Question

Part I Color changes of Methyl Violet. We will study the following reaction: HMV (aq) + MV (aq) + H* (aq) yellow greenish-blue violet Step 1. Place about 4 mL of distilled water in a regular test tube. Add two drops of methyl violet indicator. Record the color of the solution. Violet Next, add drop by drop, add 6M HCI. This forces equilibrium to be shifted to the left or right-circle the right answer). Adding HCl changes color from to increasingly Step 2. Next, add drop-by-drop 6M NaOH until the color changes from to increasingly Describe in your own words or by writing chemical reaction what happened as you added NaOH. In this step, addition of hydroxide ions shifted the equilibrium from "left to right" or "right to left" - (

Answer 1

HMV (aq) + MV (aq) + H+ (aq) (HMV = protonated methyl violet) Yellow Violet Upon addition of 6M HCl the equilibrium shifts from right to left, and the color gradually changes from violet to yellow Reason: As Htions are added to the solution, the equilibrium will shift towards left hand side according to Le Chatelier's principle as MV will be protonated [MV] * [H] (HMV] Upon addition of 6M NaOH the equilibrium shifts from left to right, and the color gradually changes from yellow to violet Reason: As OH ions are added to the solution, the equilibrium will shift towards right hand side according to Le Chatelier's principle as base will deprotonate HMV Ko=