Review: Standard Units of MeasurementMs FedorArts and College Preparatory Academy

ChemCatalyst1. How many centimeters (cm)

are in a meter (m)? 2. Convert 15 grams (g) into

kilograms (kg)

Upcoming Events1. September 20th: Lab practical

◦ Know lab equipment◦ Know how to read volume of a

graduated cylinder◦ How to read/mass something on a

balance◦ Give precise measurements

2. September 24th: Section 1 Quiz ◦ Review sheet covering content on

lab safety, equipment, matter, measurement

Activity: Metric MeasurementGoal: review units of measurement1. Work with lab mates to

measure the height of your desk

2. Write your measurement on the overhead

3. Find the average height of the desk

SI Units (Systeme International d’ Unites)

Units need to be the same in order to be comparable.

Science uses metric units, which has a base of 10, making converting units very easy.

Prefixes are used to differentiate between units.

Metric Prefixes You Should Know

exampleKilogramKilo- = thousand“thousand grams”

CentimeterCenti- = one hundreth“one hundreth meter”

ChemCatalyst

What do these numbers have in common?2/2 6/6 11 x 100

They are all equal to one.

Converting UnitsUnits can be converted using a conversion factor:

Conversion factor: relationship between the units

Ex: 1000 grams (numerator) per kilogram (denominator)

1000g 1 kg

Think of this line as meaning “per”

Conversion UnitsBecause 1000 g = 1 kg,

1000g = 1 kg = 1 1 kg 1000g

This means that we can multiply any number by it, and the value will not change, because we are basically multiplying by one.

ExampleLet’s say that we have to measure out 5 liters of a solution, but our graduated cylinder is divided into milliliters (mL).

We need to know how many milliliters we need.

What is the relationship between liters and milliliters? There are 1000mL in 1L

When using a conversion factor:Always multiply across first (do not cross-multiply!!!)

Cancel the units that are on both the top and bottom that are the same

5 L x 1000 mL = 5000 L mL = 5000 mL

1L 1 LUnknown unit (unit we’re converting to)

known unit (unit we’re converting from) We always put the unknown unit on the top (numerator), and the known unit on the bottom (denominator)

Practice QuestionHow many centimeters (cm) are in 6 meters (m)?

6 m x 100 cm = 600 m cm = 600 cm

1 m 1 m

What would be the conversion?

?

Practice: 1. Convert 30 grams into centigrams

◦ 30 g x 100 cg = 3000 g cg = 3000 cg

1 g 1 g2. Convert 20 cm into m

◦ 20 cm x 1 m = 20 cm m = 0.20 m 100 cm 100 cm3. Convert 2 Liters into milliliters

◦ 2L x 1000 mL = 2000 L mL = 2000 mL 1L 1 L

Assignment: Converting Units practice

Do the practice problemsUse the conversion factor

method for the first section, then try your own method for the second section