Lecture 4 Chapter 1-2

Lecture 4 Chapter 1-2 - General Chemistry I Fall 2007 Joann...

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General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang
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C a lc ula te d Erro rs Accuracy Absolute Error = true value - measured value % Abs. Error = (Abs. Error / true value) x 100% Precision Relative Error Standard Deviation +/- ½ Smallest Scale Division % Rel. Error = (Rel. Error/ measured value) x
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Clicker Question The density of a sample of metal was determined to be 7.76 g/cm3 +/- 0.04 g/cm3. The metal’s identity was found to be iron, d = 7.87 g/cm3. Calculate the % absolute error. (Enter the number to answer the clicker question.) Calculate the % random error.
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BIG OOPPPPS! On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mar’s atmosphere 100 km lower than planned and was destroyed by heat. 1 lb = 1 N 1 lb = 4.45 N “This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.” -a Nasa Scientist Chemistry, 8th ed. Chang Power Point Presentation
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The Metric System General Conference of Weights & Measures – SI or International System of Units 1875 Selection of Primary Standards = arbitrary. Chemistry, 8th ed. Chang
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Volume One Liter = 1000 mL (mililiters) 1000 cm 3 (cubic centimeters) 1000 cc (cubic centimeters 1 mL = 1 cm 3 = 1cc Chemistry, 8th ed. Chang
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Chemistry, 8th ed. Chang
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Given Quantity Conversion Factor New Quantity X = Dimensional Analysis # given unit # new unit # given unit new # new unit X = _________ 1. Determine which con. factor(s) are needed. 1. Carry units through calculation. 2. Use units as a “check” - proper units cancel if problem is set up correctly.
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How many mL are in 1.36 L? 1 L = 1000 mL 1.36 L x 1000 mL = 1 L 1.36 L x 1 L = 1000 mL 1360 mL The wrong way: 0.00136 L 2 mL Chemistry, 8th ed. Chang
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The speed of sound in air is about 767 mi/ hour. What is this speed in meters per second?
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Lecture 4 Chapter 1-2 - General Chemistry I Fall 2007 Joann...

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