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Chemistry 1. Metrics & measurement. Metric Units. Volume: How much space something takes up, measured in Liters or milliliters (cm3). Mass(weight): measured in grams, milligrams or kilograms. Length: measured in meters, millimeters, or centimeters. Metric Multiples.
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Chemistry 1 Metrics&measurement
Metric Units • Volume: How much space something takes up, measured in Liters or milliliters (cm3). • Mass(weight): measured in grams, milligrams or kilograms. • Length: measured in meters, millimeters, or centimeters.
Metric Multiples The great advantage of using metric units is that they are in multiples of ten. This means that you can simply move decimal points to go from one unit to another!
Metric Multiples • Kilo-K • Hecta-H • Deka-Dk • Base units= meters, Liters, grams • Deci-d • Centi-c • Milli-m
Metric Multiples km Hmdkm m dm cm mm To change metric units, simple move the decimal place along the scale from one unit to another. 25 meters becomes 2500 centimeters.
Metric Conversions • 23.5 g to mg (23,500 mg) • 435.7 ml to L (.4357 L) • .223 km to m (223m) • 22.57 cm to m (.2257 cm) • 450.3 L to ml • 45 mg to g
Density: the mass (grams) divided by the volume (milliliters): D = m/v Find D for: • A piece of cork with a volume of ml water that weighs .41 grams. (.205 g/ml) • A rock that displaces 10 ml water has a weight of 30 grams. (3 g/ml) • A chunk of ice which has a volume of 25 ml weighs 23 grams. (.91 g/ml)
Uncertainty in Measurements: because measurements always have flaws and they always involve estimation • Significant Digits – the number of certain and estimated digits in a number. • Zeroes to left of decimal point and to left of an integer do not count as significant. • All other zeroes do count as significant. • 31.76 (4 s.d.)is more accurate than 31.7 (3 s.d.) • .009210 (4 s.d.) = 9.210 x 10-3 • .0090210 (5 s.d.) = 9.0210 x 10-3
Significant digit Calculations When doing math, your answer can only have as many sigdigs as the lesser number of sigdigs: • 1.12 + 2.243 = 3.363 = 3.36 (3 sigdigs) (4 sigdigs) (4 sigdigs) (3 sigdigs) This answer can only have 3 significant digits since 1.12 only has 3 digdigs.
Base Ten Exponents • The exponents you will use in this class represent numbers which have the number of decimal places in the exponent 100 = 1; 101 = 10; 102 = 100 and so on. • Positive exponents push the decimal place to the right: 2.35 x 103 is 2,350 • Negative exponents push the decimal place to the left: 2.35 x 10-3 is .00235
Exponent Calculations • When multiplying exponential numbers, multiply the first two, then add the exponents: 1.2 x 103 x 1.2 x 103 = 1.44 x 106 • When dividing exponential numbers, divide the first two, then subtract the exponents: 1.2 x 103 / 1.2 x 103 = 1.0 x 100 =1
Exponent Calculations • To add exponents, move the decimal place to get the same exponents, then add the numbers, keeping the exponent. 1 x 102 + 1 x 103 = 1 x 102 + 10 x 102 = 11 x 102 • To subtract exponents, move the decimal place to get the same exponents, then subtract the numbers, keeping the exponent. 1 x 103 - 1 x 102 = 10 x 102 - 1 x 102 = 9 x 102
Try These! • 5.4 x 107 + 2.7 x 106 = • 2.3 x 1016 – 1.8 x 1015 = • 8.4 x 1024 / 4.2 x 1022 = • 3.2 x 103 x 2 x 1012 =
Percent Error and Yield • Percent Yield = Actual x 100 Expected • Percent Error = Actual – Expected x 100 Expected
Dimensional analysis • Used to convert units. Multiply the given by the unit you want to find on the top, and the unit you want to cancel on the bottom. • 10.5 mm = ? Meters • 10.5 mm x 1 meter= .0105 meters 1,000 mm
Measurement: • Hot or Not?
