A fresh cup of black coffee is a homogeneous liquid
CHEMISTRY · Single correct · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A fresh cup of black coffee is a homogeneous liquid. After cream is added and the mixture is briefly stirred, the cup is left undisturbed for several hours, during which a lighter layer forms near the top and a darker layer remains below. Which of the following classifications of the coffee–cream mixture is most accurate before stirring and after the layers appear?
(a) Homogeneous both before stirring and after layers form, because the coffee and cream are completely miscible.
(b) Homogeneous before stirring and heterogeneous after layers form, because the mixture starts out uniform but later separates under gravity.
(c) Heterogeneous both before stirring and after layers form, because two distinct layers are present at each of those times.
(d) Heterogeneous before stirring and homogeneous after layers form, because the cream ultimately spreads out in a single phase at the top.