IB DP Chemistry Topic 8.5 Acid deposition HL Paper 2

\({\text{C}}{{\text{a}}^{2 + }}\) and \({\text{NO}}_3^ – \);

electrostatic (attraction);

Do not accept ionic.

nitrogen/N and oxygen/O;

Do not accept nitrate/NO₃^–.

Accept atoms in nitrate/NO₃^–

pi/\(\underline \pi  \)-electrons shared by more than two atoms/nuclei / a pi/\(\underline \pi  \)-bond/overlapping p-orbitals that extends over more than two atoms/nuclei;

all (N–O) bonds equal length/strength/bond-order / charge on all oxygen/O atoms equal / increases stability/lowers PE (of the ion);

Accept a diagram that clearly shows one or both points.

produced by high temperature combustion;

Accept combustion/jet/car engines / car exhaust/emissions / lightning / action of bacteria/microorganisms.

Do not accept combustion/burning, cars, planes, jets, factories, power plants etc.

nitric acid/\({\text{HN}}{{\text{O}}_{\text{3}}}\) / nitrous acid/nitric(III) acid/\({\text{HN}}{{\text{O}}_{\text{2}}}\);

Accept “form acidic solutions / acid rain”.

acid deposition/rain / respiratory problems / corrosion problems / decomposition of ozone layer / photochemical smog / acidification/pollution of lakes / damage to plants/ trees;

Accept “acid rain” in either part (ii) or part (iii) but not both.

Do not accept air pollution.

It was distressing how many students taking HL Chemistry (over 50%?) do not know the formula of the nitrate ion! Many students also gave the type of bonding present between the ions, rather than the nature of the force asked for, though almost all could correctly identify the covalently bonded atoms. Hardly any could explain delocalization in terms of the overlap of p-orbitals, or the extension of a \(\pi \)-bond, over more than two atoms, though its effect on structure and stability were better known. In part (c), which tested Aim 8 of the syllabus, most managed to gain some of the marks available for atmospheric pollution from oxides of nitrogen. Inevitably, owing to some overlap in assessment statements these concepts would be more familiar to those studying the Environmental Chemistry option, but undoubtedly studying other options assists in other areas, such as organic chemistry.