What the investigation does
The essay compares five levels of sodium borohydride excess, from 0% to 100%, in the reduction of vanillin to vanillyl alcohol. Thin-layer chromatography monitors reactant disappearance at timed intervals; recovered product mass, melting behavior and a UV-visible spectrum provide complementary evidence.
The investigation weighs reaction completion and time against reagent use, proposing a compromise toward the lower part of the tested excess range. Its evaluation is especially useful for distinguishing conversion from isolated yield and for identifying unequal sampling intervals, a single run per condition, balance precision and product-identification limitations.
Why this example is worth reading
A specific chemical tradeoff links the research question, independent variable and evaluation: how much reducing reagent is needed for useful conversion?
The student adapts a published method to available equipment and explains why chromatography, product mass and identification tests answer different questions.
The evaluation quantifies substantial mass and timing uncertainty, acknowledges the lack of replication and identifies unresolved differences in recovered yields.
What to examine critically
The abstract says all reactions reached full conversion, but the detailed discussion identifies an exception at 25% excess. Unequal reaction times, sampling intervals and single runs limit a firm ranking of the conditions.
Thin-layer chromatography shows detectable components rather than a quantitative conversion percentage, and limited product tests do not establish purity conclusively. The claimed green chemistry compromise needs these evidential limits kept visible.
Apply it to your own work
Distinguish disappearance of a reactant, conversion percentage, product identity and isolated yield.
Evaluate the fairness of comparison when procedures change during the investigation.
Use unexpected results to identify a focused follow-up investigation rather than conceal them.
Essay & assessment material
Read the original material alongside the breakdown, or download it to keep.
The examiner mark sheet is embedded on PDF page 3 and records 36/36 under the legacy criteria. No separate narrative examiner commentary is included with this selection; the teaching analysis is our own.
Source & assessment context
IB Chemistry English exemplars, May 2013. The source PDFs retain their original attribution. The analysis on this page is AsterDraft’s independent teaching commentary.
Examiner mark: 36/36 (legacy criteria). The examiner mark sheet is embedded on PDF page 3 and records 36/36 under the legacy criteria. No separate narrative examiner commentary is included with this selection; the teaching analysis is our own.