Part I: SOLUTION STOICHIOMETRY Chapter Four: Part I: SOLUTION STOICHIOMETRY AP Chemistry Ms. Paskowski

Water, the Common Solvent One of the most important substances on earth Can dissolve many different substances A polar molecule 4.1

Dissolution of a Solid in a Liquid 4.1

Nature of Aqueous Solutions Solute – substance being dissolved Solvent – liquid water Electrolyte – substance that when dissolved in water produces a solution that can conduct electricity 4.2

Electrolytes Strong Electrolytes – conduct current very efficiently (bulb shines brightly) Weak Electrolytes – conduct only a small current (bulb glows dimly) Nonelectrolytes – no current flows (bulb remains unlit) 4.2

Electrolyte Behavior 4.2

Chemical Reactions of Solutions We must know: Nature of the reaction Amounts of chemicals present in the solutions 4.3

Molarity Molarity (M) = moles of solute per volume of solution in liters: 4.3

Concept Check Which of the following solutions contains the greatest number of ions? 400.0 mL of 0.10 M NaCl. 300.0 mL of 0.10 M CaCl2. 200.0 mL of 0.10 M FeCl3. 800.0 mL of 0.10 M sucrose. a) contains 0.080 mol of ions (0.400×0.10×2). b) contains 0.090 mol of ions (0.300×0.10×3). c) contains 0.080 mol of ions (0.200×0.10×4). d) does not contain any ions because sucrose does not break up into ions. Therefore, letter b) is correct. 4.3

Let’s Think About It Draw molecular level pictures showing each solution. Think about relative numbers of ions. How many moles of each ion are in each solution? 4.3

Notice The solution with the greatest number of ions is not necessarily the one in which: the volume of the solution is the largest. the formula unit has the greatest number of ions. 4.3

Dilution The process of adding water to a stock solution to achieve the molarity desired for a particular solution. Dilution with water does not alter the numbers of moles of solute present. Moles of solute before dilution = moles of solute after dilution M1V1 = M2V2 4.3