Unit 2: How do chemical reactions shape the natural world?
13 dot points across 3 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.
How do substances interact with water?
- the reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates (and hydrogen carbonates), including the writing of balanced equations and an explanation of the underlying acid-base or redox process
A focused VCE Chemistry Unit 2 answer on the four classic acid reactions. Covers acid plus metal (redox, hydrogen gas), acid plus metal oxide (neutralisation, salt and water), acid plus metal hydroxide (neutralisation, salt and water) and acid plus carbonate or hydrogen carbonate (salt, water and carbon dioxide), with balanced equations and the underlying mechanisms.
7 min answer → - the writing of balanced full, ionic and net ionic equations for reactions in aqueous solution including precipitation, neutralisation and metal displacement reactions, with state symbols
A focused VCE Chemistry Unit 2 answer on writing balanced full, ionic and net ionic equations for aqueous reactions. Covers precipitation, neutralisation and metal displacement reactions, the rules for splitting (aq) species, the role of spectator ions, and consistent use of state symbols.
7 min answer → - the relative reactivity of metals as shown in the activity series, the prediction of metal displacement reactions in aqueous solution, and the relationship between metal reactivity and reactions with water, acids and oxygen
A focused VCE Chemistry Unit 2 answer on the metal reactivity series and displacement reactions in aqueous solution. Covers the ordering of common metals, the prediction of whether a displacement will occur, the half-equations for the redox process, and the reactions of metals with water, acids and oxygen.
8 min answer → - the polar nature of the water molecule, the intermolecular forces (hydrogen bonding, dipole-dipole and dispersion) that operate between water molecules and between water and solute particles, and the use of these forces to predict relative solubility of substances in water
A focused VCE Chemistry Unit 2 answer on water polarity and intermolecular forces in aqueous solutions. Covers the bent shape and dipole of water, hydrogen bonding versus dipole-dipole versus dispersion forces, the like-dissolves-like rule, and how to rank the relative solubility of polar, ionic and non-polar substances in water.
7 min answer → - the application of stoichiometric calculations to reactions in aqueous solution, including the use of n = cV and balanced equations to determine limiting reagent, mass or concentration of reactants and products, and percentage yield where appropriate
A focused VCE Chemistry Unit 2 answer on the stoichiometry of aqueous reactions. Covers the use of n = cV with concentration in mol per litre, the limiting-reagent decision, the calculation of mass or concentration of products from a balanced equation, and percentage yield in a solution context.
7 min answer → - the distinction between strong and weak acids and bases using the extent of ionisation, the acid ionisation constant Ka and base ionisation constant Kb, and the relationship between the strength of an acid and the strength of its conjugate base
A focused VCE Chemistry Unit 2 answer on the strength of acids and bases. Covers the extent of ionisation as the defining criterion for strong vs weak, the ionisation constants Ka and Kb, how to compare strengths using pKa and pKb, and the inverse relationship between an acid and its conjugate base.
8 min answer →
How do chemicals interact with water?
- expressing the concentration of solutions (mol L^-1, g L^-1, %m/v, %m/m, %v/v and ppm) including dilution calculations, and the Brønsted-Lowry model of acids and bases including conjugate acid-base pairs, the distinction between strong and weak (and concentrated and dilute) acids and bases, and the calculation of pH from [H+]
A focused VCE Chemistry Unit 2 answer on concentration and acid-base chemistry. Covers concentration units (mol L^-1, g L^-1, %m/v, %m/m, %v/v, ppm) and dilution calculations, the Brønsted-Lowry model with conjugate acid-base pairs, strong vs weak and concentrated vs dilute, and the calculation of pH from [H+].
9 min answer → - redox reactions in aqueous solution including the assignment of oxidation numbers, identification of the species oxidised and reduced, and the construction and balancing of half-equations and overall ionic equations in acidic solution
A focused VCE Chemistry Unit 2 answer on redox in aqueous solution. Covers the rules for assigning oxidation numbers, identification of oxidant and reductant, the half-equation balancing procedure in acidic solution (electrons, then H2O for O, then H+ for H), and combining half-equations into a balanced overall ionic equation.
9 min answer → - the explanation of the properties of water (including high boiling point, high specific heat capacity, surface tension and the density of ice relative to liquid water) and the role of water as a solvent for polar and ionic substances, including the use of solubility rules to predict precipitation reactions and write ionic equations
A focused VCE Chemistry Unit 2 answer on the chemistry of water. Covers hydrogen bonding and how it explains water's anomalous physical properties, how water dissolves ionic and polar molecular substances, the use of solubility rules to predict precipitation, and writing balanced ionic and net ionic equations.
9 min answer →
How are substances in water measured and analysed?
- the principles and stoichiometry of gravimetric analysis to determine the concentration or percentage by mass of an analyte in a sample, including precipitation, filtration, washing, drying to constant mass, and the calculation of the analyte from the mass of the precipitate
A focused VCE Chemistry Unit 2 answer on gravimetric analysis. Covers the choice of precipitating reagent, the lab steps (precipitation, filtration, washing, drying to constant mass), the stoichiometric calculation from precipitate mass to analyte amount, and the common sources of error in a gravimetric determination.
8 min answer → - the principles and use of colorimetry and UV-visible spectroscopy (including the Beer-Lambert relationship) and atomic absorption spectroscopy (AAS), and the use of calibration curves to determine the concentration of an analyte in water
A focused VCE Chemistry Unit 2 answer on instrumental analysis. Covers the principles of colorimetry and UV-visible spectroscopy with the Beer-Lambert relationship, the use of calibration curves, and atomic absorption spectroscopy (AAS) for trace-metal analysis, with a comparison of techniques.
8 min answer → - the principles of volumetric analysis including acid-base and redox titrations, the use of primary and secondary standard solutions and indicators, and stoichiometric calculations including back-titration to determine the concentration or amount of analyte
A focused VCE Chemistry Unit 2 answer on volumetric analysis. Covers acid-base and redox titrations, primary and secondary standards, the choice of indicator from titration curves, the c1V1 / c2V2 / mole-ratio workflow, and back-titration for samples that react slowly or with excess.
9 min answer → - the selection and use of appropriate analytical techniques (gravimetric analysis, volumetric analysis, colorimetry, UV-visible spectroscopy and atomic absorption spectroscopy) to determine the concentration of analytes in a water sample, including comparing the suitability of techniques for major and trace analytes
A focused VCE Chemistry Unit 2 answer on choosing analytical techniques for water-quality testing. Compares gravimetric analysis, volumetric analysis (titration), colorimetry, UV-visible spectroscopy and atomic absorption spectroscopy on the basis of detection limit, accuracy, cost, sample type and analyte concentration.
7 min answer →