Lecture Solubility (What is the key to life?)

Have you ever made lemonade? Have you ever drank a soda pop? Have you ever drank milk? What do all these items have in common?

1. Mixture: two or more substances physically combined, not chemically combined a. homogeneous: mixture is evenly spread out: sugar cookie, lemonade b. heterogeneous: mixture unevenly spread out: chocolate chip cookie, unmixed lemonade 2. Solution: a homogeneous mixture in which the particle attraction (electrons) keep it stable ? a. all three phases can occur as a solution: alloy is solution of metals: 14K gold (w/silver); perfume too b. cannot be filtered because the particles are too small, thus… can be suspended due to solution’s atomic-kinetic energy (Brownian motion) c. made of two parts: solute and the solvent

3. Solvent: dissolves particles, usually the larger quantity by volume; lemonade = ? 4. Solute: dissolves into the solvent, usually the smaller in volume; lemonade = ? 5. Universal solvent: H 2 O a. water will dissolve so many things, especially particles which have a charge (ionic) b. polar molecule: uneven distribution of charges on the molecule; water: negative near the oxygen and positive near the two hydrogen: acts like two mini-magnets causes water to dissolve other polar molecules: acts as attachment points to grab and dissolve: + w/ - non-polar: no attachment points for water: lipids; but non-polar will dissolve non-polar: dry cleaning c. do you like Disneyland, how about Mickey Mouse?

H + H + O = H 2 O Polar molecule: HH O _ + +

d. water is shaped like a pyramid: tetrahedron e. polarity of water explains many attributes, especially that water molecules bond together via hydrogen bond (weak bond): -high surface tension: bugs can walk on water -high specific heat (due to groupings of water molecules) holds water strongly together: absorbs a lot of energy needed to break the H bonds -six sided structure when frozen: snow flakes -volume increases when frozen: less dense than liquid water -water moving up plants to the leaves: capillary action

6. Rate of dissolving due to three factors: a. temperature: high temp = faster molecules move: increased kinetic energy: faster rate of dissolving cold vs hot lemonade? b. particle size: dissolving occurs only on the surface of the solute: smaller object = the more surface area to volume: small solutes dissolve faster type of sugar for lemonade? c. solution movement: increases the energy of the system: increases the rate of dissolving to stir or not to stir the lemonade, that is the question

7. Solubility: the ability to dissolve and form a solution: a characteristic property a. can range from insoluble (sand in water) to infinitely soluble (ethanol in water) b. the maximum mass in a given volume (measured in grams) usually expressed as # of grams of solute per 100g of solvent at a specific temperature: sugar: 200g/100g water…. a lot!! salt: 36 g/100g water…. very poorly thus solubility is a characteristic property: this is due to the strength of the bond between the atoms in the compound: strong bonds = low solubility weak bonds = high solubility

Variable solubility of different substances: CHARACTERISTIC PROPERTY DRAW THIS GRAPH

c. solubility is affected by both temperature and pressure: -gases: 1. increase temp: decrease the solubility (inverse relationship): pour a soda cold or warm?, stream water for dissolved oxygen for fish? 2. increase pressure: increase solubility: soda goes flat when? -solid: 1. solubility increases with temperature (direct relationship): how would you make lemonade which is very sugary?

Variable solubility due to temperature change:

solubility of a gas:

8. Concentration: maximum amount of solute in a volume of solvent: g/cm 3 (note: it is the same unit as density but it is two different substances, unlike density). Is usually given in g/100 cm 3 : Suppose you have a solution w/ a concentration of 0.015g per 1cm 3. How many grams of solute would you have at the same concentration and the same temperature if you had 100 cm 3 of solvent?: 0.015g = Xg 1cm 3 100cm g x 100 cm 3 = Xg x 1 cm 3 = 1.5g (per 100cm 3)

a. saturated: maximum solute at a given temp and pressure: visible when a precipitate (undisolvable solute) is present at the bottom of the container (too much sugar in the lemonade). Also known as concentrated (maximum) or in equilibrium: dissolving and undissolving rates of solute are at a constant b. unsaturated: less solute than saturated; could dissolve more solute; also known as dilute

Label: -saturated -unsaturated

c. supersaturated: more solute dissolved than at saturation: rock candy. Made by increasing the solvent temperature, thus increasing the solubility, then cool the solution down and the solution is now supersaturated: very unstable and will precipitate to saturated if disturbed 9. suspension: mixture with particles so large that over time they will settle out: not enough kinetic energy in the system to keep them suspended: forms a precipitate 10. Colloid: small particles suspended by the kinetic energy of the electrons: reflect light when shined through the solution (Tyndall effect: milk).

Label: -supersaturated

Worksheet 19.2: making solutions: Example: a scientist needs to prepare one liter of a solution of potassium chloride (KCl) for an experiment. The concentration of the required solution is 3.2 Moles. How will the scientist prepare this solution from the solid KCl she has in a jar on her lab shelf? Show your work!!: know: 3.2 Moles, KCl ? know: 1L Formula: molarity = # moles solute liter of solution 1M = g solute 1 L solvent

1K x 39 amu  39g 1Cl x 36 amu  36g formula mass of solute = 75 amu molar mass of solute = 75 g 1M = g solute 1 L solvent 1M = 75g 1L So, total mass solute = 75g for 1 liter of solvent which is 1 molar; but we want what molarity? 75g x 3.2 M = 240g (in 1 liter) 1M