Measurements The “inch-pounds” or customary unit measurement system has been used in the US for as long as we can remember. We, the US, are one of the only countries that has no fully adopted the SI, International

System of Units, or metric unit measurements. Many believe that the metric system is a much easier system to use. The SI system is what is

ALWAYS used in chemistry (all sciences) because it allows of universal communication.

Measurements

• We use measurements in everyday life and in science

• A measurement includes both a value and a unit • Measurements represent quantities – a quantity is something that

has magnitude, size, or amount.

• There are both qualitative measurements and quantitative measurements • It takes a long time to walk home from school

• It took me 2 hours and 14 minutes to walk home from school

Common Measurements

• Mass • The quantity of matter an

object contains • SI Unit for Mass is kg

• Weight • force – measure of pull on

the mass of an object due to gravity

• We not really talk about the “weight” of objects in chemistry!

• Length • SI Unit for length is m

• Volume • the space occupied by a

sample of matter • volume changes when

temperature changes • V = l x w x h • SI Unit for volume is L • 1L = 1dm3 • 1mL = 1 cm3 = 20 drops

Common SI Information

• 1 milliliter is the same volume as 1 cm3

• 1 milliliter of water has a mass of 1 g

• 1 liter of water has a mass of 1 kg

• 1 penny is exactly 2.5 grams

• 1 nickel is exactly 5 grams

• A doorknob is about 1 meter from the ground

Density • Different types of matter have different

densities: • More mass in a smaller volume = more

dense • Less mas in a greater volume = less dense • More dense solid - sinks in its own liquid • Less dense solid – floats in its own liquid

• Density is the mass of an object in a given space • Typically density will

decrease if the volume and temperature of an object increase and visa-versa.

• NOT TRUE for water!

• Density = mass ÷ volume

• Units: g/ml or g/cm3

Calculations & Conversions

• Conversion Factor – any fraction or ratio in which the numerator equals the denominator. When two numbers are equal their ratio will be one. • 1 foot = 12 inches is the same as writing 1 foot/12 inches or

12 inches/1 foot • 3200 g x (conversion factor 1 kg/1000g) = 32Kg

• Dimensional Analysis – using the conversion factor to change on unit into another unit. • Convert 36 inches into feet.

36 inches x 1 foot = 3 feet 1 12 inches

SI Prefixes The prefixes is connected to the measurement to express very large or very small numbers. Where the - - is can have any of the base units of gram (mass), meter (length), or liter (volume)

Metric Mania Wkst Work independently or at your table group to complete the front

side!

SI Units and Variables for various measurements

Measurement Variable SI Unit Symbol Other Units Symbols

Length l Meter m

Mass m kilogram kg

Time t second s Hour, minute hr, min

Temperature T Kelvin K Celsius °C

Amount/count

n mole mol

Volume v Cubic meter

cm3 Liter L = dm3

Energy E Joule J Calorie cal

Pressure P Pascal Pa Kilopascal

Atmosphere kPa atm

Density D grams/cu

bic centimeter

g/cm3 Grams/milli

meter g/ml

Dimensional Analysis

• Multiple Step Problems – more than 1 conversion factor • Given (con. factor) (con. factor)(con. factor) = want

• Convert 15 days into minutes

15 days x 24 hours x 60 mins = 21,600 mins 1 1 day 1 hour

• How many hours are in a year? hrs_ year

Try this one!

• If you are going 50 miles per hour, how many feet per second are you traveling?

Hint: 5280 feet / 1 mile