Unit 2 Basic Chem
Unit 2 Basic Chem chm 2023
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This 3 page Class Notes was uploaded by Alicia Doan on Monday August 29, 2016. The Class Notes belongs to chm 2023 at University of South Florida taught by Dr. Daniel Cruz-Ramírez de Arellano in Summer 2015. Since its upload, it has received 4 views. For similar materials see Chemistry for Today in Chemistry at University of South Florida.
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Date Created: 08/29/16
Unit 2: Chemistry and Measurement 2.1 Units of Measurement Everyone in the world, except for the United States -.- use the International System of Units (SI) In chem both metric and SI is used: Measurements Metric SI Length Meters (m) Meters (m) Volume Liters (L) Cubic meter (m ) Mass Gram (g) Kilogram (kg) Temperature Degree Celsius (°C) Kelvin (K) Time Second (s) Second (s) Length : 1m = 100cm 1m = 39.37 in 1m = 1.094 yd 2.54 cm = 1 in Volume : 1m = 1000L 1L = 1000mL 1mL = 1 cm 3 1L = 1.057qt 946.4 mL = 1qt Mass : 1 kg = 1000 g 1 kg = 2.205 lb 453.6 g = 1 lb Temp : Water freezes at 0 °C & in Fahrenheit (°F) 32° Water boils at 100 °C & in Fahrenheit (°F) 212° In the SI unit, the temp is measure in Kelvin (K), and the lowest temp is 0 K. Time : 1 day = 24 hrs 1 hr = 60 mins 1 min = 60 s 2.2 Measured numbers and significant figures Signif Figs are all the digits including the estimate digits. However, a zero may or may not be signif depending on its position in the number EX: 4.5 g = 2 sigfig 120.08 m = 5 sigfig 8500,000 mL = 2 sigfig 0.00004 = 1 sf 25.0 °C = 3 sf 16 .00 = 4 sf 2.3 Significant Figures in Calculations In multiplication/division the final answer is written so that it has the same number of sf as the measurement with the fewest decimal places In addition/substraction, the final answer is written so that it has the same num of decimal places as the measurement with the fewest decimal places In science you round off long numbers to 4 sf or less. Round up when the last digit is 5 or higher and round down when the digit is 4 or less EX: 4.79310 = 4.80 22.328 = 22.33 or 22.3 When multiplying or dividing with sf, the answer will also be in sf, the sf of your answer should be the same amt of digits as the smallest sf digit in of the equation EX : 56.8 (three sf) x 0.37 (two sf) = 21.016 = 21 (two sf, aka the smallest sf in this eq) 2.4 Prefixes and Equalities A prefix placed in front of a metric or SI unit changes the size of the unit by factors of 10 An equality of shows the relationship btw 2 units that measure the same quantity of length, volume, mass, or time EX: 1 kilometer (1 km) = 1000 meters (1000m = 10 m) 3 3 1 kiloliter (1 kL) = 1000 liters (1000L = 10 L)3 1 kilogram (1 kg) = 1000 grams (1000g = 10 g) 2.5 Writing Conversion Factors Conversion factors are used to express a relationship in the form of a fraction 2 conversion factors can be written for any relationship in the metric or US system A % is written for a conversion factor by expressing matching units as the pasrt in 100 parts of a whole Small ratios are expressed as parts per million (ppm) and parts per billion (ppb) 2.6 Problem Solving Using Unit Conversion Conversion factors are useful when changing a quantity expressed in 1 unit to a quantity expressed in another unit In the problem solving process, a given unit is multiplied by 1 or more conversion factors that cancel units until the needed answer is obtained 2.7 Density Density = massof substance÷volumeof substance The density of a sub is usually g/mL or g/cm 3 Specific gravity (sp gr) compares the density of a sub to the density of water, 1.00g/mL To obtain vol of a sub, you take the initial measurement of a beaker of water, then place the sub/item in the beaker, note the vol of the beaker after places the object in, find the diff in vol which will be the vol of the object/sub.
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