This is the complete reference for WACE Year 12 Chemistry. Built from analysis of recent SCSA marking keys.
Equilibrium and Le Chatelier
- K only changes with temperature. Catalysts, pressure, concentration shifts do not change K.
- For aA + bB ↔ cC + dD: K = [C]^c [D]^d / [A]^a [B]^b at equilibrium.
- Q vs K: if Q < K, forward reaction proceeds; if Q > K, reverse; if Q = K, equilibrium.
- Le Chatelier mark scheme phrasing: "the equilibrium shifts to the [side] in order to [reduce / counteract] the [perturbation]."
Acids and bases
| Formula | Use |
|---|
| pH = -log[H+] | For strong acids, [H+] = c |
| Kw = [H+][OH-] = 1.0 x 10^-14 (at 25 deg C) | Water autoionisation |
| pH + pOH = 14 | At 25 deg C |
| For weak acid HA: Ka = [H+][A-] / [HA] | Acid dissociation constant |
| For weak acid (Ka << c): [H+] = sqrt(Ka c) | Approximation; check Ka << c first |
| pKa = -log Ka | Smaller pKa = stronger acid |
| Henderson-Hasselbalch: pH = pKa + log([A-] / [HA]) | Buffer pH calculation |
Redox and electrochemistry
- OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain.
- Cell potential: E_cell = E_cathode - E_anode (both as reduction potentials).
- Sign convention: reverse a half-equation = reverse the sign of E.
- Faraday's constant: F = 96 500 C/mol e-.
- Quantitative electrolysis: n(e-) = It / F where I in amperes, t in seconds.
- Mark scheme: always state which species is oxidised, which is reduced, and the change in oxidation number.
Organic chemistry: functional groups
| Functional group | Formula | Suffix |
|---|
| Alkane | R-H | -ane |
| Alkene | R=R | -ene |
| Alkyne | R#R (triple bond) | -yne |
| Alcohol | R-OH | -ol |
| Aldehyde | R-CHO | -al |
| Ketone | R-CO-R | -one |
| Carboxylic acid | R-COOH | -oic acid |
| Ester | R-COOR | -yl -oate |
| Amine | R-NH2 (primary) | -amine |
| Amide | R-CONH2 | -amide |
Reactions and synthesis
- Addition (alkenes): alkene + H2/HX/H2O = saturated product.
- Substitution (alkanes): alkane + halogen + UV light = haloalkane + HX.
- Oxidation: alcohol -> aldehyde -> carboxylic acid (with strong oxidiser).
- Esterification: alcohol + carboxylic acid -> ester + water (acid catalyst).
- Yield: percentage yield = (actual / theoretical) x 100. Theoretical from limiting reagent.
Spectroscopy reference
| Technique | What it tells you |
|---|
| Mass spectrometry | Molecular weight from M+ peak; fragmentation pattern |
| Infrared (IR) | Functional group identification (peaks above 1500 cm^-1 most diagnostic) |
| Proton NMR (^1H) | Number of distinct H environments; integration = relative number of H |
| Carbon-13 NMR | Number of distinct C environments |
| Combustion analysis | Empirical formula from %C, %H, %O |
Common IR peaks (memorise)
- O-H (alcohol): 3200-3550 cm^-1, broad
- O-H (carboxylic acid): 2500-3300 cm^-1, very broad
- N-H (amine): 3300-3500 cm^-1
- C=O (carbonyl): 1680-1750 cm^-1, sharp
- C=C (alkene): 1620-1680 cm^-1
- C-H (sp^3): 2850-2960 cm^-1
Mark scheme phrasing markers reward
- Le Chatelier: "the equilibrium shifts to the [side] in order to reduce/counteract the [perturbation]."
- Acid-base: name the conjugate acid AND conjugate base.
- Redox: name the species oxidised, the species reduced, and the change in oxidation number.
- Organic: when explaining yield, name the limiting reagent before doing the calculation.
- Significant figures: 3 sig figs unless data given has fewer.
- Units: always include them on quantitative answers.
Useful constants
| Constant | Value |
|---|
| Avogadro's number Na | 6.022 x 10^23 /mol |
| Molar volume of gas at STP | 22.71 L/mol (or 24.79 L/mol at SLC) |
| Faraday's constant F | 96 500 C/mol e- |
| Universal gas constant R | 8.314 J / (mol K) |
Print and pin this
Print this page. Stick it in your Chemistry folder. Refer to it before every test and revision session. For the weekly cadence that builds chemistry into automatic recall, see our how to study Y12 Chemistry post. For the most common exam mistakes, see our top 10 Chemistry exam mistakes post.
If you want a Chemistry tutor who marks your past papers each week with the SCSA marking key, book a free trial class.
