Unit 2 – Lecture 2

Composition Pure Substance follow exact measures or proportions made up of only one kind of particle Mixtures Can be any amounts or kinds of particles

Pure Substances Elements found on the Periodic Table made of only one kind of atom all atoms of an element are the same examples?

Pure Substances – cont’d Compounds two or more atoms chemically combined follows a formula cannot be separated except: by chemical means [forms a new compound]

Element or Compound? oxygen [O2] carbon dioxide [CO2] sodium chloride [NaCl] calcium [Ca+] carbon tetrachloride [CCl4]

Mixtures Two Types homogenous “homo” – the same “genous” – kind, or type heterogenous “hetero” – different

Mixtures – cont’d Homogenous Mixture the same throughout particles so small or so well mixed that the particles can’t be seen aka solutions

Solutions aka Homogenous Mixture made of any phase in any other phase solid in liquid, gas in liquid, etc.

Solutions – cont’d have two parts: solute – substance being dissolved, usually in less amount solvent – substance doing the dissolving, usually in greater amount it is not possible to distinguish solute from solvent if in solution

Solutions – cont’d Soluble – substance can be dissolved in a given solvent ex: sugar in water Insoluble – substance cannot be dissolved in a given solvent ex: sand in water

Practice If air is 78% Nitrogen and 21% Oxygen, which is the solvent? What is the solute in soda pop? Which is the solvent in sweet tea? What is the solute in muddy water?

Types of Solutions Alloy solutions of metals ex: brass [zinc + copper], steel [iron + carbon], sterling silver [silver + copper] Amalgam – solution in Mercury (liquid metal) ex: silver + mercury = used in dentistry Aqueous Solutions – uses water as the solvent

Types of Solutions – cont’d Concentrated high ratio of solute to solvent Dilute low ratio of solute to solve

Making a Solution “Surround and Separate” particles of the solvent pull particles of solute into solution

Making a Solution – cont’d Speeding up the making of a solution: agitation stirring/shaking makes particles collide more often increase surface area grinding up a solute makes it easier to “surround and separate” them into solution

Making a Solution – cont’d Speeding up the making of a solution: increase temperature heating a solution speeds up the particles, increasing the number of collisions NOTE: When dissolving a gas in a liquid, a colder liquid slows down the gas particles and dissolves more total gas

Agitation, Temp, or Surface Area? Which method of speeding up a solution explains why a powdered aspirin works faster than a tablet? Which method of speeding up a solution explains why sugar dissolves better in fresh tea than iced tea? Which method of speeding up a solution explains why Kool-Aid powder has to be stirred into water? Which method of speeding up a solution explains why soup mix dissolves faster than bouillon cubes?

Amounts of Solute Solubility – how well a substance will dissolve in 100g of water at a given temperature differs with each substance and temperature

Saturation of Solute Unsaturated more solute can be dissolved in solution Saturated no more solute can be dissolved in solution Saturation Point – point at which saturation happens

Saturation of Solute – cont’d Supersaturated more solute than solvent can typically hold is dissolved – due to temperature or other change after temp decreases, excess solute may stay in solution excess solute will come out of solution if disturbed until it reaches the saturation point called precipitate, or may form crystals

Saturation of Solute – cont’d Supersaturation – How we make Rock Candy!

Using the chart, how can I find out when a certain solution is saturated, unsaturated, or supersaturated?

the line tells me the saturation point at each temperature above the line, the solution has more solute than the saturation point [solution is supersaturated] below the line, the solution has less solute than the saturation point [solution is unsaturated]

Heterogeneous Mixtures Heterogenous Mixtures mixtures that are not well mixed [not the same throughout] often, particles are so large that they can be seen or “picked out” ex: sand in water

Heterog. Mixtures – cont’d Two types: Suspensions temporary mixtures particles settle out upon standing ex: mud [water w/ soil, clay, or silt], paint, flour in water…

Heterog. Mixtures – cont’d Two types: Colloids particles do not settle out – they are suspended, but not dissolved appears as a homogeneous mixture, but the particles scatter light (Tyndall Effect) ex: milk, fog, mayo, smoke, blood…

Heterog. Mixtures – cont’d Tyndall Effect – scattering of light through the particles of a colloid ex: can see flashlight beam through fog or dusty air

Homework correct warmup complete homo/hetero w/s on page 5 begin making flashcards to memorize elements on page 12 I can start quizzing you on the first 10 in 2 days…