Sections 1'3, 1'4, and 1'5

1
Lecture 2

• Sections 1.3, 1.4, and 1.5

2
Memorization Assignment

• Symbols for the quantities Mass, Length, Time,
  Temperature, and Amount of Substance
• m, l, t, T, n
• Basic units for these quantities
• kilogram, meter, second, kelvin, mole
• Symbols for the basic units
• kg, m, s, K, mol

3
Fundamental SI Quantities and Their Basic Units

• Mass m
• Length l
• Time t
• Temperature T
• Electric current I
• Amount of substance n

• Kilogram kg
• Meter m
• Second s
• Kelvin K
• Ampere A
• Mole mol

4
Memorization Continued

• Symbols for metric prefixes giga, mega, kilo,
  deci, centi, milli, micro, nano, pico
• G, M, k, d, c, m, µ (mc), n, p
• Meanings of these prefixes
• 109, etc.

5
Section 1.3

• Discussion Questions
• What two parts does a measurement consist of?
• See page 8
• What is the difference between mass and weight?
• See page 10

6
The SI (Modern Metric System)

• Combines prefixes with basic units
• Basic unit of mass already has a prefix
• 1 Gm 109 m, 1Gs 109 s, etc.
• 1 pg 10-12 g, or 1012 pg 1 g
• But NOT 10-12 pg 1 g!
• This is a metric world. Live with it.
• Its absolutely essential that you be fluent in
  metric.

7
Volume Units

• Cubic length m3, dm3, cm3, etc.
• We do the same in our system
• Cubic inches, cubic yards, etc.
• Other volume units L, mL, etc.
• We do the same in our system
• Cups, pints, quarts, gallons, teaspoons, fluid
  ounces, etc. etc.
• Easy correspondence in metric system
• 1 L 1 dm3, 1 mL 1 cm3

8
Visualizing Metric Units

• Length of a pencil
• 15 mm? 15 cm? 15 dm? 15 m?
• Mass of a sirloin steak
• 200 mg? 200 g? 200 kg?
• Dose of cough medicine
• 10 µL? 10 mL? 10 cm3? 10 L?

9
Section 1.4

• Discussion Questions
• In a measurement, how many numbers are certain
  and how many are uncertain?
• See page 11
• What do we mean by accuracy?
• See page 12
• What do we mean by precision?
• See page 12

10
Accuracy and Precision

• Accuracy
• How close is your measurement to the correct
  answer?
• error (exp val true val)/true valx100
• Correct equation in Challenge Problem 83
• Precision
• How close are your repeated measurements to each
  other?
• Standard deviation (see p. A11)
• You do not need to know this equation
• STDEV in Excel

11
Section 1.5

• Discussion Question
• What are the two kinds of exact numbers?
• See page 13

12
Exact vs. Inexact Numbers

• All measurements are uncertain
• Only defined or counted numbers are exact
• How tall are you exactly?
• Exactly how many eggs are in a dozen eggs?
• Exactly how many cm are in an inch?
• Which of these exactlys makes sense?

13
Significant Figures

• Do not apply to exact numbers
• When are zeroes significant?
• Leading zeroes are never significant
• 0.0025 2 significant figures
• Captive zeroes are always significant
• 1.0025 5 significant figures

14
Trailing Zeroes

• Significant if number contains a decimal point
• 100. 1.00 x 102 3 significant figures
• Assumed not significant if no decimal point.
• 25,000 2 significant figures
• What if the first zero were significant?
• Write it 2.50 x 104

15
Rounding Results of Calculations

• Do like Zumdahl says, not like Zumdahl does!
• Page 15
• This is absolutely ridiculous
• Text rounds after each calculation
• Text tells you to round at the end
• Your answers often will differ from answers in
  text and solutions manual

16
Multiplication and Division

• Round result to the least number of significant
  figures in the measurements used
• Ignore exact numbers for rounding purposes
• 25.43 cm x 4.2 cm ?
• 110 cm2
• 107.565 g/25.12 mL ?
• 4.282 g/mL

17
Addition and Subtraction

• Round result to the least number of decimal
  places in the measurements used
• Ignore exact numbers for rounding purposes
• 10.656 cm 4.2 cm ?
• 14.9 cm
• 81.63 cm 2 cm ?
• 80. cm (assuming the 2 cm is a measurement)
• 4.3 x 105 cm 2.1 x 102 cm ?
• 4.3x105 cm
• 68.46 g 8.46 g ?
• 60.00 g

18
Remember Order of Operations

• (75.9 g 72.3 g)/3.52 mL ?
• 1.0 g/mL
• (1.05 1.08)/1.08x100 ?
• -3