Chemistry
What this domain tests
Chemistry checks atomic structure, periodic trends, bonding and intermolecular forces, stoichiometry, solutions, acids and bases, redox, equilibrium, thermochemistry, and organic functional groups. Many IMAT items are quantitative; the chemistry is often simple once the mole relationship is set up.
Core rules
- Moles n = m/M; concentration c = n/V in litres; at standard conditions one mole of ideal gas occupies about 22.4 L, but use the value given.
- Balance equations before using mole ratios; the limiting reagent determines maximum product.
- Across a period, atomic radius decreases and electronegativity increases; down a group, radius increases and ionisation energy generally decreases.
- Ionic bonds transfer electrons; covalent bonds share them; hydrogen bonds are strong intermolecular attractions, not covalent bonds.
- A strong acid ionises completely; concentration and strength are different ideas.
- Oxidation is loss of electrons; reduction is gain.
Worked example
4.0 g of NaOH (M = 40 g/mol) is dissolved in water to make 500 mL of solution. Moles = 4.0/40 = 0.10 mol. Volume = 0.500 L. Concentration = 0.10/0.500 = 0.20 mol/L. If the question asked for pH, NaOH is a strong base, so [OH−] = 0.20 M, pOH = −log(0.20) ≈ 0.70, and pH ≈ 13.30 at 25 °C. Note that 500 mL is 0.5 L, not 5 L.
Traps that cost marks
Do not use mass instead of moles in a ratio. Do not call a concentrated weak acid “strong”. Check oxidation numbers by conservation of charge. In organic chemistry, distinguish aldehyde from ketone, alcohol from ether, and carboxylic acid from ester. In equilibrium, a catalyst changes rate, not the equilibrium position.