IB Chemistry HL flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

VSEPR domain count

Number of electron domains (bonding regions plus lone pairs) around a central atom. Four domains give tetrahedral geometry; lone pairs reduce bond angles below the ideal value.

Hybridisation and geometry

Two domains give sp hybridisation and linear 180° geometry; three give sp2 and trigonal planar 120°; four give sp3 and tetrahedral 109.5°.

Formal charge formula

Formal charge equals valence electrons minus non-bonding electrons minus half the bonding electrons. Structures with formal charges nearest zero are preferred resonance contributors.

Molecular polarity test

A molecule is polar only if it contains polar bonds and the bond dipoles fail to cancel by symmetry. Carbon dioxide is non-polar; water is polar.

First ionisation energy trend

First ionisation energy generally rises across a period and falls down a group. Dips occur at group 13 and group 16 because of p-orbital occupancy and electron pairing.

Transition metal electron configuration

Chromium is [Ar]3d5 4s1 and copper is [Ar]3d10 4s1. Cations lose 4s electrons first, so Fe2+ is [Ar]3d6.

Hydrogen bonding criteria

Hydrogen bonding requires H bonded to N, O or F and a lone pair on a nearby N, O or F. It raises boiling points sharply compared with similar molar masses.

Lattice enthalpy dependence

Lattice enthalpy magnitude increases with higher ionic charges and smaller ionic radii. Magnesium oxide therefore has a far larger lattice enthalpy than sodium chloride.

Rate law determination

Rate law must be found experimentally, not from stoichiometry. Initial-rate comparison or half-life constancy identifies the order with respect to each reactant.

Arrhenius plot

Plotting ln k against 1/T gives a straight line of slope −Ea/R and intercept ln A, allowing activation energy to be extracted from rate data.

Rate-determining step

The slowest step in a mechanism controls the overall rate, and its reactants appear in the rate law. Fast reversible preceding steps require a pre-equilibrium approximation.

Equilibrium constant K

Kc excludes pure solids and liquids. K changes only with temperature; catalysts and pressure changes at constant temperature leave K unchanged.

Reaction quotient Q

Q has the same form as K but uses current concentrations. If Q is less than K the reaction proceeds forward; if greater, it proceeds in reverse.

Gibbs energy and K

ΔG° equals −RT ln K and also −nFE°cell. A negative ΔG° corresponds to K greater than one and a spontaneous reaction under standard conditions.

Buffer pH equation

pH equals pKa plus log of the ratio of conjugate base concentration to weak acid concentration. Buffer capacity is greatest when the two concentrations are equal.

Electrode potential convention

E°cell equals E°cathode minus E°anode, using reduction potentials. Oxidation occurs at the anode, which is the negative electrode in a voltaic cell.

Uncertainty propagation rules

For addition and subtraction, add absolute uncertainties. For multiplication and division, add percentage uncertainties. Quote final uncertainty to one significant figure.

Burette reading uncertainty

Each burette reading carries an uncertainty of about plus or minus 0.05 cm3. A titre uses two readings, so the delivered volume uncertainty is about 0.1 cm3.

Random versus systematic error

Random error scatters results and is reduced by averaging repeats. Systematic error shifts all results in one direction and is not removed by averaging.

IA assessment criteria

Internal assessment is marked on research question, background, methodology, data collection and processing, analysis, evaluation, and communication, each against explicit descriptors.

Calorimetry equation

Heat released equals mass times specific heat capacity times temperature change. For aqueous solutions use 4.18 J g−1 K−1 and extrapolate cooling curves to correct heat loss.

Line of best fit gradient

Gradient uncertainty is estimated from the steepest and shallowest acceptable lines through the data, giving a range that reflects scatter.

Option A polymer types

Addition polymers form by chain growth of unsaturated monomers with no by-product. Condensation polymers form by step growth with elimination of a small molecule such as water.

Option B zwitterion

At the isoelectric point an amino acid exists as a zwitterion with both positive and negative charges, giving zero net charge and minimum solubility.

Option B enzyme inhibition

A competitive inhibitor raises apparent Km while Vmax is unchanged. A non-competitive inhibitor lowers Vmax because it binds away from the active site.

Option C energy density

Energy density is the energy released per unit mass or volume of fuel on complete combustion under standard conditions, allowing fair comparison between fuels.

Option D therapeutic index

Therapeutic index equals toxic dose divided by therapeutic dose. A higher index indicates a wider safety margin between effective and harmful doses.

Option D aspirin synthesis

Aspirin is made by esterifying salicylic acid with ethanoic anhydride. Purity is checked by melting point comparison and thin-layer chromatography.

Variables in an investigation

The independent variable is deliberately changed, the dependent variable is measured, and controlled variables are held constant and reported to ensure a fair test.

Reliability versus validity

Reliability means consistent results on repeating a measurement. Validity means the measurement actually addresses the research question and controls relevant variables.

Falsifiable hypothesis

A hypothesis must be testable and capable of being disproved by observation. Predictions derived from it must be specific and measurable.

Extrapolation caution

Conclusions should be limited to the range of data collected. Predicting beyond measured values requires a theoretical model and adds unquantified uncertainty.