How to answer HSC Chemistry short-answer questions

Eighty marks in 20 to 25 items. Calculations need every step and a unit; written parts follow the command word: describe gives features, explain adds cause and effect, and assess or evaluate ends with a judgement.

Marks	80, in 20 to 25 items
Longest items	At least two worth 7 to 9 marks
Often on	An investigation, a titration, data or a spectrum
Calculator	NESA-approved

Write to the marks

For a calculation, write each step with its formula, carry the units and give the answer to sensible significant figures.
For explain, give the point, tie it to the substance, conditions or data in the question, then say what it causes.
For assess and evaluate, weigh a strength and a limitation, then give a judgement and its reason.

Use the stimulus

Quote the numbers, the substances or the result in the question. An answer that could be written without reading the stimulus is rarely a full-marks answer.

Try 2 questions

Question 1

Three indicators: methyl orange changes from red to yellow between pH 3.1 and 4.4; bromothymol blue changes from yellow to blue between pH 6.0 and 7.6; phenolphthalein changes from colourless to pink between pH 8.3 and 10.0.
Indicator	pH range of colour change	Colour change as pH rises
methyl orange	3.1 to 4.4	red to yellow
bromothymol blue	6.0 to 7.6	yellow to blue
phenolphthalein	8.3 to 10.0	colourless to pink

Ethanoic acid is titrated with sodium hydroxide solution, and the equivalence point is at pH 8.7. Using the table, which indicator gives the most accurate end point?

Question 2

Absorbance of a standard solution of the iron complex at five wavelengths
Wavelength (nm)	Absorbance
420	0.21
470	0.48
510	0.66
560	0.39
620	0.08

A student will measure iron in tank water by colourimetry, using a coloured iron complex. She first measures the absorbance of one standard solution of the complex at five wavelengths (table). Which wavelength should she use for the analysis, and why?

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Questions people ask

How long should a 7 to 9 mark answer be?

Long enough to make each point, tie it to the question and develop it. Plan two or three linked points and a judgement rather than a list.