Lab 3 Colorimetric Testing

Reducing sugar

A sugar capable of acting as a reducing agent due to a free aldehyde or ketone group; glucose is an example. Benedict’s reagent detects reducing sugars and changes blue to orange/red with Cu2O precipitate.

Benedict’s reagent

A colorimetric reagent that detects reducing sugars; blue when negative, turns orange‑red with reducing sugars due to reduction of Cu(II) to Cu2O.

Starch

Polysaccharide polymer of glucose; detected by iodine (IKI); presence yields blue‑black color and helps distinguish starch from monosaccharides and disaccharides.

IKI (Iodine) test

Indicator dye used to test for starch; positive test yields blue‑black color; negative test yields yellowish‑brown.

Monosaccharides

Simple sugars; typically end in -ose; can be absorbed directly without further digestion.

Disaccharides

Sugars composed of two monosaccharides; must be broken down by digestive enzymes before absorption.

Protein testing

Biuret reagent detects peptide bonds in proteins; copper(II) binds to nitrogens in peptides; positive test yields purple; negative test remains blue.

Biuret reagent

Reagent used to test for proteins; forms a purple complex with peptide bonds when proteins are present.

Qualitative data

Data indicating presence/absence or approximate values, often obtained from colorimetric indicators.

Quantitative data

Data providing precise measurements and numerical values.

Indicator dyes

Reagents that change color in different environments, providing a quick qualitative indication of presence or absence.

Positive control

A sample known to contain the target substance to confirm the test works (ex. starch solution as a positive control).

Negative control

A sample known not to contain the target substance to establish a baseline (ex. deionized water).

Anabolism

Synthesis reactions building polymers from monomers; energy is typically required.

Catabolism

Hydrolysis reactions breaking polymers into monomers; energy is typically released.

Metabolism

Sum of all chemical reactions ongoing in the body.

Starch test result

Positive: blue‑black color with IKI; Negative: yellowish brown.

Protein test result

Positive: purple color with Biuret reagent; Negative: light blue.