4 Using Molarity to Calculate Grams of Solute SAMPLE EXERCISE How many grams of Na2SO4 are required to make L of M Na2SO4?Plan: Use the definition of molarity to determine the number of moles of solute, and then convert moles to grams using the molar mass of the solute.Solve: Determine moles of soluteUsing Molar Mass to determine grams
5 Calculating Molar Concentrations of Ions SAMPLE EXERCISE What are the molar concentrations of each of the ions present in a M aqueous solution of calcium nitrate?Plan: Use the subscripts in the chemical formula of the compound to determine the relative concentrations of the ions.Solve: The chemical formula for calcium nitrate is Ca(NO3)2. Because there are two NO3– ions for each Ca2+ ion in the compound, each mole of Ca(NO3)2 that dissolves dissociates into 1 mol of Ca2+ and 2 mol of NO3–. Thus, a solution that is M in Ca(NO3)2 is M in Ca2+ and 2 M = M in NO3–.
6 Acid – Base TitrationThe analytical technique in which one can calculate the concentration of a solute in a solution.
9 Volumetric analysisTitration –deliver a measured volume of a known concentration of titrant into a solution containing the analyte.Titrant – solution of known concentration that is addedAnalyte- solution of unknown concentration that can be analyzedMeasure the volume of titrant added to neutralize the analyte using a color indicator.Titration - Use known volumes of each solution and known concentration of titrant to calculate the concentration of the analyte.
10 Acid Base TitrationsEquivalence point – stoichiometric equivalent quantities of acid and baseIndicator – chemical that changes color at the end pointAcid-base indicators change color at end point.Indicator is chosen so end point corresponds to equivalence point of titration.
11 Using Mass Relations in a Neutralization Reaction SAMPLE EXERCISE How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of M HNO3?Solution
12 Determining the Quantity of Solute by Titration SAMPLE EXERCISE The quantity of Cl– in a municipal water supply is determined by titrating the sample with Ag+. The reaction taking place during the titration is below. The end point in this type of titration is marked by a change in color of a special type of indicator. (a) How many grams of chloride ion are in a sample of the water if 20.2 mL of M Ag+ is needed to react with all the chloride in the sample? (b) If the sample has a mass of 10.0 g, what percent Cl– does it contain?Solution. (a) Plan: We begin by using the volume and molarity of Ag+ to calculate the number of moles of Ag+ used in the titration. We can then use the balanced equation to determine the moles of Cl– in the sample and from that the grams of Cl–.
13 Solution(b) Solve: Comment: Chloride ion is one of the most common ions in water and sewage. Ocean water contains 1.92% Cl–. Whether water containing Cl– tastes salty depends on the other ions present. If the only accompanying ions are Na+, a salty taste may be detected with as little as 0.03% Cl–.
14 ConclusionUse Molarity to calculate molarity and then use stoichiometry to determine moles or grams in a chemical reaction.Use titration to neutralize solution of unknown concentration with color indicator. The titrant has known concentration and measured volume. Using stoichiometry, the unknown concentration can be determined.