To calculate the pH of a 0.2 M solution of acetic acid, we will use the formula for the acid dissociation constant Ka and the definition of pH.The dissociation of acetic acid CHCOOH in water can be represented as follows:CHCOOH CHCOO + HThe Ka expression for this reaction is:Ka = [CHCOO][H] / [CHCOOH]We can assume that the initial concentration of CHCOO and H is 0, and the initial concentration of CHCOOH is 0.2 M. Let x be the concentration of H ions at equilibrium. Then, the concentration of CHCOO ions will also be x, and the concentration of CHCOOH will be 0.2 - x.Now, we can substitute these values into the Ka expression:1.8 10 = x x / 0.2 - x Since Ka is very small, we can assume that x is much smaller than 0.2, so 0.2 - x 0.2:1.8 10 x / 0.2Now, we can solve for x:x = 1.8 10 * 0.2x = 3.6 10x = 3.6 10 x 1.9 10Now that we have the concentration of H ions x , we can calculate the pH using the pH formula:pH = -log[H]pH = -log 1.9 10 pH 2.72The pH of the 0.2 M solution of acetic acid is approximately 2.72.