9/11/2013 1 S O L U T I O N S Solute Solvent “Like Dissolves Like

9/11/2013 Solute S A solute is the dissolved substance in a o solution. l Salt in salt water Sugar in soda drinks u Carbon dioxide in soda drinks t Solvent i A solvent is the dissolving medium in a o solution. n Water in salt water Water in soda s “Like Dissolves Like” Solubility Trends Nonpolar solutes dissolve best in nonpolar The solubility of MOST solids increases solvents with temperature. Fats Benzene The rate at which solids dissolve increases Steroids Hexane with increasing surface area of the solid. Waxes Toluene The solubility of gases decreases with increases in temperature. Polar and ionic solutes dissolve best in polar The solubility of gases increases with the solvents pressure above the solution. Inorganic Salts Water Sugars Small alcohols Acetic acid 1 9/11/2013 Solubility Chart Therefore… Solids tend to dissolve best when: o Heated o Stirred o Ground into small particles Gases tend to dissolve best when: o The solution is cold o Pressure is high Definition of Electrolytes and Saturation of Solutions Nonelectrolytes A solution that contains the maximum amount of solute that may be dissolved under existing An electrolyte is: conditions is saturated. A solution that contains less solute than a A substance whose aqueous solution saturated solution under existing conditions is conducts an electric current. unsaturated. A solution that contains more dissolved solute A nonelectrolyte is: than a saturated solution under the same conditions is supersaturated. A substance whose aqueous solution does not conduct an electric current. 2 9/11/2013 Electrolytes vs. Nonelectrolytes Try to classify the following substances as electrolytes or nonelectrolytes… 1.1.PurePure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution The ammeter measures the flow of electrons (current) 5.Hydrochloric acid solution through the circuit. 6.Lactic acid solution If the ammeter measures a current, and the bulb 7.Ethyl alcohol solution glows, then the solution conducts. If the ammeter fails to measure a current, and the 8.Pure sodium chloride bulb does not glow, the solution is non-conducting. Answers to Electrolytes Ionic Compounds “Dissociate” ELECTROLYTES: NONELECTROLYTES: NaCl(s) Na +(aq) + Cl -(aq) Tap water (weak) Pure water + - NaCl solution Sugar solution AgNO 3(s) Ag (aq) + NO 3 (aq) HCl solution Ethanol solution 2+ - MgCl 2(s) Mg (aq) + 2 Cl (aq) Lactate solution (weak) Pure NaCl + 2- Na 2SO 4(s) 2 Na (aq) + SO 4 (aq) 3+ - AlCl 3(s) Al (aq) + 3 Cl (aq) 3 9/11/2013 Ions tend to stay in solution where they can Some covalent compounds IONIZE in solution conduct a current rather than re-forming a solid. Covalent acids form ions in solution, with the The reason for this is help of the water molecules. the polar nature of the water molecule… For instance, hydrogen chloride molecules, Positive ions associate with the negative which are polar, give up their hydrogens to end of the water dipole (oxygen). water, forming chloride ions (Cl -) and Negative ions associate with the positive hydronium ions (H O+). end of the water dipole (hydrogen). 3 Strong acids such as HCl are completely Weak acids such as lactic ionized in solution. acid usually ionize less than 5% of the time. Other examples of strong acids include: Sulfuric acid, H 2SO 4 Nitric acid, HNO 3 Many of these weaker acids Hydriodic acid, HI are “organic” acids that contain Perchloric acid, HClO 4 a “carboxyl” group. The carboxyl group does not easily give up its hydrogen. 4 9/11/2013 Because of the carboxyl group, organic acids are sometimes called “carboxylic acids”. Other organic acids and their sources include: o Citric acid – citrus fruit o Malic acid – apples o Butyric acid – rancid butter o Amino acids – protein o Nucleic acids – DNA and RNA o Ascorbic acid – Vitamin C This is an enormous group of compounds; these are only a few examples. 5.

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