Bell-ringer You are driving in your car down the interstate (70 mph) to Tuscaloosa to watch the University of Alabama crush the Tennessee Volunteers. It appears as though you are going to be late for the kickoff if you don’t speed up. If you are traveling at a speed of 90 km/h, are you breaking the speed limit? You are driving in your car down the interstate (70 mph) to Tuscaloosa to watch the University of Alabama crush the Tennessee Volunteers. It appears as though you are going to be late for the kickoff if you don’t speed up. If you are traveling at a speed of 90 km/h, are you breaking the speed limit?

Chapter 2, Section 2: Units of Measurement Coach Kelsoe Chemistry p. 33–42

Units of Measurement Measurements are quantitative. Measurements are quantitative. We must use units to make any kind of measure. We must use units to make any kind of measure. –Imagine getting a treasure map saying, go 5 right, 10 forward, and left 7 to find Captain Jack Sparrow’s treasure. How far would you have to go? Measurements represent quantities. A quantity is something that has magnitude, size, or amount. Measurements represent quantities. A quantity is something that has magnitude, size, or amount.

Units of Measurement Nearly every measurement we make involves a number and a unit. Nearly every measurement we make involves a number and a unit. Many measurements we use have different units, like feet or meters for distance, or gallons or liters for volume. Many measurements we use have different units, like feet or meters for distance, or gallons or liters for volume.

SI Measurement Scientists all over the world have agreed on the SI system of measurement. This system was adopted in Scientists all over the world have agreed on the SI system of measurement. This system was adopted in –SI stands for Le Système International d’Unités SI has seven base units, and most other units are derived from these seven. SI has seven base units, and most other units are derived from these seven. Some non-SI units are still commonly used. Some non-SI units are still commonly used. SI units are defined according to standards of measurement. SI units are defined according to standards of measurement.

SI Base Units There are 7 base units in the SI system: There are 7 base units in the SI system: –Meter (m)- length (l) –Kilogram (kg)- mass (m) –Second (s)- time (t) –Kelvin (K)- temperature (T) –Mole (mol)- amount of substance (n) –Ampere (A)- electric current (I) –Candela (cd)- luminous intensity (I v )

SI Prefixes Prefixes can be added to a base unit to represent quantities larger or smaller than the base unit. Some examples of prefixes: Prefixes can be added to a base unit to represent quantities larger or smaller than the base unit. Some examples of prefixes: Giga- (G)10 9 Mega- (M)10 6 Kilo- (k)10 3 Hecto- (h)10 2 Deka- (da)10 1 Deci- (d)10 -1 Centi- (c)10 -2 Milli- (m)10 -3 Micro- (µ)10 -6 Nano- (n)10 -9

Mass The SI unit for mass is the kilogram (kg). The SI unit for mass is the kilogram (kg). When we measure smaller objects, especially in the lab, we will use grams rather than kilograms. When we measure smaller objects, especially in the lab, we will use grams rather than kilograms. Mass and weight are different! Mass and weight are different! –Mass is the amount of matter in an object. –Weight is the gravitational pull on matter. Which measure can change without affecting the substance measured? Which measure can change without affecting the substance measured?

Bell-ringer Convert the following quantities: Convert the following quantities: –525 mL to liters –7 km to centimeters –0.003 Gs to seconds –48 g to micrograms

Length The SI unit for length is the meter. The SI unit for length is the meter. To express longer distances, we use the kilometer. To express longer distances, we use the kilometer. Most countries use the kilometer when measuring distances, but we use miles. Most countries use the kilometer when measuring distances, but we use miles. The centimeter is used for shorter distances. The centimeter is used for shorter distances.

Derived SI Units Many SI units are combinations of the standard SI units. Many SI units are combinations of the standard SI units. Derived units usually come from multiplying or dividing two standard SI units. Derived units usually come from multiplying or dividing two standard SI units. Some combination units are given their own names, like the Pascal. Some combination units are given their own names, like the Pascal. We can also add prefixes to derived units. We can also add prefixes to derived units.

Derived Units QuantitySymbolUnitAbbrev.Derivation AreaA Square meter m2m2m2m2 Length x width VolumeV Cubic meter m3m3m3m3 Length x width x height DensityD Kilograms per cubic meter kg/m 3 Mass/Volume Molar Mass M Kilograms per mole kg/mol Mass/ amount of substance Concentrationc Moles per liter M Amount of substance/ vol. Molar volume VmVmVmVm Cubic meters per mole m 3 /mol Vol./amount of substance EnergyEJouleJ Force x length

Volume Volume is the amount of space occupied by an object. It is found by multiplying length x width x height. Volume is the amount of space occupied by an object. It is found by multiplying length x width x height. The standard unit for volumes of solids is m 3. For liquids and gases it is liters (L). The standard unit for volumes of solids is m 3. For liquids and gases it is liters (L). What if we’re comparing volumes of solids to liquids or gases? What if we’re comparing volumes of solids to liquids or gases? –One liter (1 L) is equal to 1000 cm 3. –One milliliter (1 mL) is equal to 1 cm 3. –Also keep in mind that cm 3 = cc.

Converting Volumes If 1 meter is equal to 100 centimeters, then wouldn’t 1 m 3 be equal to 100 cm 3 ? If 1 meter is equal to 100 centimeters, then wouldn’t 1 m 3 be equal to 100 cm 3 ? NO!!!!!!!! Here’s why: NO!!!!!!!! Here’s why: –1 meter x 1 meter x 1 meter = 1 m 3. –If we measured the same object in cm then: –100 cm x 100 cm x 100 cm = cm 3 –So we see that 1 m 3 does NOT equal 100 cm 3 ! Remember that mL and cm 3 are interchangeable! Remember that mL and cm 3 are interchangeable!

Density Density is the ratio of mass to volume. Density is the ratio of mass to volume. Mathematically, we see it like this: Mathematically, we see it like this: –Density = mass/volume or D = m/V It may be easier to see it like this: It may be easier to see it like this: m DV

Density The standard unit for density is kg/m 3, but in the lab, this unit is typically way too large. We may use units like g/cm 3 or g/L. The standard unit for density is kg/m 3, but in the lab, this unit is typically way too large. We may use units like g/cm 3 or g/L. Density is a characteristic physical property. It is an intensive property because it doesn’t matter how much we have, the measurement will always be the same. Density is a characteristic physical property. It is an intensive property because it doesn’t matter how much we have, the measurement will always be the same. Different densities is what allows things to float or sink in water. PURE water has a density of 1 g/mL. Different densities is what allows things to float or sink in water. PURE water has a density of 1 g/mL. –If a substance is less dense than water, it floats. –If it is more dense than water, it sinks.

Conversion Factors 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. 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. Conversion factors are arranged to cancel out the original unit. Conversion factors are arranged to cancel out the original unit. For example, converting 78 feet to yards: For example, converting 78 feet to yards: –78 feet x 1 yard = –26 yards 3 feet

What if… What if I had chosen the wrong conversion factor? Then… What if I had chosen the wrong conversion factor? Then… –78 feet x 3 feet = 234 ft 2 /yard Even though 3 feet/1 yard is a correct conversion factor, it does not give us the units we need! Even though 3 feet/1 yard is a correct conversion factor, it does not give us the units we need! 1 yard

Using Multiple Conversion Factors What if I asked you to convert inches to miles? What if I asked you to convert inches to miles? You would have to do the following: You would have to do the following: – inches x 1 foot x 1 mile = 1.75 miles 12 inches 5280 feet