1. Topic: Math Topics Aim: How do you calculate density & percent error?
Do now: How many Liters are in 7543mL?
HW: I NEED LAB CONTRACTS!!

2. Density the ratio of a mass of an object to its volume
Density of a substance is constant, regardless of the size of sample
Density can be used to ID an unknown
Density units – g/mL or g/cm3
Mass – g
Volume – mL or cm3
- Density = Mass / Volume (D = M / V)

3. June 2009 Regents, #16
A large sample of solid calcium sulfate is crushed into smaller pieces for testing. Which two physical properties are the same for both the large sample and one of the smaller pieces?
(1) mass and density
(2) mass and volume
(3) solubility and density
(4) solubility and volume

4. Examples
The mass of an object is 900g and its volume is 30cm3. What is its density?
The density of CCl4 is 1.58g/mL. What is the mass of 95.7mL of CCl4?
A substance is known to have a density of 2.43g/cm3. A sample of this substance has a mass of 9.46g. What should the volume of this substance be?
During a laboratory experiment, a sample of zinc was found to have a mass of g and a volume of 8.9 mL. What is the density, expressed to the correct number of significant figures?

5. Example
In the opening scenes of the movie Raiders of the Lost Ark, Indiana Jones tries to remove a gold idol from a boob—trapped pedestal. He replaces the idol with a bag of sand of approximately equal volume. (Dgold = g/cm3, Dsand = 2 g/cm3)
Did he have a reasonable chance of not activating the mass-sensitive booby trap?
In a later scene, he and a guide play catch with the idol. Assume that the volume of the idol is about 1.0L. If it were solid gold, what mass would the idol have? Is playing catch with it plausible?

6. Calculating Percent Error
compares what a student calculated, found, or measured in the lab (called the measured value) with what the accepted value is, (i.e. in a perfect world with no flaws, the value that would be gotten)
Reference Table T
(measured value – actual value)/actual value x 100

7. Examples
A student calculated the % by mass of water in BaCl2 ∙ 2H2O to be 16.4%, but the accepted value is 14.8%. What is the student’s % error?
A student determined the percentage of water of hydration in BaCl2 ∙ 2H2O by using the data in the table below. Quantity Measured Value Obtained
mass of grams
BaCl2 ∙ 2H2O
mass of BaCl grams
% of water calculated %
The accepted percentage value for the water of hydration is 14.75%. What’s the student’s % error?