CHEM001W - CH1 PT II MEASUREMENTS & CALCULATIONS
CHEM001W - CH1 PT II MEASUREMENTS & CALCULATIONS CHEM001W
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This 2 page Class Notes was uploaded by Catherine Notetaker on Wednesday September 28, 2016. The Class Notes belongs to CHEM001W at University of California Riverside taught by Eichler in Fall 2016. Since its upload, it has received 9 views. For similar materials see Preparation for General Chemistry in Chemistry at University of California Riverside.
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Date Created: 09/28/16
CHEM 001W Prep for General Chem 9/28/2016 CH 1 PT II Measurement & Calculations Why do we care about measurements? In order to collect data in the course of scientific inquiry, we often need to make measurements. We also need to manipulate measurements in order to interpret them. Measurements & Fundamental Units ● Distance (meters) ● Mass (grams) ● Time (seconds) ● Temperature (Celsius or K) Measurements & Derived Units ● Volume (centimeters^3 or liters) ● Density (grams/liters) ● Energy (Joule) Making a measurement & significant digits Using a graduated cylinder to make a volume measurement Read from bottom of meniscus (ex: 9.51mL → 3 significant digits “sig figs”) Significant digits in calculations and rounding (pg. 47 OpenStax) 1. Addition/Subtraction 2. Multiplication/Division 3. Multistep calculations 4. Rounding off numbers/measurements to the correct number of sigfigs Ex: Report the answer of the calculation to the correct number of sig digits: (80.21g 79.93g) / 65.22mL 80.21 79.93 = 0.28g / 65.22mL = 0.00429 g/mL Lowest number of sig digits determine where you round → = 0.0043 g/mL Numbers in Exponential Form (Scientific Notation) Expressing very large or very small numbers more easily 1. 1,700,525 g = 1.7 x 10^6 g 2. 0.000575 = 5.75 x 10^4 g Ex: 7.0 x 10^6 / 3.5 x 10^3 Divide the numbers before the exponent and subtract the exponents → = 2.0 x 10^9 Unit Conversions 1. Using the metric system to convert between SI (International System) units You must memorize the prefixes & the conversion factors for each prefix (e.g. 1kg = 1000g) Metric Prefixes: Mili = 10^3 1g = 1000mg 1mg = 0.0010g Conversions Think algebra! Ex: 100.0mg = ? g a) PROPORTIONS 100.0mg / x g = 1000mg / 1g Cross multiply & solve for x → x = 0.1000g b) 100.0mg x 1g/1000mg = 0.1000g