Accuracy, Precision, Percent
Error, & Temperature Scales
Accuracy
• How close a measured value is to an
accepted value
-Accuracy can be determined by just on
measurement
-Depends on the quality of the measuring
device
The density of water is 1.00 g/mL
1.03
.98
1.01
1.00
.99
Precision
•How close a series of measurements are
to one another
-Precision is determined by more than one
measurement
-Depends on the skill of
the person measuring
The density of water is 1.00 g/mL
.89
.87
.89
.88
.88
Accuracy or Precision?
The boiling point of
water is 100°C
The atomic mass of
carbon is 12 amu’s
89°C
11.95 amu’s
91°C
12.01 amu’s
90°C
11.97 amu’s
91°C
11.98 amu’s
80°C
12.03 amu’s
Accuracy or Precision?
The electronegativity
of Fluorine is 3.8
The evaporation
temperature of isopropyl
alcohol is 83°C
2.1
91°C
1.6
89°C
3.5
90°C
2.8
89°C
4.2
90°C
Percent Error
• Accepted Value (also known as theoretical value)
- a quantity used by general agreement of
the scientific community
- “what you are supposed to get”
• Experimental Value (also known as the actual value)
- a quantitative value measured during an
experiment
- “what you got”
Percent Error
Error = the difference between the accepted
value and the experimental value
Percent Error = the percent that a measured
value differs from an accepted value
% Error = (What you got) – (What you were supposed to get) x 100
(What you were supposed to get)
Percent Error Practice
1. The boiling point of water is 100°C. During an
experiment, water came to a boil at 97°C according to
the thermometer that was being used. What is the
percent error of the thermometer?
2. An experiment was performed to determine the density
of water. The results of the experiment showed that
water had a density of 1.15 g/mL. What was the
percent error in this experiment?
Percent Error Practice
3. An experiment was conducted to find the mass of one
mole of carbon atoms. The results of the experiment
showed that a mole of carbon atoms had a mass of
15.78 g. The accepted value of a mole of carbon atoms
is 16.00 grams. What is the percent error in this
experiment?
4. An experiment performed to determine the density of
lead yields a value of 10.95 g/cm3. The accepted value
for the density of lead is 11.342 g/cm3. Find the
percent error.
Percent Error Practice
5. Find the percent error in a measurement of the
boiling point of bromine if the laboratory figure is
40.6°C and the accepted value is 59.35°C.
Temperature Scales
Relationship
between the
Fahrenheit, Celsius,
and Kelvin Scales
The Fahrenheit Scale
This is the temperature scale that
you are probably most familiar with,
living in the United States. When
you listen to the weather report on
TV, the Fahrenheit scale is used.
The thermometers that you have in
your house, for use as; swimming
pools, cooking, bath tubs, or reading
body temperature, are all likely to be
in Fahrenheit. In Canada and most
other countries, the news will report
the temperature on the Celsius
Scale.
The Celsius Scale
The Celsius scale is commonly used for scientific work.
The thermometers we use in our lab are marked with
the Celsius scale. The Celsius scale is also called the
Centigrade scale because it was designed in such a way
that there are 100 units or degrees between the freezing
point and boiling point of water. One of the limitations
of the Celsius scale is that negative temperatures are
very common.
Since temperature is a measure of the kinetic energy of
molecules, this would also suggest that it is possible to
have less than zero energy. This is why the Kelvin scale
was necessary.
The Kelvin Scale
The International System of
Measurements (SI) uses the
Kelvin scale for measuring
temperature. The Kelvin scale
is based on the concept of
absolute zero, the theoretical
temperature at which molecules
would have zero kinetic energy.
Absolute zero, which is about 273.15°C, is set at zero on the
Kelvin scale.
A Comparison of
Temperature Scales
Set Points
Fahrenheit
Celsius
Kelvin
Water Boils
212
100
373
Body
Temperature
98.6
37
310
Water Freezes
32
0
273
Absolute Zero
-460
-273
0
Temperature Conversion
Formulas
Conversion
Formula
Example
Celsius to Kelvin
K = C + 273
21°C = 294K
Kelvin to Celsius
C = K – 273
313K = 40°C
C =(F-32) x 5/9
89°F = 31.7°C
Celsius to Fahrenheit F =(Cx9/5) + 32
50°C = 122°F
Fahrenheit to Celsius