Using Titration to Analyze

- Using Titration to analyze the unknown [Cl ] in a sample of seawater Relevant Theory: Titration is an analytical method used to determine the unknown amount of a substance by reacting it with a measured amount of another substance called a standardized solution. We will do a lot of titration experiments in Units 4: Acids and Bases. Seawater contains a significant amount of salts, largely sodium chloride. In this activity, a 25.00 ml sample of seawater (in the Erlenmeyer flask) is diluted to 250.0 ml. Then a 25.0 mL sample of this diluted solution is titrated against a standardized solution of 0.100 M silver nitrate (in the Burette). No indicator is necessary. How do you think we can tell when the titration has reached its endpoint? (The point at which you stop the titration). ____________________________________________________________ DATA: Initial Burette Reading (ml) Final Burette Reading (ml) Volume AgNO3 added Trial 1 0.00 14.70 Trial 2 14.70 28.60 Trial 3 28.60 42.35 Average Volume AgNO3 added: _______________ 1. Write a balanced net ionic equation. 2. Calculate the moles of silver nitrate reacted in the titration (using AVERAGE VOLUME). 3. Using the mole ratio from the balanced net ionic equation, calculate the moles of chloride ion present in the seawater sample. - 4. Calculate the [Cl ] in the titration sample. 5. Calculate the concentration of chloride ion in the ORIGINAL sample of seawater. 6. The level of salt in seawater varies across the planet. The average amount of chloride ion in seawater is 21.2 g / L. How does this sample in the experiment compare? 7. Silver ions will form a precipitate with both chloride and chromate ions. Calculate the concentration of Ag+ in a saturated solution of each. Use this information to explain which compound will precipitate first, if a solution containing silver ions is added to a beaker containing both chloride and chromate ions.