Lecture 2--Quantitative Description of Solution Properties

Lecture 2--Quantitative Description of Solution Properties...

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Quantitative Description of Solution Properties Ch 302, Fall 2009 B. A. Rowland August 31, 2009
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An Outline In the last lecture we discussed solutions and the properties of water that make it the ‘universal solvent’. We know that many things can be dissolved in water. We will explore the use of electrical conductivity to characterize solutions. We would like to be able to quantify how much solute is dissolved in a given volume of solvent. This idea is known as a solution’s concentration . Today, we will discuss concentration, and the ways it may be expressed. Of focus will be Mass Percent (also known as weight percent), parts per million (ppm), parts per billion (ppb), Molarity (M), and Molality (m). We will also discuss the way by which you may dilute one solution to give a solution of different strength.
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Characterization of Solutions: Electrical Conductivity The ability of a solution to conduct an electrical current is known as electrical conductivity . The figure to the right demonstrates this. If the solution conducts electricity, the light shines, if not, then no light is produced. There are three ways we can characterize a solution: Strong electrolytes are solutions which very efficiently conduct electricity. The light will shine very brightly in this case. Weak electrolytes are solutions which conducts only a very small amount of electricity. The light will shine very dimly. Nonelectrolytes are solutions which conduct no electricity. In this case the light will not shine at all . The idea that some solutes can dissociate in aqueous solution was proposed by Arrhenius in the 1880s. This was his postulation as to why some solutions conduct a current. Note that pure water will NEVER conduct an electric current.
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Strong Electrolytes Strong electrolytes produce large amounts of ions. Strong electrolytes can be classified as soluble salts, strong acids, and strong bases. YOU NEED TO MEMORIZE THE STRONG ACIDS AND THE STRONG BASES! Strong Acids: perchloric acid (HClO 4 ), hydroiodic acid (HI), hydrobromic acid (HBr), hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 )—first dissociation only, hydronium ion (H 3 O + ), and nitric acid (HNO 3 ). Strong Bases:
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Lecture 2--Quantitative Description of Solution Properties...

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