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WVU CHEM 115 - Lecture 2(1)

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Review Temperature Conversion from Last Lecture Convert 822°F to Kelvin. A Prerequisite for Chem 115 is one of the following: 1. Passing grade (C or better) in Chem 110B at WVU. 2. Score of 600 or better on SAT/Math or score of 26 or better on ACT/Math. 3. Minimum composite score of 24 on the two parts of the QRA (math placement exam). 4. Transfer credit for Chem 110, 111, 112, or 115 from another institution. See me as soon as possible if this is your prerequisite. Proof of transfer credit (from Admissions and Records) must be shown. Include information about your prerequisite on the white card. Such as: a. Chem 110, 111, or 112 grade, instructor, and semester b. Date and score of chemistry placement exam. c. ACT/Math or SAT/Math score. d. Transfer information Any student without the proper prerequisite will be dropped from the roster!! 712kHomework for Chem 115: 1. Read syllabus. 2. Chem 115 students need to purchase either the all digital package OR the Chem 115 package with access to Connect (so not both!). Both packages should contain access codes for the Connect and ALEKS online homework systems and both should have the Chemistry by Silberberg, 6th ed. textbook. The all digital package provides the textbook in electronic form only whereas the regular Chem 115 package provides the textbook in print form. 3. Purchase Chem 115 laboratory manual, goggles, and apron from the bookstore. (White aprons from Book Exchange are not permitted.) Bring manual, apron, and goggles to first lab (Tuesday, August 26th). 4. Go to website for online homework: www.aleks.com. Register and begin working on the assessment. Significant Figures Significant Figures: digits used to represent a measured number such that only the digit farthest to the right is uncertain. The digit farthest to the right has some error in its value but is still significant. NOTE: Sig. figs. give information on error. As # sig. figs. increases, error decreases, and measuring device precision increases. Example. Measure the mass of lump of Fe on different balances. Triple Beam Balance = 1.6 g (±0.1 g) (marked at every 1 g) Electronic Balance = 1.597 g (±0.001 g) Which measurement has less error?Rules for Counting Significant Figures 1. Find the first nonzero digit. This first digit and all digits to right of this digit are significant if written. # SF # SF Ex. 24.5 cm 1.003 J 311.2 in 0.003 g 27 ft 0.0102 cal 24.505 s 0.00050 kg 5 qt 5 pencils 2. Measured numbers greater than one that end in zero(s) are ambiguous in sig. figs. and MUST be written in standard exponential form. # SF # SF Ex. 1200 ft 1.200x103 ft 1.2x103 ft 1200. ft 1.20x103 ft 1200.0 ft Standard Exponential Form (Scientific Notation) # x 10n * Add one to exponent of 10 each time move decimal to left. * Subtract one from exponent of 10 each time move decimal to right. 14,000 0.000065 7500 0.0005 1380 0.0100 120.0x10-3 0.00071x103Rounding Rules: 1. If the first digit to be dropped is 4 or less, then it and all the following digits are dropped from the number. 2. If the first digit to be dropped is 5 or greater, then the last retained digit of the number is increased by 1. Example: Round each of the following numbers to 2 sf. 0.871 0.8750 0.878 0.865 0.9751 14,263 0.9959 599,862,125 Multiplication and Division of Measured Numbers Rule: The measured number with least # sig. figs. limits the sig. figs. on the answer. Examples: A. (6.4 x 3.159)/23.3 = ? B. (1285.5)/257.1 = ? C. 11.7 x 110.99 = ?Addition and Subtraction of Measured Numbers Rule: The measured number with least # decimals limits the # decimals on the answer. Examples: C. (6.21x10-7)+(6.2x10-8)=? A. 5.195 23.42 + 130.2 B. 8.99 + 2.1 Sig Figs: Mixed Operations A. 129.7/(129.7 + 0.75) = ? B. (301.7 – 32.00) = ? 1.8000Factor-Label Method (aka Dimensional Analysis) • To change units on a measured value, multiply the number by a conversion factor. The conversion factor is obtained from a conversion relationship. The conversion factor always has the new units on top and the old units on the bottom (to cancel the old units). • Examples of conversion relationships: • 12 in = 1 ft, 1 in = 2.54 cm, 1 kg = 103 g Factor-Label Method: Example Convert 343 in to yd. (Use 1 in = 2.54 cm and 0.9144 m = 1 yd) The gravity on Saturn is 1117.0 cm/s2. What is the gravity in units of yd/min2? 9.53ydMetric System Conversions 1. 7.591 mL = ? L 2. 311 ks = ? μs 3. 8.501x10-2 cg = ? kg Density • d = mass/volume Units: g/mL, g/cm3, kg/m3 (SI), g/L • Value does NOT depend on size of sample. • Value of density depends on: – Substance – Physical state – Temperature (as T increases, d decreases) Substance density (g/mL) Liquid water 1.000 at 4 °C Ice 0.917 Fat 0.94 Hg(l) 13.55Problem Solving with Density A. Determine the density (g/mL) for a 5.00 mL urine sample from a patient suffering from diabetes that has a mass of 5.025 g. B. Density as a Conversion Factor How many liters of gasoline contain 2.2 kg of gasoline (density of gasoline is 0.66 g/mL) Continued… C. A graduated cylinder contains 28.0 mL of water. What is the new water level after 35.6 g of silver metal is submerged in the water? (Density of silver is 10.5 g/mL)Weight/Mass Percent and Use of as Conversion Mass Percent Mass % = mass component x 100% mass whole Example: A solution is made by dissolving 10.5 g sugar in 80.5 g water. Calculate the mass percentages of sugar and water in the solution. Mass Percent as Conversion Factor Examples: A sample of coal is 4.7% sulfur (w/w). How many pounds of sulfur are present in 2.5 tons of this coal? A sample of environmental grade HCl solution has a density of 1.19 g/mL and is 37.5% HCl. What volume of his solution will provide 20.0 g


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