Laboratory Calculations

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Presentation transcript:

Laboratory Calculations Dimensional Analysis Percent Error Density

Dimensional Analysis Let’s define the term “Dimensional Analysis”

How to analyze dimensions Dimensional Analysis is used to convert from one unit to another. This is done by placing units in an equation or set of lines, multiplying across and dividing below to cancel out units diagonally. Ex. Convert 78 inches to feet 78 inches 1 foot 12 inches

More Examples Convert 20 pounds to ounces Convert 2.5 gallons to cups Convert 5 yards to inches

More Examples Convert 5.44 feet to meters Convert 125 mL to ounces Convert 180 days to seconds

Percent Error Accepted value: correct value for a measurement, based on lots of reliable data Experimental value: the value measured in the lab Error: The difference between the accepted value and the value you measured in the lab

Percent Error Percent % error = I accepted – experimental I accepted Example: The accepted value for the density of water is 1.00 g/mL. In the lab, you’ve measured it to be 0.75 g/mL. What is your percent error? X 100

More Examples The temperature at which water boils is 100 C. You’ve measured it at 103 C. What is your percent error? The percent yield of your experiment is 82%. If the accepted value should have been 10.0 g, what was your experimental value?

Density What does density measure? What do quantities do you need in order to calculate density? Define mass and volume. When will the density of an object change?

Examples The mass of a sample of lead is 150.00 g. The volume is 5.0 cm3. What is its density? You’ve obtained a new sample of lead that has a volume of 2.0 cm3. What is the mass of this sample?

One More Example The density of calcium is 2.8 g/cm3. If you have measured out 15.55 g, what is the volume?

Homework Complete the assigned worksheet Come up with one of each type of problem (dimensional analysis, percent error, and density). Be prepared to put your problems on the board for the class to solve tomorrow.