CH100A Assumptions:
No previous chemistry
Knowledge of Algebra
Read and follow the suggestions in the course syllabus.
Chemistry:
The study of the properties, reactions and composition of matter and
its relationship to energy.
Matter:
Anything that has mass and occupies space.
Mass:
Mass is a quantitative measure of inertia. Inertia is the tendency
of an object to remain at rest or in motion unless acted upon by an outside
force. Mass (unlike weight) is independent of gravity.
Weight:
Weight is a measure of the gravitational force.
Energy:
Energy is the ability to do work.
Nature manifests itself as either matter or energy. Can you name anything
that is
neither matter or energy?
Fields of Chemistry
MEASUREMENT AND NUMBERS
Two kinds of numbers
(1) Defined numbers (5280 feet = 1 mile) and counts, those values that
can be known exactly.
(2) Measured numbers (Your instructor weighs 180 pounds) which always
involves some degree of uncertainty.
Two kinds of Errors:
(1) Random errors - resulting from an uncontrolled experimental variable.
Example: An air current near a sensitive
balance.
(2) Systematic errors - resulting from a controllable experimental
variable.
Example: Use of a set of old tarnished
weights with your balance.
Precision vs Accuracy
Precision has to do with the reproducibility of a measurement.
Accuracy has to do with how close a measurement is to the true value.
Measurements are never taken to be exact.
A reported measurement should contain two kinds of information:
(1) magnitude
(2) an indication of precision or uncertainty
Significant figures = The known digits in a measurement plus
one doubtful digit.
The magnitude of uncertainty is assumed to be one in the doubtful digit.
Sig. Fig. Guidelines
(1) All nonzero digits (1 through 9) are significant.
14.7 g 3 sig. figs.
1222 lb 4 sig. figs.
(2) Leading zeros are not significant.
0.0073 in. 2 sig. figs.
(3) Confined zeros are significant.
3.006 L 4 sig. figs.
107 miles 3 sig. figs.
(4) Trailing zeros are significant (1)when there is an expressed decimal
point
on the paper or (2) they carry overbars.
6.60 g 3 sig. figs.
10.00 g 4 sig. figs.
400 g 1 sig. fig.
400. g 3 sig. figs.
Rounding Off
Experimental measurements are often not an end result but are combined
in calculations. Calculations can not improve precision.
Calculate the floor area of a room that is 17.1 feet wide and 22.2 ft. long.
Area = length x width = (17.1 ft)(22.2 ft) = 379.62 ft2 = 380. ft2
Rules for Rounding Off Significant Figures
(1) In multiplication and division the answer is rounded off to the
same number of
sig. figs. as is contained in the measurement with the least number
of significant figures.
17.2 g / 33 mL = 0.5212121 = 0.52 g/mL
77.60 mile / 22.3 hr = 3.4798 = 3.48 mi/hr
(17.0 in)(3.002 in)(330 in) = 16841 in3 = 17000 in3
(2) The results of addition and/or subtraction should be rounded off to the column containing the doubtful digit with the largest absolute value.
29.21 ft
276.50 oz
+ 74.1 ft
-32 oz
+ 7.666 ft
244.50 oz
110.976 ft
244 oz
111.0 ft
Scientific Notation = Exponential Notation
In Scientific Notation a number is expressed as the product of a number between one and ten (including one) times a power of ten. This notation is particularly useful in dealing with very large and very small numbers.
103 = 10 x 10 x 10 = 1000
102 = 10 x 10 = 100
101 = 10 = 10
10o = 1 = 1
10-1 = 1/10 = 0.1
10-2 = 1/100 = 0.01
10-3 = 1/1000 = 0.001
10500 = 1.05 x 104
70.2 = 7.02 x 101
0.00000797 = 7.97 x 10-6
0.0030 = 3.0 x 10-3
Math using Scientific Notation
(6 x 10a)(3 x 10b) = 18 x 10a + b
(6 x 106)(3 x 104) = 18 x 1010 = 1.8
x 1011
(4 x 106)(3 x 10-4) = 12 x 106-4 =
1.2 x 103
(6 x 10a)/(3 x 10b) = 2 x 10a-b
(6 x 106)/(3 x 104) = 2 x 102
(8 x 106)/(2 x 10-4) = 4 x 1010
(6 x 10a) + (3 x 10a) = 9 x 10a
(6 x 107) + (3 x 107) = 9 x 107
(6 x 10b) - (2 x 10b) = 4 x 10b
(6 x 10-14) - (3 x 10-14) = 3 x 10-14