One 6 well plate, small stir rod, small rinse beaker.
50-60 mL of DI water, Alka-Seltzer tablet, universal indicator and solutions of 1 M HCl and 1 M NaOH.
- Add 20-25 drops of universal indicator to the DI water.
- Pour equal amounts of the DI water w/ indicator into each of the six wells, approximately 10 mL.
- Break the Alka-Seltzer tablet and choose two pieces of approximately equal mass in the 0.15-0.20 g range.
- Add one Alka-Seltzer piece to well 3 and the other to well 6 and stir.
- Add one drop of 1 M HCl to well 1 and one drop of 1 M NaOH to well 4 and stir.
- Add HCl to well 3 in 5 drop intervals with stirring until the color in well 3 matches the color in well 1. This will take approximately 25 drops.
- Add NaOH to well 6 in 5 drop intervals with stirring until the color in well 6 matches the color in well 3. This will take approximately 25 drops.
Hydrochloric acid can irritate the skin. Hydrochloric acid vapors are extremely irritating to the eyes and respiratory system. Therefore, it should be handled only in well-ventilated area. Solid sodium hydroxide and concentrated solutions can cause severe burns to eyes, skin, and mucous membranes.
An Alka-Seltzer tablet contains 1.9 g (0.022 mole) of sodium bicarbonate and 1.0 g (0.005 mole) of citric acid. Keep in mind we are using fractions of this. When the tablet is added to water, the citric acid reacts with the bicarbonate, producing citrate and carbon dioxide gas.The balanced reaction and the starting amounts of sodium bicarbonate show that there is an excess of the bicarbonate ion. This excess is responsible for the buffering effect of the Alka-Seltzer. The bicarbonate can react with excess acid, 3HCO3-(aq) + H3C3H5O7 (aq) ® C3H5O73-(aq) + 3CO2 (g) + 3H2O (l)Or the bicarbonate can react with excess base. HCO3-(aq) + H+(aq) ® CO2 (g) + H2O (l)