UNITS OF MEASUREMENTChapter 2 : Section 2

Objectives Distinguish between a quantity, a

unit, and a measurement standard Name SI units for length, mass, time,

volume, and density Distinguish between mass and

weight Perform density calculations Transform a statement of equality to

a conversion factor

Units of measurement Quantity – magnitude, size, or

amount 5 2,000,000

0.030o Units – compare what is measured

with defined size mL g feet

Quantity has no meaning without the unit 5 mL 100 g 2,000,000

feet

SI Measurement Le Systeme International d’Unites

Adopted 1960 as world-wide agreed upon standards

Base

unit

s

Some SI Base Units Mass – measure of the amount of

matter in an object Grams (g) Electronic scale or triple beam balance

Volume – amount of space an object takes up Liters L V = L X W X H (cm3)

Graduated cylinder Water displacement

Weight – measure of the gravitational pull on matter Example : Moon has 1/6 weight

Visual Concept 1 – Click Here

Visual Concept 2 – Click Here

Metric Prefixes Tera- T 1012 1 000 000 000 000 Giga- G 109 1 000 000 000 Mega- M 106 1 000 000 kilo- k 103 1000 hecto- h 102 100 deka- da 10 10 - - - - deci- d 10-1 0.1 centi- c 10-2 0.01 milli- m 10-3 0.001 micro- u (mu) 10-6 0.000 001 nano- n 10-9 0.000 000 001 pico- p 10-12 0.000 000 000 001

Derived SI units

Combination of SI base units Examples

Area m2 L x W Volume m3 L x W

x H Density Kg/m2

mass/volume Molar mass Kg/mol

mass/moleSpeed : 2 measurements

distance divided by

time

Volume and Density Volume = Length x Width x Height

1 cm x 1 cm x 1 cm = 1 cm3

Density = mass / Volume

Sample Problem 2-1

A sample of aluminum metal has a mass of 8.4 g. The volume of the sample is 3.1 cm3. Calculate the density of aluminum.

Write density equation

Step 1:D

V=

m

List your variables

Step 2:D

V

m

=

=

= ?

8.4 g

3.1 cm3

Replace variables in the equation

Step 3:

8.4 g

3.1 cm3

=

Rearrange the equation

Step 4:

SolveStep 5:

2.7 g/cm3=

Rearranging EquationsD

V=

m

Multiply both sides by V

Step 1:

Solve for m:D

V=

m

DV

=m

V Vx x

V’s will cancel out leaving m by itself and on top

Step 2:so: D=m Vx

Solve for V:

Rewrite the equation

Step 3:

Multiply both sides by V

Step 1:

Divide both side by D

Step 2:D

V=

mV Vx x

D = mV xDD

DV =

m

so:

Rewrite the equation

Step 3:

Practice pg.40 #1-31. What is the density of a block of marble that

occupies 310. cm3 and has a mass of 853 g?

2. Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of 0.351 cm3?

3. What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/mL?

1.14 g

2.75 g/cm3

5.60 mL

Density of Some Common Substances Substance Density (g/cm3)

Air 0.0013 Feathers 0.0025 Wood(Oak) 0.6 - 0.9 Ice  0.92  Water  1.00 Bricks  1.84 Aluminum  2.70 Steel  7.80 Silver  10.50 Gold  19.30 

Conversion Factors Ratio derived from the equality between

two different units that can be used to convert from one unit to the other

Equalities 1 dollar = 4 quarters 1 kg = 1000 g 1 Km = 0.6213 miles

1 dollar 4 quarters4 quarter or 1 dollar

Visual Concept – Click Here

=So: How many quarter are there in $55 ?

55 dollars

x1 dollars

4 quarters = 220

quarters

Making conversions How many miles are in 15 Km?1. Write given value:2. Choose conversion factor3. Multiply top and divide bottom

11.0 miles

x0.6213 miles

1 km = 17.7

km

Video Concept – Click Here

Sample Problem 2.2Express a mass of 5.712 grams in milligrams and in kilograms.

5.172 g

x1 g

1000 mg = 5172

mg

5.172 g x1000 g

1 kg = 0.005172

kg

Practice 1 & 2 pg. 421. Express a length of 16.45 m in

centimeters and in kilometers.

2. Express a mass of 0.014 mg in grams.

1. 1645 cm, 0.01645 km2. 0.000 014 g

Answers: