Commercial whole milk is often described as a "colloid" in which fat droplets are…
CHEMISTRY · Multi-part · CBSE · Chemistry · Is Matter Around Us Pure? · Is Matter Around Us Pure?
Problem
Commercial whole milk is often described as a "colloid" in which fat droplets are dispersed in an aqueous phase containing proteins, lactose, and minerals. A food chemist wishes to investigate whether whole milk that has been allowed to stand undisturbed for 24 h at 4 °C is better described as a homogeneous or a heterogeneous mixture.
(a) Design a detailed experimental procedure—using equipment commonly available in an AP-level chemistry laboratory—that would allow the chemist to evaluate the spatial uniformity of the milk's composition after standing. Your design should specify:
• what property or properties will be measured;
• how and where within the sample the measurements will be taken;
• the criteria for deciding whether the mixture is homogeneous or heterogeneous.
(b) Predict the observations or data you would expect if the milk is heterogeneous after 24 h. Explain the chemical basis for each predicted observation, referring to relevant inter-particle forces or physical processes.
(c) Ultra-high-pressure homogenization can reduce the diameter of fat droplets in milk to below 0.2 µm. Explain how this treatment could affect the outcome of the experiment you designed in part (a), and discuss whether the treated milk would be more likely to behave as a homogeneous or heterogeneous mixture on the macroscopic scale.
(d) Evaluate ONE limitation of your experimental design in part (a) and propose a modification or supplementary test that could address this limitation.