Download Chapter 2: Measurements and Problem Solving

CHEMISTRY 100
CHAPTER 2: MEASUREMENT and PROBLEM SOLVING
Homework problems: 27, 29, 31, 33, 37, 39, 41, 45, 47, 49, 51, 53, 57, 63, 69, 73, 77, 81, 87,
89, 91, 93, 97, 105
Outline
I.
Measurements
A. Scientific Notation (exponential notation)
B. Count vs Measurement
C. Counts and Definitions are not measurements – no uncertainty
1. Definitions not the same as conversion factors
2. Definition: 1 foot = 12 inches, 16 oz = 1 pound
3. Conversion factor 1 inch = 2.54... cm, 1 pound = 454.... g
D. Measurements have uncertainty
1.
Include all known digits plus one estimate digit
2. Significant figures
a. nonzero digits: always significant
123.41
(5 sig. figs.)
b. enclosed zeros: always significant
130.053
(6 sig. figs.)
c. leading zeroes: never significant
0.0000403
(3 sig. figs.)
d. trailing zeroes:
i.
after decimal: always significant
2.3400
(5 sig. figs.)
ii.
before decimal: can’t tell so assume not significant
2300
(2 sig. figs.)
E. Measurements have units
1. SI system
2. Metric system
a. Liter not SI but used very frequently
b. 1 cc = 1 mL
3. Derived Units (area, volume, etc.)
4. conversion factors (factor label, unit analysis, factor conversion method)
5. density and specific gravity
II. Significant Figures Revisited
A. All digits known to be correct plus one uncertain
B. Always estimate between the smallest division when measuring
C. Addition
D. Multiplication
E. Plugging numbers into a calculator does NOT make them more or less accurate
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III. More Calculations
A. Percent Calculations
1. percent = (fraction/whole) x 100
B. Density
1. density = mass/volume
C. Unit conversions
1. called dimensional analysis, factor unit method, etc.
2. cancel a unit in numerator with identical one in denominator of conversion factor
D. How to approach word problems
1. Read the problem through once. Just read it – don’t try to solve it in 1 step
2. Determine what the questions is asking – this is usually at the end right
before the question mark.
3. Inventory your available information – what info do you have?
4. Plan how to get from what you have to what the question is asking
5. Set up the problem according to your plan map
6. do unit analysis (factor label method)
7. check for sig figs
8. plug numbers into calculator
Chapter Objectives
Knowledge
Recognize the SI units and its abbreviation (g and m) for mass and distance.
Memorize the prefixes mega-, kilo, centi-, milli-, and microMemorize formula for density (D = m/V)
Recall what specific gravity is
Comprehension
Use scientific notation to show correct number of significant figures
Determine how many sig figs a number does have, and how many it should have
Application
Do calculations (addition/subtraction and multiplication/division) using the
correct number of significant figures
Analysis
Demonstrate the ability to do dimensional analysis with any conversion factors
Solve problems involving multiple conversion factors
Given any two of density, mass, and volume, be able to find the third
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