Question

Indicate whether each of the following is a hydrophilic or a hydrophobic colloid: (a) butterfat in homogenized milk, (b) hemoglobin in blood, (c) vegetable oil in a salad dressing, (d) colloidal gold particles in water.

Short answer

The given colloids can be classified as hydrophilic or hydrophobic as follows: (a) Butterfat in homogenized milk is a hydrophobic colloid, (b) Hemoglobin in blood is a hydrophilic colloid, (c) Vegetable oil in a salad dressing is a hydrophobic colloid, and (d) Colloidal gold particles in water are a hydrophilic colloid.

Step-by-step solution

(a) Butterfat in homogenized milk

Butterfat is primarily composed of lipids, which are hydrophobic molecules that do not mix well with water. However, milk is an emulsion, meaning that the hydrophobic butterfat is mixed in a stable form with the aqueous components of milk. So, butterfat in homogenized milk is a hydrophobic colloid.

(b) Hemoglobin in blood

Hemoglobin is a protein found in red blood cells that is responsible for the transport of oxygen and carbon dioxide in the body. Proteins, as a general rule, have hydrophilic and hydrophobic regions which help them dissolve in different environments. Since hemoglobin functions in the aqueous environment of blood, its overall interaction with water is hydrophilic. Thus, hemoglobin in blood is a hydrophilic colloid.

(c) Vegetable oil in a salad dressing

Vegetable oils are composed mainly of lipids, specifically triglycerides, which are hydrophobic molecules that do not mix well with water. When mixed with water or any aqueous solution, vegetable oil forms droplets and does not dissolve. Therefore, vegetable oil in a salad dressing is a hydrophobic colloid.

(d) Colloidal gold particles in water

Colloidal gold is a suspension of gold nanoparticles in water or another liquid. These gold particles are usually coated with a layer of some hydrophilic substance, such as a negatively charged surface layer, enabling the gold particles to disperse uniformly in the aqueous medium. Consequently, colloidal gold particles in water are considered a hydrophilic colloid.