# Graphing and measurements

```Graphing
Graphing
a. Circle graph (also called pie chart)
Used to show parts of a fixed whole. Usually parts are labeled as
percents with the circle representing 100%.
Graphing
b. Bar graph- good for showing quantitative data or
data that you can count at exact intervals
Graphing
 Line graph- good for showing relationship between
two variables
Independent variable is plotted on the X axis
 Dependent variable is plotted on the Y axis
Best fit line is drawn so that as many points fall above the line as
below

Graphing
 Directly related
 Positive slope
 As X increases, Y increases
Graphing
 Inversely related
 Negative slope
 As X value increases, Y decreases
Experimental Design
 Must be carefully designed and conducted
variable- change on purpose
 Y-Axis- dependent variable- changes in response
 Constant- all other variables do not change
 Control- standard used for comparison

X-Axis- independent
Gathering Information
 Qualitative- subject to opinion, subjective
 5 senses
See – What color or color changes, bubbles forming, solid
forming, shape size, etc.
 Hear – noise: Fizz, pop, boom, etc.
 Touch
 Feels hot – Gives off heat ~ exothermic
 Feels cold – Takes in heat ~ endothermic
 Taste – Never taste chemicals in the lab…
 Smell – is a smell produced? Waft to find out.

 Quantitative - Numerical values, objective
 Mass, amount, etc.
Reliable Measurements
 Accuracy refers to the closeness of the measure value
is to the accepted, or real, value.
 Precision refers to how close a series of
measurements are to one another.
 Error is calculated by subtracting the
experimental value from the accepted value.
 The percent error is the ratio of an error to an
accepted value.
% error = error
x 100 = accepted value – experimental value x 100
accepted value
accepted value
Example
 An experiment finds the density of lead to be 10.95
g/cm3. The literature value for the density of lead is
13.34 g/cm3.
An experiment finds the density of lead to be 10.95
g/cm3. The literature value for the density of lead is
13.34 g/cm3.
The error: accepted value – experimental
value=
 13.34 – 10.95 =
An experiment finds the density of lead to be 10.95
g/cm3. The literature value for the density of lead is
13.34 g/cm3.
The error: accepted value – experimental
value=
 13.34 – 10.95 =
2.39
The error: accepted value – experimental value=
 13.34 – 10.95 = 2.39
The % error:
error
x 100 =
accepted value
2.39 x 100 =
13.34
The error: accepted value – experimental value=
 13.34 – 10.95 = 2.39
The % error:
error
x 100 =
accepted value
2.39 x 100 = 17.9%
13.34
Practice
 Sara’s lab shows the atomic mass of aluminum to be
28.9. What is her percent error if the accepted value
is 27.0?
Practice
 Sara’s lab shows the atomic mass of aluminum to be
28.9. What is her percent error if the accepted value
is 27.0?
 27.0 – 28.9 =
Practice
 Sara’s lab shows the atomic mass of aluminum to be
28.9. What is her percent error if the accepted value
is 27.0?
 27.0 – 28.9 = -1.9
Practice
 Sara’s lab shows the atomic mass of aluminum to be
28.9. What is her percent error if the accepted value
is 27.0?
 27.0 – 28.9 = -1.9
 1.9/27.0 x 100% =
Practice
 Sara’s lab shows the atomic mass of aluminum to be
28.9. What is her percent error if the accepted value
is 27.0?
 27.0 – 28.9 = -1.9 (absolute so make it positive)
 1.9/27.0 x 100% = 7.0%
Practice
 What is the percent error in a measurement of the
boiling point of bromine if the textbook value is 60.8
&deg;C and the lab value is 40.6 &deg;C?
Practice
 What is the percent error in a measurement of the
boiling point of bromine if the textbook value is 60.8
&deg;C and the lab value is 40.6 &deg;C?
 60.8 &deg;C – 40.6 &deg;C =
Practice
 What is the percent error in a measurement of the
boiling point of bromine if the textbook value is 60.8
&deg;C and the lab value is 40.6 &deg;C?
 60.8 &deg;C – 40.6 &deg;C = 20.2 &deg;C
Practice
 What is the percent error in a measurement of the
boiling point of bromine if the textbook value is 60.8
&deg;C and the lab value is 40.6 &deg;C?
 60.8 &deg;C – 40.6 &deg;C = 20.2 &deg;C
 20.2 &deg;C / 60.8 &deg;C x 100% =
Practice
 What is the percent error in a measurement of the
boiling point of bromine if the textbook value is 60.8
&deg;C and the lab value is 40.6 &deg;C?
 60.8 &deg;C – 40.6 &deg;C = 20.2 &deg;C
 20.2 &deg;C / 60.8 &deg;C x 100% = 33.2%
Thursday Night
Birdville
Carter Riverside…
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