Calculating carbohydrates hydrometer lab guide

The eight questions split cleanly into two kinds and it is worth sorting them before you start. Questions one, two, three and eight depend on data you generated — Graph 1, your hydrometer readings, and Data Table 2 — so they cannot be answered from a textbook and they have to be worked from your own sheet. Questions four, five, six and seven are conceptual and can be researched. Doing the data questions first is the better order, because the concepts then have something concrete to explain, and because if your graph turns out to be unusable you want to discover that early rather than after writing four polished paragraphs. Answer the data questions with numbers, units, and the reasoning that got you there, since how do you know this in question one is asking for the method rather than the value. Marks in a post-lab are usually allocated to the reasoning, so a bare number loses most of them.

The calibration logic is the thing the lab is really teaching, so make it explicit at least once. A hydrometer floats at the depth where the mass of fluid it displaces equals its own mass, so a denser liquid supports it higher. Sugar dissolved in water raises density roughly in proportion to concentration, which means a series of known sugar solutions produces a straight-ish line of density against percent sugar, and Graph 1 is that line. Reading an unknown beverage backwards through the line converts a flotation depth into a carbohydrate percentage. Question one asks you to predict where the hydrometer would sit for a 13.0 percent solution, so interpolate from the line and say that you interpolated — that sentence is the answer to how do you know. If 13.0 percent falls between two of your measured standards, say which two you read between; if it falls outside them, say that you extrapolated and note that extrapolation is less reliable.

Percent error in question three is a formula with a convention, so state it: the absolute difference between your measured value and the label value, divided by the label value, times one hundred, with the label treated as the accepted value. Show the substitution for each beverage rather than the result alone. Then discuss the discrepancy honestly, because the lab expects it — labels round, serving sizes differ from what you measured, non-sugar dissolved solids raise density too, and temperature shifts density enough to matter if the samples were not equilibrated. For the conceptual questions, give monosaccharides a chemical answer with the general formula, not just an example; note that carbohydrates supply four Calories per gram; and for alternative methods name real ones such as refractometry, polarimetry, chromatographic sugar analysis, or the by-difference calculation used on nutrition labels, where carbohydrate is what remains after water, protein, fat and ash are measured.