Solutions Dr. Ron Rusay Fall 2001

Aqueous Reactions & Solutions  Many reactions are done in a homogeneous liquid or gas phase which generally improves reaction rates.  The prime medium for many inorganic reactions is water which serves as a solvent (the substance present in the larger amount), but does not react itself.  The substance(s) dissolved in the solvent is (are) the solute(s). Together they comprise a solution. The reactants are the solutes. © Copyright R.J. Rusay

Water : “The Universal” Solvent Generally, likes dissolve likes, i.e. polar-polar and nonpolar-nonpolar. If polar and nonpolar mix, eg. oil and water: The oil (nonpolar) and water (polar) mixture don’t mix and are immiscible. If liquids form a homogeneous mixture, they are miscible.

Salt dissolving in a glass of water

Water dissolving an ionic solid

Concentration and Temperature Besides amount, the rate also increases. What are two other ways of increasing the solubility of a solid, eg. sugar in coffee? Relative Solution Concentrations: Saturated Unsaturated Supersaturated

Gas Solubility P 2 = P 1 x [P 2 / P 1 ] P is the partial pressure of the gas vapor. Solubility units (Concentration) are usually: g / 100 ml

Preparation of Solutions

Solution Concentration  A solution’s concentration is the measure of the amount of solute dissolved.  Concentration is expressed in several ways. One way is mass percent. Mass % = Mass solute / [Mass solute + Mass solvent ] x100  What is the mass % of 65.0 g of glucose dissolved in 135 g of water? Mass % = 65.0 g / [ ]g x100 = 32.5 % = 32.5 % © Copyright R.J. Rusay

Solution Concentration  Concentration is expressed more importantly as molarity (M). Molarity (M) = Moles solute / Liter Solution  An important relationship is M x V solution = mol  This relationship can be used directly in mass calculations of chemical reactions.  What is the molarity of a solution of 1.00 g KCl in 75.0 mL of solution? M = 1.00g KCl x 1mol KCl / g KCl x 1/ 75mL x 1000mL / L = 0.18 mol / L © Copyright R.J. Rusay

Solution Dilution

Solution Dilution Calculations  The following formula can be used in dilution calculations: M 1 V 1 = M 2 V 2 M 1 V 1 = M 2 V 2  A concentrated stock solution is much easier to prepare and then dilute rather than preparing a dilute solution directly. Concentrated sulfuric acid is 18M. What volume would be needed to prepare 250mL of a 1.5M solution?  V 1 = M 2 V 2 / M 1  V 1 = 1.5 M x 250 mL / 18 M = 20.8 mL © Copyright R.J. Rusay

1) What is the mass of copper(II)chloride in 25.0 mL of a 0.500M solution? mass CuCl2 = ? © Copyright R.J. Rusay Solution Problems 2) mL of concentrated acetic acid (17M) was diluted to make exactly mL of solution. What is M 2 = ? 3) 50.0 mL of a 0.100M MgBr 2 solution reacted completely with 13.9 mL of a silver nitrate solution. M AgNO3 = ? ; mass AgBr = ? 1.81g 0.34 M M 1.88 g