Water and Solutions Concentration

2 9.1 Solutes, Solvents, and Water concentration: the amount of each solute compared to the total solution. Concentration

3 9.1 Solutes, Solvents, and Water Concentration More soluteLess solute How can we express concentration quantitatively (with numbers)?

4 9.1 Solutes, Solvents, and Water Concentration There are several ways to express concentration

5 9.1 Solutes, Solvents, and Water Suppose you dissolve 10.0 g of sugar in 90.0 g of water. What is the mass percent concentration of sugar in the solution?

6 9.1 Solutes, Solvents, and Water Concentration Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water.

7 9.1 Solutes, Solvents, and Water What happens when you add 10 g of sugar to 100 mL of water? sugar 100 mL H 2 O 10 g Conc. (%) = 10 g/110 g Solubility Water molecules dissolve sugar molecules …

8 9.1 Solutes, Solvents, and Water Then when two sugar molecules find each other, they will become “undissolved” (solid) again… … then, they become redissolved in water again. Solubility

9 9.1 Solutes, Solvents, and Water This is an aqueous equilibrium! The solution is “saturated Equilibrium Solubility saturation: situation that occurs when the amount of dissolved solute in a solution gets high enough that the rate of “undissolving” matches the rate of dissolving.

Solutes, Solvents, and Water Temperature has an effect on solubility Temperature and solubility 210 g sugar 100 mL H 2 O 20 o C Undissolved sugar 210 g sugar 100 mL H 2 O 30 o C All the sugar is dissolved

Solutes, Solvents, and Water solubility: the amount of a solute that will dissolve in a particular solvent at a particular temperature and pressure.

Solutes, Solvents, and Water Temperature and solubility You can dissolve (a lot) more sugar at higher temperatures

Solutes, Solvents, and Water Temperature and solubility Sugar becomes “undissolved” (solid) as the temperature goes down

Solutes, Solvents, and Water Temperature and solubility Temperature does not have the same effect on the solubility of all solutes

Solutes, Solvents, and Water Temperature affects: - the solubility of solutes how much - the rate of solubility how fast

Solutes, Solvents, and Water Dissolving is a collision process Slow (cold) molecules are not as effective as fast (hot) molecules Salt dissolves faster in hot water Dissolving rate

Solutes, Solvents, and Water Dissolving rate Substances are often ground up into powder to make them dissolve faster A 1 cm cube has a surface area of 6 cm 2 The same volume has a surface area of 9 cm 2 when divided up into smaller cubes

Solutes, Solvents, and Water The rate of solubility increases: - with an increase in temperature - with an increase in surface area of the solute

Solutes, Solvents, and Water Solubility of common gases in water at 25 o C At higher temperatures: - solid solutes (like salt and sugar) are more soluble - gases are less soluble

Solutes, Solvents, and Water Seltzer water is a supersaturated solution of CO 2 in water supersaturation: term used to describe when a solution contains more dissolved solute than it can hold. This solution is unstable, and the gas “undissolves” rapidly (bubbles escaping) Hand warmer is a supersaturated solution of sodium acetate This solution is unstable, and the particles “undissolve” rapidly turning into a solid and giving off heat