Chem10171 day1
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Transcript of Chem10171 day1
CHEM 13171
Who should take it?Anyone who…• Feels anxious about
heavy first-year load as science or EG major
• Feels anxious about college chemistry
• Wants to develop good college-level study skills
Who should wait till organic?
Anyone who…• Had a 5 on AP
Chemistry test
Why study chemistry?
Combustible materials contain phlogistonSome more (charcoal), some less (metal)
Burn charcoal in closed container
Fire goes out
Why does phlogistonneed air?
Air gets saturatedwith phlogiston
Some things burn more than othersObservation
Why?Ask Questions
Pose an explanation
Burn metalTry SomethingTry Something
Observation Forms calx whichweighs more than metal
Observation
Ask QuestionsHow can the
loss of phlogistonincrease the mass?
Ask Questions
Phlogiston hasnegative mass
Pose an ExplanationPose an Explanation
Observation
Ask questions
Pose an explanation
Try something
If new observation
Ask more questions
Pose additional explanations
Heated Hg calx and got Hg and gasTotal mass of Hg & gas = mass Hg calx
Heated Hg with gas and got Hg calxMass Hg calx = total mass of Hg & gass
Observation
Why?Ask Questions
Heating Hg with gas caused the two tocombine into the calx; heating the calxcaused it to break into Hg and the gas
Pose an explanation
Burn Hg in closedcontainer then lightcandle in container
Try Something
Candle goes out
Observation
Ask Questions
Is this consistent with previousobservations & explanations?
Yes
Propose a theory
No
Revise
Observation
(Ask questions)
Hypothesis
Experiment
Observation
Ask more questions
Propose a theory
Revisehypothesisas needed
Further experiments
Revise theoryas needed
MODERN SCIENTIFIC METHOD
What is chemistry?
• The study of matter and its properties, the changes that matter undergoes, and the energy associated with those changes. (MSS, p. 4)
• The study of matter and its properties, the changes that matter undergoes, and the energy associated with those changes. (MSS, p. 4)
• Matter – anything that has mass & volume
Properties & Changes
If you combine A&Band get C, is this achemical change orphysical change?
Chemical changebecause the Substanceshave changedcomposition.
Properties & Changes
If you combine A&Band get D, is this achemical change orphysical change?
Chemical changebecause the Substanceshave changedcomposition.
Properties & Changes
If you change theconditions C andget D, is this achemical change orphysical change?
Physical changebecause the Substanceshave changedcomposition.
Properties & Changes
If you change theconditions C andget D, does D havedifferent propertiesthan C?
Same chemicalproperties b/c it’sthe same substance.Different physicalproperties b/c it’s ina different form.
Properties & Changes
Are there chemical or physical changesbetween A and B?
CC: 3Y2 + 3R -> RY2 (new composition)CC: 3R + 3B -> 3RB (new composition)PC: 3B(s) -> 3B(g)
Properties & Changes
• Aluminum foil is cut in half• Clay is molded into a pot• Milk goes sour• Water in an ice cube tray freezes• Food scraps are composted• Rubbing alcohol evaporates in your
hand• Hydrogen peroxide bubbles in a cut
PPCPCPC
Properties & Changes
• Can we make some generalizations about chemical and physical properties and changes?
Energy
(b)
Two states of the samesystem are shown as (a)and (b).
Where does eachstate belong in the PEdiagram?
Where does the PE gowhen it is lost from the state with higher PE?
Energy
Measuring
What is the length of the metal strip?(a) 7.5 cm (b) 7.25 cm (c) 7.4 cm (d) 7.45 cm
In science, we use significant figures – all the digits you canread plus the first digit that you can estimate.
Density
DW = 1.0 g/mL, DC = 0.88 g/mL, DA = 1.4 g/mLWhich is a possible density for B? (a) 0.79 g/mL (b) 0.86 g/mL (c) 0.94 g/mL (d)1.2 g/mL
DW = 1.0 g/mL, DC = 0.88 g/mL, DA = 1.4 g/mLWhich is a possible density for B? (a) 0.79 g/mL (b) 0.86 g/mL (c) 0.94 g/mL (d)1.2 g/mL
Density = M/V units: g/mL
DC < DBDB < DWDW < DA
You have 3 pieces of metal each having the same mass.You drop each into one of three graduated cylinders eachof which started with 25.0 mL of water.Which metal is the most dense?
V = 3.2 mL V = 2.9 mL V = 3.5 mL
D = M/V division by the smallest V will give the biggest D
If the mass of B is 25.0 g, what is the density of B?(a) 8.6 g/mL (b) 8.62 g/mL (c) 8.621 g/mL (d) 8.6207 g/mL
A 25.0 g sample ofwater was measuredfour times by fourdifferent students.Which student(s) was(were)precise in his/hermeasurements?Which was (were) accurate?
A B
DC
The volume of abox is length xwidth x height:V=LWHWhat is the volume of this box?(f)10000(g)100000(h)1
1m
100cm
100cm
The volume of abox is length xwidth x height:V=LWHWhat is the volume of this box?•10000•100000 cm3
•1 m3
1m
100cm
100cm
-Apples/oranges-Canceling units-Converting units
p. 18-21
Re-cap
• Modern scientific method• Definition of chemistry• Understanding of some basic concepts:
physical chemical properties/changes, energy, density, measurements – significant figures, accuracy/precision, units
