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  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 g/cm 3. The literature value for the density of lead is g/cm 3.

The error: accepted value – experimental value= – = An experiment finds the density of lead to be g/cm 3. The literature value for the density of lead is g/cm 3.

The error: accepted value – experimental value= – = 2.39 An experiment finds the density of lead to be g/cm 3. The literature value for the density of lead is g/cm 3.

The error: accepted value – experimental value= – = 2.39 The % error: error x 100 = accepted value 2.39 x 100 = 13.34

The error: accepted value – experimental value= – = 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 What is her percent error if the accepted value is 27.0?

Practice Sara’s lab shows the atomic mass of aluminum to be 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 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 What is her percent error if the accepted value is 27.0? 27.0 – 28.9 = /27.0 x 100% =

Practice Sara’s lab shows the atomic mass of aluminum to be 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 °C 20.2 °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 °C 20.2 °C / 60.8 °C x 100% = 33.2%

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