Measurement and Chemistry

Measurement is central to chemistry Metric system: the set of units used for scientific measurements. SI Units: there are seven base SI units and all other units are derived from these.

Base Units of Measurement (SI UNITS: International System) Measurement Unit Name Abbreviation Mass Kilogram kg Length Meter m Time Second s Temperature Kelvin K Amount Mole mol

Length and Mass Note the SI unit for length is the meter (m) whereas the SI unit for mass is the kilogram (kg). 1 kg weighs 2.2046 lb

Mass and weight Mass is the amount of “stuff” (matter) in a material. To measure use a balance. Weight is the amount of stuff measured by gravity. On earth mass and weight are the same. To measure use a scale.

Derived Units of Measurement Volume The units for volume are given by (units of length)3. SI unit for volume is 1 m3. We usually use a non-SI unit for volume: liter or milliliter 1 mL = 1 cm3. 1 L = 1 dm3 = 1000 mL.

Other Units of Measurement (Non-SI Units) Measurement Unit Name Abbreviation Pressure atmosphere atm millimeters of mercury mm Hg pascal Pa Temperature Celsius C Energy calorie cal Joule J

Unit Conversions

A. SI Prefix Conversions 1. Find the difference between the exponents of the two prefixes. 2. Move the decimal that many places. To the left or right?

A. SI Prefix Conversions = 532 m = _______ km 0.532 NUMBER UNIT NUMBER UNIT

A. SI Prefix Conversions Symbol Factor mega- M 106 kilo- k 103 BASE UNIT --- 100 deci- d 10-1 move left move right centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12

A. SI Prefix Conversions 0.2 1) 20 cm = ______________ m 2) 0.032 L = ______________ mL 3) 45 m = ______________ nm 4) 805 dm = ______________ km 32 45,000 0.0805

B. Dimensional Analysis The “Factor-Label” Method Units, or “labels” are canceled, or “factored” out

B. Dimensional Analysis Steps: 1. Identify starting & ending units. 2. Line up conversion factors so units cancel. 3. Multiply all top numbers & divide by each bottom number. 4. Check units & answer.

B. Dimensional Analysis Lining up conversion factors: = 1 1 in = 2.54 cm 2.54 cm 2.54 cm 1 = 1 in = 2.54 cm 1 in 1 in

B. Dimensional Analysis How many milliliters are in 1.00 quart of milk? qt mL 1.00 qt 1 L 1.057 qt 1000 mL 1 L = 946 mL 

B. Dimensional Analysis You have 1.5 pounds of gold. Find its volume in cm3 if the density of gold is 19.3 g/cm3. lb cm3 1.5 lb 1 kg 2.2 lb 1000 g 1 kg 1 cm3 19.3 g = 35 cm3

B. Dimensional Analysis How many liters of water would fill a container that measures 75.0 in3? in3 L 75.0 in3 (2.54 cm)3 (1 in)3 1 L 1000 cm3 = 1.23 L

B. Dimensional Analysis 5) Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off? cm in 8.0 cm 1 in 2.54 cm = 3.2 in

B. Dimensional Analysis 6) Taft football needs 550 cm for a 1st down. How many yards is this? cm yd 550 cm 1 in 2.54 cm 1 ft 12 in 1 yd 3 ft = 6.0 yd

B. Dimensional Analysis 7) A piece of wire is 1.3 m long. How many 1.5-cm pieces can be cut from this wire? cm pieces 1.3 m 100 cm 1 m 1 piece 1.5 cm = 86 pieces