 # Chapter 3.2 Units of Measurement

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Chapter 3.2 Units of Measurement

Using SI Units SI = International System of Units
The standards of measurement used in science are those of the metric system All metric units are based on multiples of 10. As a result, you can convert between units easily

There are six SI base units
From these base units, all other SI units of measurement can be derived Density and pressure SI Base Units Quantity SI base unit Symbol Length meter m Mass kilogram kg Temperature kelvin K Time second s Amount of substance mole mol Volume meter cubed m3

Commonly Used Metric Prefixes
Symbol Factor kilo k 10 3 = (1000) hecto h 10 2 = (100) deca D 10 1 = (10) gram, liter, meter g, L, m deci d 10-1 = (1/10) centi c 10-2 = 1/100) milli m 10-3 = (1/1000)

Length The SI Unit for length is the meter (m)
For very large and very small lengths, a unit of length may have a prefix For small distances, the prefix millimeters (mm) could be used Prefix milli- means 1/1000, so 1 mm =0.001 m. For large distances....kilometers (km) can be used The prefix kilo- means 1000, so 1 km = 1000 m

Volume The SI unit of volume is a cubic meter (m3)
A more convenient unit of volume for everyday use is the Liter (L), a NON-SI unit A smaller, NON-SI unit of volume is the milliliter (mL) 1 mL and 1 cm3 are the same volume The units milliliter (mm) and cubic centimeter (cm3) are thus used interchangeably

Mass The SI Unit of mass is kilogram (kg)
A more convenient unit of volume for everyday use is the gram (g) There are 1000 grams in 1 kilogram (1000g = 1kg)

Weight Weight is a force that measures the pull on a given mass by gravity. The weight of an object can change with its location An astronaut weighs less on the moon but has the same mass

Density mass volume Density =
Density is the ratio of the mass of an object to its volume The relationship between an object’s mass and its volume tells you whether it will float or sink in a given situation mass volume Density = Density is an intensive property (does not depend on the amount of matter)

Units of Density The SI unit of density is kilograms per cubic meter (kg/m3) Units of density vary depending on the units for mass and volume being measured Increasing density (mass per unit volume) 10 g 0.53 g/cm3 19 cm3 10 cm3 3.7 cm3 0.88 cm3 1.0 g/cm3 2.7 g/cm3 11.4 g/cm3

Corn syrup sinks below water because it is more dense
As shown below, corn oil floats on top of water because it is less dense Corn syrup sinks below water because it is more dense Corn oil Water Corn syrup

Densities of Some Common Materials
Solids and Liquids Gases Material Density at 20°C (g/cm3) Density at 20°C (g/L) Gold 19.3 Chlorine 2.95 Mercury 13.6 Carbon dioxide 1.83 Lead 11.3 Argon 1.66 Aluminum 2.70 Oxygen 1.33 Table sugar 1.59 Air 1.20 Corn syrup 1.35–1.38 Nitrogen 1.17 Water (4°C) 1.000 Neon 0.84 Corn oil 0.922 Ammonia 0.718 Ice (0°C) 0.917 Methane 0.665 Ethanol 0.789 Helium 0.166 Gasoline 0.66–0.69 Hydrogen 0.084

Density and Temperature Relationship
The volume of most substances increases as the temperature increases, while the mass remains the same. Therefore, Density of a substance generally decreases as its temperature increases. Water is an important exception (density increases as temperature increases)

PRACTICE PROBLEM A copper penny has a mass of 3.1 g and a volume of cm3. What is the density of copper?

PRACTICE PROBLEM A rock is determined to have a mass of 8.2 g. The rock is dropped into a graduated cylinder containing 20.0 mL of water. The volume of the cylinder rises to 31.0 mL. Determine the density of the rock?

PRACTICE PROBLEM What volume would grams of Gold occupy? (Gold has a density of 19.3 g/cm3)

PRACTICE PROBLEM The density of osmium, which is the densest metal, is g/cm3. What is the mass of a block of osmium that measures 1.00 cm x 4.00 cm x 2.50 cm?

PRACTICE TIME!