Practical investigation into a substance (internal)
Internal 4 credits Titration Modification Method Reliability EvaluationAS 91910, 4 credits. A quantitative practical investigation — one of FOUR named titration types — to find how much of a substance is present in a consumer product. The standard's actual backbone is MODIFYING the sample or procedure based on a preliminary trial — not just running one clean titration.
1 Reading the notation
The backbone of every grade band is MODIFYING the sample or procedure — not just running a clean titration.📖 Terms the schedule grades you on
5 terms- Carry out (Achieved)
- A plan checking IF modification is needed; collect/process sufficient data; determine concentration; describe variable control.
- In-depth (Merit)
- Use a PRELIMINARY TRIAL to develop a valid MODIFICATION plan; quality data; accurate concentrations; explain variable control.
- Comprehensive (Excellence)
- Accurate concentration with sig figs/units; JUSTIFY the modification's effect on validity/accuracy; evaluate the outcome for the product.
- Quantitative analysis
- A titration procedure determining a substance's concentration — must be acid-base, complexometric, precipitation, or redox.
- Concentration determination
- Must use BOTH n = m/M and c = n/V, with stoichiometric principles.
2 The plan, the preliminary trial, and modification
A rough trial is not just for an approximate titre — it justifies a real change to sample or procedure. ✕Skipping the modification thread entirely
A well-run titration with concordant results but NO discussion of whether the sample needed diluting, or the procedure needed adjusting, based on a preliminary trial, has not evidenced the standard's actual Achieved/Merit/Excellence progression — however accurate the final number is.3 The calculation chain
Both n = m/M and c = n/V must appear, with correct scaling back to the original sample. Internal-style Vitamin C in a fruit drink by titration From titres to a labelled comparison. Discard the rough titre; average three concordant titres within 0.1 mL. n(titrant) = c × V using the AVERAGE titre in litres. Apply the mole ratio from the balanced equation to get n(vitamin C) in the aliquot. Scale from the aliquot to the whole sample — multiply by the dilution factor. Convert to mass (m = n × M) and then to mg per 100 mL to compare with the label. EVALUATE: state the percentage difference from the label, then say whether your calculated uncertainty is large enough to account for it. If it is not, a systematic error is implicated — name a candidate. ✓ Concordant titres, correct ratio, correct scaling, then an evaluation that connects uncertainty to discrepancy.4 Error, uncertainty, and evaluating the product outcome
The evaluation must connect back to what the result means for the actual consumer product.What makes an improvement suggestion score
- Names a SPECIFIC error, not a general one.
- Explains HOW it affected the result, and in which DIRECTION.
- Proposes a change that addresses that specific cause.
- For Excellence: connects the outcome back to the consumer product itself.
Practice
Recall it first, then use it — testing yourself builds the memory, where rereading the notes above only feels easier.
Recall and application shuffled together — you have to work out what each item wants before you can answer it, which is the part the exam actually tests. Both kinds feed the same spacing schedule, so anything you miss comes back sooner.
Say the answer out loud before flipping — that attempt is where the learning happens, even when you get it wrong.
Exam-style only. Instant feedback, shuffled each attempt, best score saved on this device.