Capter 2: Units, Accuracy, Precision, Moles
Capter 2: Units, Accuracy, Precision, Moles CH 101
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This 3 page Class Notes was uploaded by Rebecca de la O on Wednesday September 7, 2016. The Class Notes belongs to CH 101 at University of Alabama - Tuscaloosa taught by Jared Allred in Fall 2016. Since its upload, it has received 26 views.
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Date Created: 09/07/16
Chapter 2: Units, Accuracy, Precision, Moles Significant Figures - All nonzero digits are significant (23 = 2 sf) - Zeroes between two non-zero digits are significant (503 = 3 sf) - Leading zeroes are not significant (0.0012 = 2 sf) - Trailing zeroes after or before a decimal point (but after a nonzero number) are significant (140.00 = 3 sf) - Trailing zeroes before an implied decimal should be avoided using scientific 3 notation (1200 1.2 x 10 = 2 sf) - In calculations, the answer should be correct to the same number as that with the fewest decimal places (12.054 x 0.53 = 6.7208 6.7) SI Units Length meter m Weight kilogram kg Time second s BASE SI UNITS Temperature Kelvin K Amount of mole Mol substance Electric ampere A Current Luminosity candela cd DERIVED SI Energy Joules J UNIT Prefixes Tera T 10 12 Giga G 109 6 Mega M 103 Kilo K 10 Milli m 10-3 Micro µ 10-6 -9 Nano n 10 Centi c 10-2 Ex. 1 km 1x 10 m 3 4 10 km 10 x 10 1 x 10 Ex. Convert speed of light to km/s 8 3.0 x 10 m/s -3 1000 m = 1 km 1 m = 10 km 3.0 x 10 x 10 = 3.0 x 10 km/s Math with Different Units Addition: 3.0000 m + 1.00 in = ? 1 inch = 2.54 cm 0.01 (m) x 2.54 = 0.0254 m 3.0000 + 0.0254 = 3.0254 m Multiplication: 15 minutes x 10 Hertz = ? 150 Hz/m 1 Hz = 1/s 150min 150 x60s -1 m xs m xs = 9000 m Be Careful with exponents!!!!!! 1 mL = 1 cm = 1 cm x 1 cm x 1 cm 1 cm = (1 x 10 m) = 10 m -6 3 Energy: A Fundamental Part of Physical & Chemical Change - Energy is the capacity to do work (comes into play when there are forces) - Work is the action of a force through a distance - Energy is a relative value defined by the state something is in Ex. Gravity pulls on things. When a ball falls and that force occurs over a distance, work is done. - Systems with high potential energy tend to change in the direction of lower potential energy, which releases energy in the surroundings - Higher potential = higher energy - Energy can enter or leave a system but it can never be created, nor destroyed - Exothermic = energy is released from a system to its surroundings - Endothermic = energy is brought into a system from its surroundings - Change in energy = final energy minus initial energy ∆E = E -E f i Ex. Start: 3 J Finish: 5 J ∆E= 5 J – 3 J = 2 J - ∆E > 0 (positive change) means energy is entering the system ∆E < 0 (negative change) means energy is leaving the system - Kinetic energy is associated with the motion of an object - Potential energy is associated with the position or composition of an object - Thermal energy is associated with the temperature of an object Moles - 1 mole = Avogadro’s number = 6.02214 x 10 of whatever you are measuring - A sample of an element with a mass that equals its atomic mass has 1 mole of that element Ex. 28Ni 58.69 amu (atomic mass unit) = 58.69 g/mol (grams per 58.69 mol) of Ni ½ mol = 0.5000 mol x 58.69 g / mol = 29.34 g - Ex. How many people equal the weight of the earth in moles? 24 Person weighs= 75 kg 22 Earth weighs = 6.0 x 10 kg 6.0x10 24 8x10 people = 23 = 0.13 mol 75 6.022x10 people/mol - Ex. How many atoms in 10 mg of Te? 10 mg 0.01000 g 1mol -5 0.01000 g Te x 127.6g = 7.837 x 10 mol 23 -5 6.022x10 atoms 19 7.837 x 10 mol x 1mol = 4.719 x 10 atoms of Te Density - Density = mass/ volume - Density is independent of the amount of the substance
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