Section 2-2 Units of Measurement CH. 2 - MEASUREMENT Section 2-2 Units of Measurement

A. Number vs. Quantity UNITS MATTER!! Quantity – is something that has magnitude, size, or amount; number + unit UNITS MATTER!!

B. SI Units SI units of measurement is the system that all scientists around the world have agreed upon as the single measurement system. SI units are defined in terms of standards of measurement. The standards are objects or natural phenomena that are of constant value, easy to preserve and reproduce, and practical in size.

C. SI Base Units Quantity Symbol Base Unit Abbrev. Length l meter m Mass m kilogram kg Time t second s Temp T kelvin K Amount n mole mol

D. SI Prefixes – pg 35 Prefix Symbol Factor mega- M 106 kilo- k 103 BASE UNIT --- 100 deci- d 10-1 centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12

E. SI Prefix Conversions A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other. 1. Find the difference between the exponents of the two prefixes. 2. Move the decimal that many places. To the left or right?

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

E. SI Prefix Conversions Large unit being converted to a smaller unit: Move the decimal place to the right the specified number of places Small unit being converted to a larger unit: Move the decimal place to the left the specified number of places

E. 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

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

E. SI Prefix Conversions 2.1 1) 2100 g = ______________ kg 2) 5.5 L = ______________ mL 3) 45 km = ______________ m 4) 85 m = ______________ mm 5,500 45,000 85,000

M V D = F. Derived Units 1 cm3 = 1 mL 1 dm3 = 1 L Combination of base units. Volume (m3 or cm3) – the amount of space occupied by an object length  length  length 1 cm3 = 1 mL 1 dm3 = 1 L D = M V Density (kg/m3 or g/cm3) – the ratio of mass to volume mass per volume

G. Density Mass (g) Volume (cm3) Density is a characteristic physical property of a substance and does not depend on the size of the sample; the ratio of mass to volume is constant. Mass (g) Volume (cm3)

G. Density Density is dependent on temperature. An increase in temperature usually causes a decrease in density for most substances.

H. Problem-Solving Steps 1. Analyze 2. Plan 3. Compute 4. Evaluate

I. Solving Density Problems An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass. GIVEN: V = 825 cm3 D = 13.6 g/cm3 M = ? WORK: M = DV M = (13.6 g/cm3)(825cm3) M = 11,200 g

I. Solving Density Problems A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid? GIVEN: D = 0.87 g/mL V = ? M = 25 g WORK: V = M D V = 25 g 0.87 g/mL V = 29 mL

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

J. 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.

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

J. Dimensional Analysis How many milliliters are in 1.00 quart of milk? (Hint: 1.057 qt = 1 L) qt mL 1.00 qt 1 L 1.057 qt 1000 mL 1 L = 946 mL