Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Properties of Aqueous Solutions Precipitation Reactions Acid Base Reactions Concentrations of Solutions Solution Stoichiometry

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four A solution is a homogenous mixture that consists of the solvent: the component in the solution present in the largest amount. In aqueous solutions, water is the solvent. the solutes: the other components in the solution Electrolytes are solutes that, when dissolved in water, cause the solution to conduct electricity Properties of Aqueous Solutions

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four A solution is a homogenous mixture that consists of the solvent: the component in the solution present in the largest amount. In aqueous solutions, water is the solvent. the solutes: the other components in the solution Electrolytes are solutes that, when dissolved in water, cause the solution to conduct electricity Strong electrolyte: a compound that, when dissolved in water, dissociates completely into mobile ions that effect the conduction of electricity. Weak electrolyte: a compound that, when dissolved in water, dissociates only slightly into mobile ions that effect the conduction of electricity.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Water solvates strong electrolytes by surrounding cations with partially negative oxygen directed inward, and surrounding anions with partially positive hydrogens directed inwards.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four When aqueous silver nitrate (AgNO 3 )is added to aqueous sodium chloride (NaCl), a white solid forms. This precipitate is silver chloride (AgCl)

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four The solubility rules provide guidelines for deciding which compounds are soluble and which are insoluble

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four The solubility rules provide guidelines for deciding which compounds are soluble and which are insoluble Generally, you need to know that the following ionic compounds are soluble: Use these rules and/or the Solubility Table to predict the results of a metathesis reaction.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Metathesis Reactions Reactions in which cations and anions appear to exchange partners. When aqueous lead (II) acetate is mixed with aqueous sodium chloride, a metathesis reaction occurs, forming an insoluble precipitate. A more accurate way to depict this reaction is to list the species actually present in aqueous solution, the ions themselves produces the net ionic equation

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Acids are substances that produce hydrogen ions (H + ) when dissolved in water. Because a hydrogen atom consists of one proton and one electron, a hydrogen ion is a proton. Thus, acids are often defined as proton donors There are seven common strong acids (Table 4.2) that must be memorized. Bases are substances that consume hydrogen ions (H + ) when dissolved in water. Bases often produce hydroxide ion when they dissolve in water. The most common strong bases are the metal hydroxides (eg. NaOH, Ca(OH) 2, Al(OH) 3, etc.)

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Strong acids/bases are strong electrolytes that dissociate completely. Weak acids/bases are weak electrolytes that dissociate only slightly.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Acid/Base Reactions Reactions between strong acids and bases are similar to metathesis rxns. One of the products is water. Consider the reaction of sulfuric acid with potassium hydroxide. Again the most accurate way to describe this reaction is by considering the ions themselves produces the net ionic equation

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Concentration of Solutions Suppose 1.0 moles of hydrochloric acid is dissolved in 500 ml of water. 0.1 moles H moles Cl - We define the Molarity (M) of solute A in a solution as

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four 0.1 moles H moles Cl - Suppose 200 mL were removed and placed in a separate flask.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Solution Concentrations The concentration of a solution is independent of the amount (intensive property) and can be used to convert between volume and moles. How many moles of HCl are in 50 mL of a 2.0 M solution? What volume of this solution would provide 0.36 moles of HCl?

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four If 25 mL of a 1.0 M solution of copper II sulfate is transferred to a 250 mL volumetric flask and the solution is diluted to volume with water, what is the concentration of the new solution? Moles of CuSO 4 : Molarity of soln:

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four What volume of 0.56 M sulfuric acid solution must be mixed with sufficient water to create 325 mL of 0.15 M sulfuric acid? Moles of H 2 SO 4 : Volume of soln: What volume of this new sulfuric acid solution is needed to completely react 2.56 g of potassium hydroxide?

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Four Supplement: Measuring Acidity: The pH Scale In aqueous solution, the concentration of hydrogen ions [H + ] typically ranges form 1.0 M to 1x M To provide a convenient way to describe acidity, the pH scale was defined: Because the scale involves a minus sign, acidic solutions, with high hydrogen ion concentrations, have low pH. Thus, the pH of a solution for which [H + ] = M is