solubility solubilities that increase with increasing temperature

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1 Solubility The concentration of the solute in a saturated solution is the solubility of the solute About 95% of all ionic compounds have aqueous solubilities that increase with increasing temperature

2 Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature

3 Temperature and Solubility Solid solubility and temperature solubility decreases increases with increasing temperature

4 Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubilities. Suppose you have 90 g KN 3 contaminated with 10 g NaCl. Fractional crystallization: 1. Dissolve sample in 100 ml of water at 60 0 C 2. Cool solution to 0 0 C 3. All NaCl will stay in solution (s = 34.2g/100g) g of PURE KN 3 will precipitate (s = 12 g/100g). 90 g 12 g = 78 g

5 Temperature and Solubility Solubility is influenced by temperature. In warmer water, more solid will dissolve. This is because a high temperature means H 2 molecules are moving faster (keeping more solid molecules suspended). Conversely a gas will be less soluble at a higher temperature. This is because when gas molecules are moving faster they are able to escape from the liquid surface. Think of cold soda vs. warm soda. Warm soda goes flat faster.

6 Pressure and Solubility of Gases The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry s law). c = kp c is the concentration (M) of the dissolved gas P is the pressure of the gas over the solution k is a constant (mol/l atm) that depends only on temperature low P high P low c high c

7 Gases in Solution In general, the solubility of gases in water increases with increasing mass. Larger molecules have stronger dispersion forces.

8 Gases in Solution The solubility of liquids and solids does not change appreciably with pressure. The solubility of a gas in a liquid is directly proportional to its pressure.

9 Henry s Law where C g = kp g C g is the solubility of the gas; k is the Henry s law constant for that gas in that solvent; P g is the partial pressure of the gas above the liquid.

10 Temperature Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

11 Temperature The opposite is true of gases: Carbonated soft drinks are more bubbly if stored in the refrigerator. Warm lakes have less 2 dissolved in them than cool lakes.

12 Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering P 1 = X 1 P 1 0 Raoult s law P 1 0 = vapor pressure of pure solvent X 1 = mole fraction of the solvent If the solution contains only one solute: X 1 = 1 X 2 P 10 - P 1 = ΔP = X 2 P 1 0 X 2 = mole fraction of the solute

13 Fractional Distillation Apparatus

14 Boiling-Point Elevation ΔT b = T b T b 0 0 T b is the boiling point of the pure solvent T b is the boiling point of the solution T b > T b 0 ΔT b > 0 ΔT b = K b m m is the molality of the solution K b is the molal boiling-point elevation constant ( 0 C/m)

15 Freezing-Point Depression 0 ΔT f = T f T f 0 T f is the freezing point of the pure solvent T f is the freezing point of the solution 0 T f > T f ΔT f > 0 ΔT f = K f m m is the molality of the solution K f is the molal freezing-point depression constant ( 0 C/m)

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17 What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is g. m = ΔT f = K f m moles of solute = mass of solvent (kg) K f water = C/m 478 g x 1 mol g kg solvent = 2.41 m ΔT f = K f m = C/m x 2.41 m = C ΔT f = T 0 f T f 0 T f = T f ΔT f = C C = C

18 smotic Pressure (π) smosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. smotic pressure (π) is the pressure required to stop osmosis. dilute more concentrated

19 smotic Pressure (π) High P Low P M is the molarity of the solution R is the gas constant T is the temperature (in K) π = MRT

20 smotic pressure smosis is the spontaneous movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration smotic Pressure - The Pressure that must be applied to stop osmosis π = i CRT where π = osmotic pressure i = van t Hoff factor C = molarity R = ideal gas constant T = Kelvin temperature

21 smosis and Blood Cells (a) A cell placed in an isotonic solution. The net movement of water in and out of the cell is zero because the concentration of solutes inside and outside the cell is the same. (b) In a hypertonic solution, the concentration of solutes outside the cell is greater than that inside. There is a net flow of water out of the cell, causing the cell to dehydrate, shrink, and perhaps die. (c) In a hypotonic solution, the concentration of solutes outside of the cell is less than that inside. There is a net flow of water into the cell, causing the cell to swell and perhaps to burst.

22 Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. Vapor-Pressure Lowering P 1 = X 1 P 1 0 Boiling-Point Elevation Freezing-Point Depression smotic Pressure (π) ΔT b = K b m ΔT f = K f m π = MRT

23 Most concentration units are expressed as: Amount of solute Amount of solvent or solution Parts per million (ppm): grams of solute/grams of solution (then multiplied by 10 6 or 1 million) Parts per billion (ppb): grams of solute/grams of solution (then multiplied by 10 9 or 1 billion) Parts per trillion (ppt): grams of solute/grams of solution (then multiplied by or 1 trillion) ppm, ppb, ppt ordinarily are used when expressing extremely low concentrations (a liter of water that is 1 ppm fluoride contains only 1 mg )

24 Water: the Universal Solvent ne side of water is negatively charged because the oxygen atom keeps the shared electrons longer than the hydrogen atoms. As a result the oxygen side is negatively charged and the hydrogen side of water is positively charged.

25 Water: the Universal Solvent Like a magnet that pulls on things that are magnetic, water pulls on things that are electrically charged. Magnets have north & south poles, water has positive and negative poles and thus called a polar solvent. Since unlike charges attract, the negative end of water will be attracted to the positive sodium ion. The positive end of water will be attracted to the negative chloride ion. Since water is always in motion, it will pull on the ionic compound and move the ions away from each other. This dissolves the ionic compound. Na + Cl -

26 Wax does not repel water We ve heard that wax or oils repel water. But that isn t true. Water is so attracted to other water molecules that anything between them is squeezed out of the way. il droplet

27 Soaps & Detergents Soaps and detergents are chains that have one end that is like oil and has no charge and the other end is charged. S 4 - S 4 - S - 4 S - 4 S 4 - S 4 - il droplet