Units of Measurement Section 2.2

Vocabulary Measurement: dimensions, quantity, or capacity as ascertained by comparison with a standard. Quantity: something that has magnitude, size, or amount Example: the quantity represented by a teaspoon is volume, the teaspoon is a unit of measurement

Standard Measurement Nearly every measurement is a number plus a unit There has to be an agreement on measurement standards Mention distances in foot lengths

SI Measurement Le Systeme International d’Unites Adopted in 1960 Has seven base units with other units derived from these seven Are standard measurements

SI Base Units found on page 34 Quantity Unit name Unit abbreviation Length meter m Mass kilogram kg Time second s Temperature kelvin K Amount of substance mole mol Electric current ampere A Light intensity candela cd

SI Prefixes These are the most commonly used prefixes (“unit” can be grams, liters, etc): 1 unit = 100 c units 1 unit = 1 000 m units 1 unit = 1 000 000 µ units 100 units = 1 h unit 1 000 units = 1 k unit 1 000 000 units = 1 M unit

Mass and Length A measure of the quantity of matter Weight: a measure of the gravitational pull on matter Length is frequently measured in cm or km

Derived SI Units (page 36) Volume: the amount of space occupied by an object The derived SI unit of volume is m3 cm3 is often used in chemistry A non-SI unit of volume is the liter, L A smaller non-SI unit of volume is the mL 1cm3 = 1mL

Density Density: the ratio of mass to volume, or mass divided by volume D = m/V Units are expressed as kg/m3, g/L, g/mL or g/cm3 (or any other mass/volume units)

More about Density Density is a characteristic physical property It is an intensive property Can be used to help identify a substance See the table on page 38

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 The following steps will help you use conversion factors for the rest of chemistry….they don’t ever go away!

Steps for Using Conversion Factors Determine which is the smaller unit How many of the smaller units are in one of the larger units Set up the conversion factors as fractions Write what you are given, then a multiplication sign, then a fraction bar Choose a conversion factor that will make the units of the given value cancel diagonally Solve the problem.

Practice Problem Convert 42.6 cm to meters. cm is smaller, so 100 cm = 1 meter. 100 cm or ___1 m__ 1 m 100 cm 42.6 cm ● __1 m__ 100 cm This is a division problem of 42.6 divided by 100. Answer is 0.426 m

More Practice Convert: 1.843 m to km 96.3 hg to g 0.0013 Mg to mg (two step problem, go to grams first, then to mg) 4863 µL to L 1.4 x 105 g to µg