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Topic: Math & Lab Skills

Topic: Math & Lab Skills. Aim: How do you calculate density & percent error? Do now : How many Liters are in 7543mL? HW: I NEED SIGNATURE FORMS AND LAB CONTRACTS!!. Density. the ratio of a mass of an object to its volume

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Topic: Math & Lab Skills

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  1. Topic: Math & Lab Skills Aim: How do you calculate density & percent error? Do now: How many Liters are in 7543mL? HW: I NEED SIGNATURE FORMS AND 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 63.20 g and a volume of 8.9 mL. What is the density, expressed to the correct number of significant figures?

  5. 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

  6. 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 MeasuredValue Obtained • mass of 3.80 grams • BaCl2∙ 2H2O • mass of BaCl2 3.20 grams • % of water calculated 15.79% • The accepted percentage value for the water of hydration is 14.75%. What’s the student’s % error?

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