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

• CO2 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 MicroscopePhotograph of NaCl

Dissolving Salt in Water

NaCl(s) + H2O Na+(aq) + Cl-(aq)

Cl-

ions

Na+

ions Water molecules

Dissolving of NaClseparation + hydration of ions

Timberlake, Chemistry 7th 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 youbegin 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 PercentageAlso 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

content content content

Container + Salt & Sand 150.00 grams container + dried Salt 129.5 grams container + dired sand 124.800 grams

Emptiy Continer 100.00 grams Empty Container 100.0 grams Empty Continer 105.000 grams

50.00 Mass of Salt 29.50 grams Mass of Sand 19.80 grams

Salt recovery 29.50 grams Original Salt & Sand 50.00 grams

Sand recovery 19.80 grams Recovered Salt & Sand 49.30 grams

Total Recovery 49.30 grams fraction recovered 0.986

PerCent recovery x 100 98.6%

To the benches !

• Substitute Saturated Salt solution for sea water