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Applying chemical ideas review
A summary of all of Module 8 Applying Chemical Ideas, how the topics connect, key words, and a mixed HSC-style test covering ion tests, gravimetric and titration analysis, AAS and colorimetry, functional group tests, spectroscopy and chemical synthesis.
Use this page to check the whole module. Read the summary, make sure you can explain every key word, then do the test under exam conditions before checking any answers.
Module summary
| Topic | What you need to know |
|---|---|
| 8A Monitoring the environment | Why water, soil and air are monitored; sources and effects of heavy metals, nutrients and acid mine drainage; bio-magnification; units mg/L, ppm and ppb; comparing results with guideline values. |
| 8B Identifying cations | Flame colours (Ba²⁺ pale green, Ca²⁺ brick red, Cu²⁺ blue-green); precipitates with Cl⁻, SO₄²⁻, OH⁻ and I⁻; complexes [FeSCN]²⁺ and [Cu(NH₃)₄]²⁺; a logical order of tests; net ionic equations. |
| 8C Identifying anions | CO₃²⁻ fizzes with acid; SO₄²⁻ gives BaSO₄ in acid; PO₄³⁻ gives a Ba²⁺ precipitate that dissolves in acid; halides give AgCl/AgBr/AgI confirmed with NH₃; acidify with HNO₃ first and use nitrate reagents. |
| 8D Gravimetric analysis and precipitation titrations | Precipitate, filter, wash, dry to constant mass, weigh, then mass → moles → percentage. Mohr titration: Ag⁺ + Cl⁻ with chromate indicator. Which errors make results high or low. |
| 8E Colorimetry, UV-vis and AAS | A = εlc; measure at the complementary colour or λmax; AAS uses a hollow cathode lamp of the same element (Walsh, CSIRO); calibration curves, blanks, interpolation and dilution factors. |
| 8F Functional group tests | Bromine water for C=C and C≡C; dichromate for 1° and 2° alcohols; carbonate for carboxylic acids; sodium and esterification for –OH. |
| 8G Mass spectrometry | Ionise, accelerate, separate by m/z, detect. Molecular ion gives molar mass; base peak is the most abundant ion; losses of 15, 17, 29 and 45; Cl gives 3 : 1 and Br 1 : 1 M and M + 2 peaks. |
| 8H Infrared spectroscopy | Bonds absorb IR matching their vibration if the dipole changes. Broad O–H 3230–3550 (alcohol); very broad O–H 2500–3000 (acid); sharp C=O 1680–1750; fingerprint region below 1500. |
| 8I NMR spectroscopy | Chemical shift from TMS; ¹³C counts carbon environments; ¹H gives environments, integration and splitting by the n + 1 rule. |
| 8J Identifying an unknown | % composition → empirical formula; M⁺ → molecular formula; IR → functional groups; NMR → connectivity; check one structure fits everything. |
| 8K Planning a synthesis | Reagents, conditions, yield and purity; limiting reagent and percentage yield; step yields multiply; purification and melting point checks. |
| 8L Industry and sustainability | Rate, yield, cost, safety, environment and social factors; Haber process compromises; green chemistry and atom economy; fermentation vs hydration of ethene; PLA. |
Putting it together
The whole module answers three questions a working chemist is asked every day: what is in this sample, how much is there, and how can we make it? The inorganic tests (8B, 8C) use the solubility and complex-ion chemistry of Module 5 to say what; gravimetric analysis, titrations and AAS (8D, 8E) use the stoichiometry of Modules 5 and 6 to say how much, which is what environmental monitoring (8A) depends on. The organic methods (8F to 8J) turn the functional groups of Module 7 into evidence: chemical tests and IR show which groups are there, mass spectrometry gives the size of the molecule, and NMR shows how its atoms are connected. Synthesis and design (8K, 8L) then uses equilibrium (Module 5), reaction rates and organic reactions to make products efficiently, safely and sustainably.
Key words
absorbance · atom economy · atomic absorption spectroscopy · base peak · Beer–Lambert law · bio-magnification · blank · calibration curve · carbon-13 NMR · chemical shift · colorimetry · complex ion · constant mass · deshielding · E-factor · end point · equivalent environments · extrapolation · fingerprint region · flame test · fragment · functional group · gravimetric analysis · green chemistry · hollow cathode lamp · infrared spectroscopy · integration · interpolation · limiting reagent · mass spectrometry · Mohr method · molecular ion · m/z · net ionic equation · n + 1 rule · percentage yield · precipitation titration · proton NMR · qualitative · quantitative · recrystallisation · spectator ion · splitting · tetramethylsilane · theoretical yield · UV-visible spectrophotometry · wavenumber
Test yourself
A colourless solution gives a white precipitate with dilute HCl. The precipitate dissolves in dilute ammonia. The cation present is
AgCl dissolves in dilute NH₃ as [Ag(NH₃)₂]⁺. PbCl₂ would dissolve in hot water instead.
0.512 g of a chloride salt is dissolved and treated with excess AgNO₃, giving 1.148 g of dry AgCl (M = 143.4). The percentage of chloride in the salt is
n(AgCl) = 1.148 ÷ 143.4 = 8.006 × 10⁻³ mol; m(Cl) = 8.006 × 10⁻³ × 35.45 = 0.2838 g; 0.2838 ÷ 0.512 × 100 = 55.4%.
Why is atomic absorption spectroscopy selective for one element?
Each element's hollow cathode lamp produces lines that match that element's own absorption lines.
A compound has a strong IR absorption at 1740 cm⁻¹, no broad absorption above 3000 cm⁻¹, and its ¹H NMR spectrum shows a 3H singlet at 2.0 ppm, a 2H quartet at 4.1 ppm and a 3H triplet at 1.3 ppm. It is
An ester (C=O, no O–H). The O–CH₂ quartet at 4.1 ppm and CH₃–C=O singlet at 2.0 ppm fit CH₃COOCH₂CH₃.
How many signals are in the ¹³C NMR spectrum of 2-methylpropan-2-ol, (CH₃)₃COH?
The three CH₃ carbons are equivalent; the central C–OH carbon is different.
The mass spectrum of a compound has peaks at m/z 78 and 80 in a 3 : 1 ratio. The compound could be
3 : 1 means one Cl atom. C₃H₇³⁵Cl has M = 78.
Which statement about the synthesis of ammonia by the Haber process is correct?
The other statements are false: a catalyst doesn't shift equilibrium, the reaction is exothermic, and high pressure favours ammonia.
Name each technique or idea in the module overview.
Which part of Module 8 does each idea belong to?
Put the steps for identifying an unknown organic compound in a sensible order.
Silver iodide is a precipitate. In AAS, light is by ground-state atoms. Readings above the highest standard require the sample to be . The overall yield of a multi-step synthesis is the of the step yields. In ¹H NMR, a CH₃ next to a CH₂ appears as a .
A council suspects that run-off from an old mine is polluting a creek with copper and sulfate. Describe how a chemist could (a) confirm that Cu²⁺ and SO₄²⁻ are present and (b) measure the concentration of each. Justify your choice of methods, and include relevant equations.
(a) Confirming the ions. Add a few drops of sodium hydroxide to a sample: a pale blue precipitate shows Cu²⁺, $\text{Cu}^{2+}(aq) + 2\text{OH}^-(aq) \rightarrow \text{Cu(OH)}_2(s)$; it dissolves in excess ammonia to give deep blue [Cu(NH₃)₄]²⁺, confirming copper. To a fresh sample add dilute nitric acid (to remove any carbonate, which would also precipitate with barium), then barium nitrate: a white precipitate that doesn't dissolve in the acid shows sulfate, $\text{Ba}^{2+}(aq) + \text{SO}_4^{2-}(aq) \rightarrow \text{BaSO}_4(s)$.
(b) Copper by AAS. Copper may be present at only a few mg/L, so a sensitive and selective method is needed. Prepare copper standards (for example 0–5 mg/L) and a blank, fit a copper hollow cathode lamp (324.8 nm), measure the standards and plot a calibration curve. Measure the filtered creek sample, diluting by a known factor if it reads above the highest standard, then read off the concentration and multiply by the dilution factor. Because the lamp emits only lines that copper atoms absorb, iron and other metals in the run-off don't interfere.
(b) Sulfate by gravimetric analysis. Mine run-off is often high in sulfate, so a precise gravimetric method works well. Take a measured volume (for example 250.0 mL), acidify and heat it, add excess barium chloride, and check that precipitation is complete. Filter, wash with warm water, dry to constant mass and weigh the BaSO₄. Then $n(\text{SO}_4^{2-}) = m \div 233.4$ and the concentration is this amount × 96.07 g/mol ÷ the volume in litres.
Both results would then be compared with the water-quality guideline values to decide whether the creek is polluted.