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 axisBest 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

X-Axis- independent variable- change on purpose

Y-Axis- dependent variable- changes in response

Constant- all other variables do not change

Control- standard used for comparison

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.

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

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: 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 = -1.91.9/27.0 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 °C and the lab value is 40.6 °C?

Practice

What is the percent error in a measurement of the boiling point of bromine if the textbook value is 60.8 °C and the lab value is 40.6 °C?

60.8 °C – 40.6 °C =

Practice

What is the percent error in a measurement of the boiling point of bromine if the textbook value is 60.8 °C and the lab value is 40.6 °C?

60.8 °C – 40.6 °C = 20.2 °C

Practice

What is the percent error in a measurement of the boiling point of bromine if the textbook value is 60.8 °C and the lab value is 40.6 °C?

60.8 °C – 40.6 °C = 20.2 °C20.2 °C / 60.8 °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 °C and the lab value is 40.6 °C?

60.8 °C – 40.6 °C = 20.2 °C20.2 °C / 60.8 °C x 100% = 33.2%

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