Read Section 5.5 before viewing the slide show.

Unit 20 Solution Terminology (5.5) Definition of Solution Terms Associated with Solutions Concentrations of Solutions – Molarity and % by Mass

Definition and Types of Solutions A solution is a homogeneous mixture of two or more components. Solutions are typically recognized to have two parts: Solvent – the component present in the largest quantity Solute – all of the components that are not the solvent Solutions can be made from combinations of any of the three states of matter: State of Solvent State of Solute Example gas air liquidgasdissolved gases in water, such as oxygen liquid alcohol in water liquidsolidsugar in water solidgashydrogen in a metal solidliquidmercury in silver solid silver in gold

Terms Associated with Solutions The quantity of solute in a solution may vary over a wide range. Terms have come into use to describe qualitatively the levels of solute dissolved. Dilute solution – does not contain very much solute per quantity of solution Concentrated solution – has a large amount of solute per quantity of solution Saturated solution – contains all of the solute the given amount of solvent can hold at the temperature and pressure being considered Unsaturated solution – contains less solute than the solvent could hold at the temperature and pressure being considered Supersaturated solution – solvent contains more solvent than it can at the saturated level. These solutions are unstable and the solute will come out of solution if disturbed. Pictorially

Quantitative Solution Expressions As useful as it is to have qualitative descriptors of solution concentrations, numeric descriptors are much more helpful in describing chemical processes. Three primary expressions we will consider: Each has the form of mass or mol of solute divided by mass or volume of solution Each can serve as a conversion factor for conducting calculations

Molarity Consider molarity first: Examples: Suppose 15.0-g of NaCl is dissolved in 250 mL of solution. Find the molarity. First need to find the number of moles of solute, NaCl. That is given by: The molarity then is given by: How many mol of NH 3 are contained in 75.0 mL of M NH 3 ? Try the conversion factor approach where M NH 3 can be thought of as mol NH 3 per 1 L solution.

% by Volume Next consider % by volume: Examples: Suppose 15.0-mL of ethyl alcohol is dissolved in 250 mL of solution. Find the % by volume. This becomes a simple substitution: How many mL of ethyl alcohol are contained in 75.0 mL of 15.5% by volume ethyl alcohol? Try the conversion factor approach where 15.5% by volume of ethyl alcohol can be thought of as 15.5 mL of ethyl alcohol per 100 mL solution – that is what a percent amounts to.

% by Mass And finally consider % by volume: Examples: Suppose 15.0-g of NaCl is dissolved in 250 g of water. Find the % by mass. Notice the denominator is the mass of solution – it has both the solute and solvent masses included so the two masses must be added together for a total solution mass of 15.0 g g = 265 g of solution. How many g of NH 3 are contained in 75.0 g of a solution that is 15.5% by mass NH 3 ? Try the conversion factor approach where 15.5% by mass NH 3 can be thought of as 15.5 g NH 3 per 100 g solution – that is what a percent amounts to.