Summary & Quick Quiz റിഡോക്സ് പ്രവർത്തനങ്ങൾ
The whole chapter on one page: the story of redox reactions in five pictures, the ten key boxes of the textbook, every rule you need – conservation of mass, balancing, oxidation and reduction, oxidising and reducing agents, oxidation numbers – an oxidation-number calculator, the mistakes to avoid, flashcards, a scored quiz and your study checklist.
1. The chapter in five pictures
2. The key boxes of the textbook
In a chemical reaction the total mass of the reactants equals the total mass of the products. – page 3
Making the number of each kind of atom equal on both sides is balancing; the result is a balanced chemical equation. – page 4
The process in which electrons are lost in a chemical reaction: Na → Na+ + e−. – page 5
The substance that helps oxidation; it is itself reduced in the reaction (Cl2 in 2Na + Cl2 → 2NaCl). – page 6
The substance that helps reduction; it is itself oxidised (Na in 2Na + Cl2 → 2NaCl). – page 6
If all the bonds in a compound are taken as ionic, the charge on each atom is its oxidation number (oxidation state). – page 7
The sum of the oxidation numbers of the atoms in a compound is zero; in the elemental state the oxidation number is zero. – page 7
A reaction in which the oxidation number increases is oxidation; one in which it decreases is reduction. – page 8
Oxidation and reduction take place at the same time. In a redox reaction the oxidising agent is reduced and the reducing agent is oxidised. – page 8
1743–1794. Showed the role of oxygen in burning and in respiration, named oxygen and hydrogen, and classified elements into metals and non-metals. He lost his life in 1794 in the troubled years after the French Revolution. – page 3
States (s), (l), (g), (aq); the catalyst over the arrow; the energy change: N2(g) + 3H2(g) —Fe→ 2NH3(g) + heat. – page 4
3. Facts & rules
📐 Facts & rules card
oxidation = loss of e− = oxidation number ↑ · reduction = gain of e− = oxidation number ↓
oxidising agent → is reduced · reducing agent → is oxidised
Conservation of mass മാസ് സംരക്ഷണനിയമം · ആകെ മാസ്
| Equation | Reactants (u) | Products (u) |
|---|---|---|
| 2H2 + O2 → 2H2O | 4 u + 32 u = 36 u | 18 u + 18 u = 36 u |
| C + O2 → CO2 | 12 u + 32 u = 44 u | 44 u |
| CH4 + 2O2 → CO2 + 2H2O | 16 u + 2 × 32 u = 80 u | 44 u + 2 × 18 u = 80 u |
Masses in u (യൂണിഫൈഡ് അറ്റോമിക് മാസ് യൂണിറ്റ് (u)): H 1, C 12, N 14, O 16, Na 23, Mg 24, Al 27, S 32, Cl 35.5, Ca 40, Fe 56. When wood or paper burns, the mass only seems to fall because CO2 and water vapour escape; in a closed flask (balloon on the mouth) the balance reading does not change.
Balancing an equation രാസസമവാക്യ സമീകരണം
- Write the correct formulae of the reactants and products (H2, O2, Cl2, N2 are molecules).
- Count each kind of atom on both sides (a table helps: Tables 4.3–4.5).
- Change only the coefficients (the numbers in front) – never the subscripts.
- Start with an atom that is in only one substance on each side; leave free elements such as O2 or H2 to the end.
- Check every atom again: 4Al + 3O2 → 2Al2O3 (Al 4 = 4, O 6 = 6).
In an equation, ↑ means a gas is given off and ↓ a precipitate (അവക്ഷിപ്തം) forms; (s) solid, (l) liquid, (g) gas, (aq) in water.
Oxidation and reduction ഓക്സീകരണം · നിരോക്സീകരണം
Na → Na+ + e− · Al → Al3+ + 3e− · I− → I + e−
Cl + e− → Cl− · O + 2e− → O2− · Cu2+ + 2e− → Cu
Memory aid: “Loss Oxidation, Gain Reduction” – in English it is often remembered as OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons). Metals are generally oxidised; non-metals generally reduced.
| Oxidising agent ഓക്സീകാരി | Reducing agent നിരോക്സീകാരി | |
|---|---|---|
| What it does | helps the other substance to be oxidised (takes its electrons) | helps the other substance to be reduced (gives it electrons) |
| What happens to it | it is reduced – its oxidation number decreases | it is oxidised – its oxidation number increases |
| 2Na + Cl2 → 2NaCl | Cl2 | Na |
| 2Mg + O2 → 2MgO | O2 | Mg |
| Mg + 2HCl → MgCl2 + H2 | HCl | Mg |
Oxidation numbers ഓക്സിഡേഷൻ നമ്പർ
- An element in the elemental state (Na, Fe, H2, O2, Cl2, P4) → 0.
- In an ionic compound → the charge of the ion (MgO: Mg +2, O −2).
- In a covalent compound the shared electrons are counted with the more electronegative atom (HF: F −1, H +1).
- Use Table 4.7: H, Na, K +1 · Ca, Mg +2 · Al +3 · F, Cl, Br, I −1 · O −2.
- The sum in a compound is 0: write x for the unknown and multiply by the number of atoms – HNO3: (+1) + x + 3(−2) = 0 → x = +5.
The calculator uses the same rules as the textbook: Table 4.7 for the known atoms, then “sum = 0” for the last one.
Is it a redox reaction? റിഡോക്സ് പ്രവർത്തനങ്ങൾ
- Write the oxidation number above every atom on both sides.
- Find the element whose number goes up (oxidised) and the one whose number goes down (reduced).
- Both found → redox. The reactant containing the oxidised element is the reducing agent; the one containing the reduced element is the oxidising agent.
- No change at all (NaOH + HCl → NaCl + H2O; CaCO3 + 2HCl → CaCl2 + H2O + CO2) → not redox.
Redox in daily life: respiration (ശ്വസനം), burning of fuels (ജ്വലനം), decomposition of organic matter in oxygen (വിഘടനം), rusting and the oxide layer on metals (ഓക്സൈഡ് ആവരണം), and electricity from electrochemical cells (രാസവൈദ്യുത സെല്ലുകൾ).
- Changing subscripts to balance (H2O → H2O2). That makes a different substance – change only the coefficients.
- Saying mass is lost when wood burns. The gases (CO2, water vapour) escape; the total mass is conserved.
- Mixing up oxidation and reduction. Loss of electrons = oxidation; gain = reduction.
- Saying the oxidising agent is oxidised. It is reduced; the reducing agent is oxidised.
- Forgetting that free elements are 0. Na, Cl2, O2, H2 all have oxidation number 0.
- Forgetting to multiply by the number of atoms. K2Cr2O7: 2 × (+1) and 7 × (−2), and 2x for the two chromium atoms.
- Calling every reaction redox. Check for a change in oxidation number – neutralisation and CaCO3 + HCl are not redox.
- Writing the sign after the number (5+, 2−) for an oxidation number. Write +5, −2 (charges of ions are written 2+, 2−).
4. Flashcards
Click a card to flip it.
5. Scored quiz
Answer all sixteen, then press Check my answers. Each wrong answer shows the page to revise. For number answers type only the number (with a minus sign if it is negative).
6. Your study checklist
Ticks come from “Mark this page as completed” at the bottom of each page.
Next: the model test paper ▶ – attempt it on paper with a timer first, then check with the solved paper.