 We have a two-component mixture of sodium hydrogen carbonate and sodium carbonate. We've masked out about 2.5 grams of the mixture. We're going to take that mixture and we're going to add it to an evaporating dish with a watch glass. We've masked the evaporating dish and watch glass previously. We add the solid to the evaporating dish. We cover it. We're now going to slowly add hydrochloric acid to the mixture. The hydrochloric acid will react with the sodium hydrogen carbonate and the sodium carbonate to produce water, sodium chloride, and carbon dioxide gas. The carbon dioxide gas will escape from the reaction mixture. The watch glass prevents any loss of compound from splattering. We'll continue to add the hydrochloric acid until all the compound has reacted. We'll know this by the fact that we will no longer see carbon dioxide being emitted. We'll gently swirl the mixture to make sure that all the compound has a chance to react. After it appears that all the compound has reacted, we'll rinse the bottom of the watch glass to make sure that any compound that may have splattered up on the bottom of the watch glass has a chance to react. We'll then evaporate the mixture to dryness. We've heated the sample to evaporate all the water and the excess HCl. What we're left with is the sodium chloride. We masked the evaporating dish and watch glass, and this allows us to calculate the mass of the sodium chloride produced. We use the mass of sodium chloride to back calculate how much sodium hydrogen carbonate and how much sodium carbonate were in the original sample. We're going to analyze the same two-component system of sodium hydrogen carbonate and sodium carbonate by a volumetric analysis. We've masked out about one gram of the mixture of sodium hydrogen carbonate and sodium carbonate. We're going to add that to 125 milliliter Erlenmeyer flask. We're now going to pipette 25 milliliters of a standardized solution of one molar hydrochloric acid to the mixture. The hydrochloric acid reacts with the sodium hydrogen carbonate and sodium carbonate to produce water, carbon dioxide, and sodium chloride. The carbon dioxide escapes from the reaction mixture. There will be an excess of hydrochloric acid at the end of the reaction. We'll gently swirl the reaction mixture to make sure that the sample gets a chance to react. We know the reaction is complete because we no longer see carbon dioxide being emitted. We'll now rinse the sides of the flask to make sure that all the sample has had a chance to react. We'll add a few drops of phenothaline indicator. Phenothaline is an acid-based indicator. It is colorless and acidic solution and pink and basic solution. We're going to titrate the excess HCl. The phenothaline has already been added to the reaction mixture. We filled the burette with a standardized solution of sodium hydroxide. We've taken an initial burette reading. We're now going to slowly add the sodium hydroxide solution until we reach a pale pink endpoint. We're close to the endpoint. We're going to rinse down the walls of the flask to make sure that anything that is splattered on the walls of the flask has a chance to react. When we reach the pink endpoint, we know that we've added the same number of moles of sodium hydroxide as there was excess HCl. The solution is now turned pale pink. We'll take a final burette reading.