2. Announcements
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Attendance
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Sign up on Connect. First assignment due at 8pm
on next Monday.
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PS1 due next Thursday.
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Postlab (Expt 4, 5) and prelab (Expt 6) due next
Friday.
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Evac route, campus safety goo.gl/lx8WTF
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Fire extinguishers, goo.gl/1iC7VM
3. Systematic Approach to Solving Chemistry Problems
• State Problem
• Plan
• Solution
• Check
• Comment
• Follow-up Problem
Clarify the known and unknown.
Lay out the steps from known to unknown.
Prepare a visual summary of steps
that includes conversion factors,
equations, known variables.
4. Sample Problem 1.8 Converting Units of Temperature
PROBLEM: A child has a body temperature of 38.7°C, and normal body
temperature is 98.6°F. Does the child have a fever? What is
the child’s temperature in kelvins?
PLAN
:
We have to convert °C to °F to find out if the child has a fever.
We can then use the °C to Kelvin relationship to find the
temperature in Kelvin.
SOLUTION:
Converting from °C to °F
9
5
(38.7 °C) + 32 = 101.7 °F
Converting from °C to K 38.7 °C + 273.15 = 311.8 K
Yes, the child has a fever.
5. How Many Ribosomes can Dance
on the Tip of a Hair?
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Ribosome: a ball-
shaped protein with a
5 nano-meter radius
●
A strand of human
hair is about 10.
micro-meter thick
Q: Roughly how many
ribosomes can stand
on the tip of a hair?
How many football
stadiums do we need to
fit that number of
people?
6. Sample Problem 1.7 Calculating Density from Mass and Length
PROBLEM: Lithium, a soft, gray solid with the lowest density of any
metal, is a key component of laptop and smartphone
batteries. A slab of lithium weighs 1.49 x 103
mg and has
sides that are 20.9 mm by 11.1 mm by 11.9 mm. Find the
density of lithium in g/cm3
.
PLAN: Density is expressed in g/cm3
so we need the mass in g and
the volume in cm3
.
10 mm = 1 cm
divide mass by volume
Lengths (mm) of sides
Lengths (cm) of sidesMass (mg) of Li
Mass (g) of Li
103
mg = 1 g
Volume (cm3
)
multiply lengths
Density (g/cm3
) of Li
7. Sample Problem 1.7
SOLUTION:
Similarly the other sides will be 1.11 cm and 1.19 cm, respectively.
Volume = 2.09 cm x 1.11 cm x 1.19 cm = 2.76 cm3
= 0.540 g/cm3
= 1.49 g1.49 x 103
mg x
10-3
g
1 mg
= 2.09 cm20.9 mm x
1 cm
10 mm
Density of Li =
1.49 g
2.76 cm3
8. A blast from the past
●
Suppose 20.% of the asteroid turned to dust
and spread uniformly over the Earth surface, the
dust amounted to 0.02 g per cm^2 on the
surface, and the asteroid had a density of 2
g/cm^3. Estimate the radius of the asteroid in
miles.
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Assume the Earth is a sphere with radius 6400
kilometers
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From J. Harte, Consider a Spherical Cow
9. Learning goals
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Give a chemical definition of element, and comment on the
distinction between the terms atom and element.
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Describe, in your own words, the Laws of Chemical Change:
mass conservation, constant composition, and multiple
proportions.
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Explain how these laws follow from Dalton's atomic theory.
10. Learning goals
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Describe Rutherford's alpha-ray scattering experiment and how it led to the
present model of the atom.
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Define atomic number and mass number, and explain the relation between
them.
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Define isotope, and write the symbol for an atom of a given element and
given number of neutrons.
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Explain the purpose of a mass spectrometer and its general principle of
operation.
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Describe the atomic weight scale.
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Find the molecular weight or formula weight from a chemical formula.
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Define the unified atomic mass unit, and write out the mass numbers of the
proton, neutron, and electron.
11. Lab 2 agenda
Watch the safety video
Watch the pipet video
Assign lockers
Safety quiz hand-in
Equipment list hand-in
How to use a spreadsheet program
