unit 2 – lecture 2. composition pure substance follow exact measures or proportions made up of...

Unit 2 – Lecture 2

CompositionPure Substance

follow exact measures or proportionsmade up of only one kind of particle

MixturesCan be any amounts or kinds of particles

Pure SubstancesElements

found on the Periodic Tablemade of only one kind of atomall atoms of an element are the sameexamples?

Pure Substances – cont’dCompounds

two or more atoms chemically combinedfollows a formulacannot 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]

MixturesTwo Types

homogenous“homo” – the same“genous” – kind, or type

heterogenous“hetero” – different

Mixtures – cont’dHomogenous Mixture

the same throughout particles so small or so well mixed that

the particles can’t be seenaka solutions

Solutionsaka Homogenous Mixturemade of any phase in any other phase

solid in liquid, gas in liquid, etc.

Solutions – cont’dhave 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’dSoluble –

substance can be dissolved in a given solvent

ex: sugar in water

Insoluble – substance cannot be dissolved in a given

solventex: 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 SolutionsAlloy

solutions of metalsex: 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’dConcentrated

high ratio of solute to solvent

Dilutelow ratio of solute to solve

Making a Solution“Surround and Separate”

particles of the solvent pull particlesof solute into solution

Making a Solution – cont’dSpeeding up the making of a solution:

agitationstirring/shaking makes particles

collide more oftenincrease surface area

grinding up a solute makes it easier to “surround and separate” them into solution

Making a Solution – cont’dSpeeding up the making of a solution:

increase temperatureheating a solution speeds up the particles,

increasing the number of collisionsNOTE: 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 SoluteSolubility – how well a substance will dissolve

in 100g of water at a given temperaturediffers with each substance and

temperature

Saturation of SoluteUnsaturated

more solute can be dissolved in solution

Saturatedno more solute can be dissolved in solutionSaturation Point – point at which saturation

happens

Saturation of Solute – cont’dSupersaturated

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 pointcalled precipitate, or may form crystals

Saturation of Solute – cont’dSupersaturation – 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 MixturesHeterogenous 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’dTwo types:Suspensions

temporary mixturesparticles settle out upon standingex: mud [water w/ soil, clay, or silt],

paint, flour in water…

Heterog. Mixtures – cont’dTwo 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’dTyndall Effect –

scattering of light through the particles of a colloidex: can see flashlight beam through fog or

dusty air

Homeworkcorrect warmup

complete homo/hetero w/s on page 5begin making flashcards to memorize

elements on page 12I can start quizzing you on the first 10 in 2

days…