1. Stoichiometry: Quantitative Information About Chemical Reactions Chapter 4

2. Overview Mass Relationships in Chemical Reactions: Stoichiometry Reactions in Which One Reactant Is Present in Limited Supply Percent Yield Chemical Equations and Chemical Analysis

3. Overview Measuring Concentrations of Compounds in Solution pH, a Concentration Scale for Acids and Bases Stoichiometry of Reactions in Aqueous Solution Spectrophotometry, Another Method of Analysis

4. Chapter Goals Perform stoichiometry calculations using balanced chemical equations. Understand the theoretical and percent yields of a chemical reaction. Use stoichiometry to analyze a mixture of compounds or to determine the formula of a compound. Define and use concentration in solution stoichiometry.

5. Molarity Molarity is a quantitative way to measure the concentration of a solution by looking at the amount of solute (in Mole) per liter of total solution. Concentration (c or M) = mole solute / L sol’n

6. Molarity If 25.3g of sodium carbonate is dissolved in enough water to make 250. mL of solution, what is the molar concentration of Na 2 CO 3 ? [Na 2 CO 3 ] = 0.955M If 26.3g of sodium bicarbonate is dissolved in enough water to make a 200. mL solution, what is the concentration of the solution?

7. Preparing Solutions of Known Concentrations Suppose you want to prepare 2.00L of a 1.50M solution of sodium carbonate. You have some solid sodium carbonate and some distilled water. You also have a 2.00L volumetric flask. To make the solution you must weigh the necessary amount of sodium carbonate, carefully place it in the volumetric flask and add water to dissolve the solid.

8. Preparing Solutions of Known Concentrations After the solid is completely dissolved more water is added to bring the solution volume to 2.00L. The solution then has the desired concentration and the volume specified. But what mass of sodium carbonate is required? Start with volume and use factor label to get into grams of solute. L  moles  grams

9. Check and See An experiment in your laboratory requires 250. mL of a 0.0200M solution of silver nitrate. You are given solid silver nitrate, distilled water and a 250. mL volumetric flask. Describe how to make the solution.

10. Diluting a More Concentrated Solution If you have a solution already prepared and it is too concentrated for you experiment, then you must use the method of dilution to get the desired concentration. M 1 V 1 = M 2 V 2 or c 1 V 1 = c 2 V 2 An experiment calls for you to use 250. mL of 1.00M NaOH, but you are given a large bottle of 2.00M NaOH. Describe how to make the 1.00M NaOH in the desired volume.

11. pH: A Conc. Scale for Acids & Bases Acids produce H + in solution. The pH of a solution is the negative of the log of hydrogen ion concentration. pH = -log [H + ] If you know the pH and you want to know [H + ], [H + ] = 10 -pH Lemon juice has [H + ] = 0.0032M. What is its pH? Sea water has a pH = 8.30. What is the hydrogen ion concentration of this solution?

12. Stoichiometry of Reactions is Aqueous Solution Write the balanced equation for solid calcium carbonate reacting with aqueous hydrochloric acid. Suppose we want to know what mass of calcium carbonate is required to react completely with 25mL of 0.750M HCl. This is the same as all stoichiometry problems except you must find the amount of moles of HCl using the volume and concentration of HCl.

13. Check and See Metallic zinc reacts with aqueous HCl according to what equation? What volume of 2.50M HCl is required to convert 11.8g of Zn completely to products? 0.100L HCl

14. Titrations A substance, present in unknown quantities, can be allowed to react with a known quantity of another substance. If the stoichiometric ratio for their reaction is known, the unknown quantity can be determined. Oxalic acid, H 2 C 2 O 4, is a naturally occurring acid. Suppose you are asked to analyze a sample of oxalic acid to determine its purity.

15. Titrations Because it is an acid, we know how it reacts with sodium hydroxide to produce a salt and water. Write the equation…

16. Titrations If you know the amount of a certain concentration base needed to react all of the acid, you could determine the purity of the acid. A process called titration is used. The acid is placed in a flask with an acid- base indicator—that changes colors in acidic/neutral/basic solutions.

17. Titrations A known concentration of NaOH is placed in a burette tube and small amount of base are added to the acid/indicator solution until the reaction shows just neutral. Calculations can then be done to determine the concentration of the acid.

18. Check and See A 1.034g sample of impure oxalic acid is dissolved in water and an acid-base indicator added. The sample requires 34.47mL of 0.485M NaOH to reach the equivalence. What is the mass of oxalic acid and what is its mass percent in the sample?