Separation of Salt & Sand Solubility –Salt is soluble in water, sand is not –Selective dissolving of soluble component Separation –Solution passes filter, solid sand does not Recovery –Dry solution and sand to weigh components Calculations –PerCent salt versus sand –Yield, sources of loss

Mixtures 2 or more materials, mechanically mixed –Any combination of gas, liquid, solid Humidity, water vapor in air = gas in a gas CO 2 in can of Coca-Cola = gas in a liquid Alcohol in wine = liquid in a liquid Sugar in coffee = solid in a liquid Salt and sand (e.g. Santa Cruz beach)

Mixture Properties Homogeneous –Single phase (no sediment, no cloudiness) Uniform appearance, often transparent –Every part of the material is the same Clear Lime Jell-O (no raisins) Heterogeneous –One or more phases combined Concrete (Rocks, cement, sand, water) Raisin pudding, cranberry sauce, toothpaste Cream (oil suspended in water) Butter (water suspended in oil)

Mixtures Mixtures = physical combinations –Combinations without chemical reactions Lemon Juice + water + sugar = lemonade Saltpeter + charcoal + sulfur = black gunpowder –Stable until ignited –Can be separated into constituent materials Evaporation of sea water into salts –We will do this in Salt & Sand Experiment Coffee filter passes liquid, retains solids Garbage company separates cans with magnets

Salt & Sand A heterogeneous mixture NOT a compound Can be separated by physical means –Dissolving soluble component –Filtering insoluble component –Evaporation to recover solid component Will use data to calculate recovery yield

Dissolving process Salt molecule an array of Na and Cl ions –Water forms loose bonds with both ions –“cloud” of water molecules and ions form Solid material absorbed by liquid –Limitation on dissolved amount = “Solubility” –“Unsaturated” when more could dissolve –“Saturated” when no more dissolves –“Super-Saturated” more dissolved than stable

Packing of NaCl Ions Electron Microscope Photograph of NaCl

Dissolving Salt in Water NaCl(s) + H 2 O  Na + (aq) + Cl - (aq)

Dissolving of NaCl separation + hydration of ions Timberlake, Chemistry 7 th Edition, page 287 HH O Na Cl hydrated ions

100 mL Interstitial Spaces and Particle Size Interstitial spaces (holes in water where substances dissolve) Parking at SJCC if you arrive at 7:00 AM = _____ Parking at SJCC if you arrive at 9:45 AM = _____ More available spaces if you arrive early. Salt dissolves quicker when you begin because there are more available spaces to 'park'. Analogy: Compact car is easier to park than SUV. STIR Easy Hard Theory: Crush salt to make particles smaller (increase surface area) …it will dissolve more rapidly.

Filtration Solid + Liquid mixture separated via filter … like a coffee maker. Filter stops solid phase, passes liquid Squirt bottle helps wash mixture into filter paper cone

Evaporation Salt is recovered by evaporating the water Use gentle heat to avoid splatter and loss of salt. Measure salt by weighing when dry. Measure sand by weighing when dry

Recovery Separation of Salt and Sand, 2 weights –Dry salt recovered from mixture –Dry sand recovered from mixture Sum of Salt + Sand mass = mixture mass –Difference is experimental error –% salt is mass salt / sum of salt+sand –% sand is mass sand/ sum of salt+sand –% recovery is mass salt+sand/starting mixture

Yields Output material divided by Input material –100 gm product, 200 grams start, = 50% yield Rest went “somewhere”, but not into product Excess Reactants –Exactly correct amounts may never conclude –6*10^23 is a lot of atoms Long time for last reacting atoms to find each other Boys+Girls=couples, –Odds of few singles on billions of planets getting together –The fix is excess amount of one reactant Drives reaction to completion by consuming one ingredient We will do this in the Copper Sulfide experiment

Calculations, Percentges

Use of Percentage example

Using Percentage

Percentages with Apples

Cost as Percentage Also observe sale price is 75% (100% - 25%) x $120 = $90

Can you exceed 100%?, sure! Obesity exceeds 100% of ideal weight –A multiple of ideal weight expressed as % New price is 150% of old price –Item priced at $100 raised to $150 Increase the recipe to 125% –25% more materials required –125/100 = 1.25 –125%-100% = 25%

Percent recovery

To the benches ! Substitute Saturated Salt solution for sea water