This color change indicates a pH change caused by the diffusion of CO 2 gas into the liquid. Thus, after a short time, the surface of the indicator solution changes color: from blue to yellow if you’re using bromothymol blue or from purple to pale pink if you’re using cabbage-juice indicator. Even so, the presence of this acid affects the pH of the solution. When CO 2 gas diffuses into water, the following chemical reaction takes place and results in carbonic acid ( H 2 CO 3 ):Ĭarbonic acid dissociates into H + and HCO 3 -. The increase in H + causes the solution to become more acidic.Ĭarbonic acid is a weak acid. The CO 2 gas then diffuses into the liquid below. Mixing vinegar and baking soda together in the paper cup creates carbon dioxide gas ( CO 2 ). It also models part of the short-term carbon cycle-specifically the interaction between our atmosphere and the ocean’s surface. This activity illustrates how the diffusion of a gas into a liquid can cause ocean acidification. Immediately place a Petri dish over the top of each plastic cup.
Be very careful not to spill any vinegar into the indicator solution. Place both clear plastic cups onto a sheet of white paper and arrange another piece of white paper behind the cups as a backdrop (this makes it easier to see the change).Ĭarefully add 1 teaspoon (about 5-6 mL) of white vinegar to the paper cup containing the baking soda (image below). The second plastic cup containing indicator solution will be your control. Make sure the bottom of the paper cup is not touching the surface of the liquid in the plastic cup-you don’t want the paper cut to get wet. Tape the paper cup inside one of the clear plastic cups containing the indicator solution so that the top of the paper cup is about 1/2 inch (roughly 1 centimeter) below the top of the plastic cup. Pour 1 1/2 fluid ounces (40–50 mL) of acid-base indicator solution into each of the two clear plastic cups.Īdd 1/2 teaspoon (2 grams) of baking soda to the paper cup.
0 kommentar(er)
