gain of electrons (RIG - Reduction Is Gain)

Examples of redox reactions (yours with extras):

●​ Zinc + Copper sulfate: You wrote Zn + CuSO₄ → ZnSO₄ + Cu. Zn → Zn²⁺ (oxidized,
loses 2e⁻), Cu²⁺ → Cu (reduced, gains 2e⁻). Zn reduces Cu²⁺, Cu²⁺ oxidizes Zn.
●​ Hydrogen + Chlorine: You gave H₂ + Cl₂ → 2HCl. H₂ (0) → H⁺ (+1, oxidized), Cl₂ (0)
→ Cl⁻ (-1, reduced).
●​ Photosynthesis: You noted 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. CO₂ reduces to glucose,
H₂O oxidizes to O₂—plants rock redox!
●​ Extra example - Burning coal: C + O₂ → CO₂. Carbon (0) oxidizes to +4, oxygen (0)
reduces to -2.
●​ Extra example - Bleach: Chlorine bleach oxidizes stains (loses color), while chlorine
reduces.
Real-life redox examples (yours plus more):

●​ Battery functioning: You’re right—chemical redox powers your phone!

●​ Digestion: Food oxidizes for energy, as you said.
●​ Bleaching: Chlorine’s redox magic, like you noted.
●​ Extra example - Rust prevention: Those "Do not eat" packets in shoe boxes absorb
oxygen to stop oxidation.

5. Disproportionation Reaction - One element, two

fates!
What is a disproportionation reaction?

You’ve got it: it’s a redox reaction where the same element is both oxidized and reduced. It
starts with one oxidation state and splits into two different ones.

Key point (you nailed it):

The element goes from one oxidation state to a higher one (oxidized) and a lower one
(reduced).

Examples of disproportionation (yours with extras):

●​ Chlorine in cold alkali: You wrote Cl₂ + 2NaOH → NaCl + NaClO + H₂O. Cl₂ (0) →
Cl⁻ (-1, reduced) and ClO⁻ (+1, oxidized).
●​ Hydrogen peroxide decomposition: You said 2H₂O₂ → 2H₂O + O₂. O in H₂O₂ (-1) →
H₂O (-2, reduced) and O₂ (0, oxidized).
●​ Phosphorus in hot alkali: You gave 4P + 3NaOH + 3H₂O → 3NaH₂PO₂ + PH₃. P (0)
→ +1 (oxidized) and -3 (reduced).
●​ Extra example - Copper(I) chloride: 2CuCl → Cu + CuCl₂. Cu⁺ (+1) → Cu (0,
reduced) and Cu²⁺ (+2, oxidized).

Real-life disproportionation examples (yours and more):

●​ Bleaching powder production: You mentioned Cl₂ in lime water—disproportionation

makes it happen!
●​ Hydrogen peroxide: You’re right—it decomposes slowly, hence dark bottles.
●​ Photography: Some solutions use disproportionation, as you noted.
●​ Extra example - Sodium thiosulfate: Used in photography to fix images via
disproportionation.
Memory Tips (Yours are great, here’s a boost):
●​ Oxidation vs. Reduction: You’ve got OILRIG and LEO says GER—perfect!
Another: think of a lion—LEO (Loss = Oxidation), GER (Gain = Reduction).
●​ Agents: You said oxidizing agents get reduced, reducing agents get oxidized.
Imagine the oxidizing agent as a thief (steals electrons), reducing agent as a giver.
●​ Disproportionation: Your "one element, two destinies" rocks! Picture a superhero
splitting into a stronger and weaker version.

Practice Questions (Let’s solve them with your notes!):

1.​ Identify oxidation and reduction in: Mg + CuO → MgO + Cu
○​ Mg (0) → Mg²⁺ (+2, loses electrons = oxidized).
○​ Cu (+2 in CuO) → Cu (0, gains electrons = reduced).
○​ Mg is oxidized, CuO is reduced.
2.​ Find oxidation state of Cr in K₂Cr₂O₇
○​ K = +1, so 2K = +2.
○​ O = -2, so 7O = -14.
○​ Let Cr = x, with 2 Cr: 2x.
○​ Total: +2 + 2x - 14 = 0 → 2x = 12 → x = +6.
○​ Cr = +6.
3.​ Is this disproportionation? 3Cl₂ + 6KOH → 5KCl + KClO₃ + 3H₂O
○​ Cl₂ (0) → Cl⁻ in KCl (-1, reduced).
○​ Cl in KClO₃ (+5, oxidized).
○​ Same Cl goes from 0 to -1 and +5—yes, disproportionation!
4.​ Why does iron rust faster in salty water?
○​ Salt (like NaCl) conducts electricity, speeding up the redox reaction of rusting
(Fe → Fe₂O₃). More electrons move faster!
5.​ Explain why lemon juice prevents apple browning.
○​ You said it’s an antioxidant—yep! Vitamin C in lemon juice reacts with oxygen
before it can oxidize the apple, keeping it fresh.