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

(a) Butterfat in homogenized milk is hydrophobic, (b) hemoglobin in blood is hydrophilic, (c) vegetable oil in a salad dressing is hydrophobic, and (d) colloidal gold particles in water are hydrophilic.

Step-by-step solution

(a) Butterfat in homogenized milk

Butterfat is a lipid that repels water, making it hydrophobic. However, when it is dispersed in homogenized milk, the milk proteins help to form stable emulsions (tiny droplets). The interaction with milk proteins makes butterfat hydrophobic, while the surrounding proteins in the milk allow it to mix better with water.

(b) Hemoglobin in blood

Hemoglobin is a protein found in red blood cells, responsible for oxygen transport. Proteins are generally made up of a combination of hydrophilic and hydrophobic amino acids. However, in the case of hemoglobin, it is soluble in water and functions in a watery environment, which makes it hydrophilic.

(c) Vegetable oil in a salad dressing

Vegetable oil is primarily composed of lipids. Lipids are hydrophobic molecules that repel water. In a salad dressing, an emulsifying agent (such as vinegar or mustard) is often added to help the oil mix with water-based ingredients, but the oil itself remains hydrophobic.

(d) Colloidal gold particles in water

Colloidal gold particles are composed of tiny metallic gold nanoparticles suspended in a dispersing medium, such as water. Due to their charged surface and interaction with the water molecules, colloidal gold particles exhibit hydrophilic behavior, allowing them to be well-dispersed in water.