Chemistry
Notes
Unit 2 Measurement
Metrics
Scientific Notation
Uncertainty
Metric Measurement
 Fundamental – deals with single
measurements that describes a single
phenomenon
 Ex: time, distance, mass
 Derived – deals with two or more
measurements that describe a single
phenomenon
 Ex: m/s, Kg*m/s2, m/s2, N*m
SOME REVIEW FOR YOU
 The metric system is much easier than our
standard system of measurement because
units with in the metric system are powers
of ten.
 Ex: convert 1200 g to kg
 Answer  1.20 kg (just move the decimal)
 Ex: convert 40 oz.  lbs
 Answer  2 ½ lbs (have to do some math)
SOME REVIEW FOR YOU
Metric Measurement
 Some basic units  see table 2.1 on page 29
 Length  meters
 Time  seconds
 Mass  kilogram
 Metric Prefixes  see table 2.2 on page 29





MicroMillCentiDeci Kilo-
0.000 001 m
0.001 m
0.01 m
0.1 m
1000 m
SOME REVIEW FOR YOU
 Converting between metric units
 Remember
 SSL (Smaller units to larger units move
decimal to the left)
 K,H,D,b,d,c,m
 E.g. When you convert from milli- to deci- you
move the decimal point two places
SOME REVIEW FOR YOU
 Conversion with Unit Analysis Method:
 Used to convert standard to metric
 Standard form below:
## given units ## desired units = desired units
## given units
 If set up correctly, the given units will cancel
out. That how you know you set it up right.
SOME REVIEW FOR YOU
Mass = the amount of matter in an object
 Measured in kilograms (kg)
 Not to be confused weight. Weight is more
comparable to force,
 W = mg
 A balance is an instrument used to
determine mass
SOME REVIEW FOR YOU
 Mass v. Weight
REVIEW
 Length = the distance covered by a straight
line segment between two points
 Measured in meters (m)
 Time – interval between two occurrences
 Measured in seconds (s)
SOME REVIEW FOR YOU
Temperature = the average kinetic energy of
the particles that make up matter.
 Measured in Kelvin (K)
 Kelvin is a scale based on molecular motion.
 We also use Celsius (oC)
 To convert from (oC) to K:
 K = 273.15 + (oC)
 (oC) = K – 273.15
SOME REVIEW FOR YOU
Example problem: convert 25oC to Kelvin
 298 K
Example problem: convert 400 Kelvin to oC
 127 oC
SOME REVIEW FOR YOU
Scientific Notation
 Used in science because
scientist often work with very
large or very small numbers
 Ex: Astronomers,
Bacteriologists, Chemists
SOME REVIEW FOR YOU
 To add and subtract numbers that are in
scientific notation you have to:
 Be sure numbers are in the same units
 NOT one in grams and one in kilograms
 Be sure the numbers are to the same power
 Examples:
 2.30 X 1016 + 3.44 X 1014 = __________
 1.14 X 107 – 3.11 X 109 = __________
SOME REVIEW FOR YOU
 To multiply or divide numbers that are in
scientific notation you have to:
 Add exponents if you are multiplying
 Subtract exponents if you are dividing
 Examples
 (6.87 X 1087) (8.24 X 1073) = _________
 (4.87 X 1036) / (8.55 X 1021) = ________
HOMEWORK
 GCWS 2A
(More) Uncertainty
 Recall: in chemistry (or any science) we
deal with a lot of uncertainty.
 Question: how else do we handle
uncertainty?
 Answer: Calculations like percent error
and significant digits allow scientist to see
how far off they may be.
Uncertainty
Percent Error: is calculated as seen below
Percent Error =
Experimental value – Theoretical value X 100
Theoretical value
 Because absolute value is used % error
will always be a positive number.
Uncertainty
Ex: what is the % error of an experiment where a
student produces 43 g of sodium sulfite from the
reaction including sodium, sulfur and oxygen? The
theoretical mass of sodium sulfite was 49.2 g.
 12.6 %
Ex: what is the % error of an experiment where a
student observed that the time a certain reaction lasted
was 15.24 s? The theoretical time that was calculated
was 15.01 s.
 1.53%
MORE HOMEWORK
 DO GCWS 2C
Uncertainty
 What is the measurement below?
11.65 cm
Uncertainty
 All measurements are approximates.
 Sig figs allow us to be honest about how precise are
measurements are
 Example
Postage Scale: 3 g - precise to 1 significant figure
Two-pan balance: 2.53 - precise to 3 significant figures
Analytical balance: 2.531 - precise to g 4 significant figures
 As we improve the sensitivity of the equipment
used to make a measurement, the number of
significant figures increases.
Uncertainty
Significant Figures
 Question: Which of the following
measurements is the most precise?
 12.000 m
 12 m
Uncertainty
 Answer: 12.000 m is more precise because
what is being said is that this measurement was
to the closest 0.001 m opposed to being
measured to the closest meter.
 These numbers are not saying the same thing.
 12.000 is saying the measurement is between 11.999
m and 12.001m
 12 is saying the measurement is between 11.5 m and
12.5 m
 12.000 contains 5 significant digits whereas 12 only
contains 2
 All numbers but the last ones are certain.
Uncertainty
Determining Significant digits:
 All non-zero numbers are significant
 95.32  4 sig figs
 Zeros after decimal points are significant
 54.100  5 sig figs
 Zeros between non-zero numbers are significant
 120.0000001  10 sig figs
 Zeros that are place holders are not significant
 0.000045  2 sig figs
 0.001000  4 sig figs
Uncertainty
 Adding and subtracting significant figures
 Answer should have as many decimal
places as the measured number with the
smallest number of decimal places.
 EX:
Uncertainty
 Multiplying and Dividing with significant
figures
 answer should have as many significant
figures as the measured number with the
smallest number of significant figures.
 Ex:
Summary
 What questions do you still have?
 What was unclear?