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