Unit 2: Quantitative Chemistry

Measurements and Density

By the end of today’s lesson, be able to:

1.) Calculate mass, volume, and density

2.) Measure to one digit of uncertainty

Learning Target

A measurement of “compactness”: how close the atoms are to one another

Density

Calculating Density

Mass

Volume

Calculating Density

Density = Mass Volume

Units = “ grams per milliliter” (g/mL)--OR—

“grams per cubic centimeter” (g/cm3

)

Mass = measurement of the amount of matter (atoms and molecules)

Volume = the amount of space an object occupies

Calculating Density

Practice Measuring Calculate the mass of a rectangular prism

WITHOUT putting it on the balance! ◦ HINT: Make some measurements and calculate

the volume.

Color of Block Color of Tape Density (g/cm3)

Paper-white Green 0.541

Black white 0.967

Cloudy-white Orange 0.910

Clear Red 1.17

Gray Yellow 1.42

Measurements need Units!

Number

15.2

Measurement

15.2 mL

One Digit of Uncertainty

10cm, 20cm, 30cm,0cm,

Apple + Shadow Width = 14 cm

Apple + Shadow Width = 14.4 cm

10cm, 20cm, 30cm,0cm,

One Digit of Uncertainty Measure at the bottom of the meniscus

Practice Measuring Calculate the mass of a rectangular prism

WITHOUT putting it on the balance! ◦ HINT: Make some measurements and calculate

the volume.

Color of Block Color of Tape Density (g/cm3)

Paper-white Green 0.541

Black white 0.967

Cloudy-white Orange 0.910

Clear Red 1.17

Gray Yellow 1.42

Which mass was closer?

What is the percent error of your two calculations? (0% error is perfect; there is NO error)

What is the “Real” Mass?

To determine the number of sig figs and use them for rounding

To show set up for unit conversion (factor-label method)

Learning Targets

1) All nonzero numbers are significant

2) “Placeholder” zeros are not significant. Measured zeros are significant (Atlantic/Pacific Rule)

3) In scientific notation, ALL numbers written before the “x 10exp” are significant

How do we Round? …Read Aloud

1.230 x 104

Determining Significant Figures

90.210

0.0090210

90210

90210.

Calculating and Rounding

1) Multiplication/Division: Report the same number of sig figs as the value with the least.

90210 x 90.210 = 8137844.1

2) Addition/Subtraction: Report the same number of decimal places as the value with the least.

90210 + 90.210 = 90300.21

A unit equation is a simple statement of two equivalent quantities.◦ 1 km = 1000 m

◦ 1 cm = 0.01 m

◦ 100 cm = 1m

Factor Label Method

100 cm = 1 m “centi” (c)

1000 mm = 1m “milli” (m)

1 km = 1000 m “kilo” (k)

Factor Label Method

Prefixes can be applied to ANY unit, like grams or Liters

A unit conversion factor, or unit factor, is a ratio of two equivalent options.

For the unit equation 60 minutes = 1 hour, we can write two unit factors:

1 hour or 60 minutes 60 minutes 1 hour

Factor Label Method

= 1

Start with your given value in fraction form

Treat units like variables so that they will cancel.

Factor Label Method

“7.39 dollars” 7.39 dollars ____________ 1

7.39 dollars quarter ____________ x _____________ 1 dollars

7.39 dollars dollars____________ x _____________ 1 quarter

1

0.25

If you have $7.39, how much is this amount in quarters?

#1 Practice

A candy bar is approximately 220 grams. How many ounces is this?

#2 Practice

If there are 24.6 blips to every zazzle and there are 5.7 pinches to every blob and 3 blobs in a zazzle, how many blips are in 0.95 pinches?

#3 Practice

Density of an object is 4.90 g/mL what is the density of this object in pounds per Liter?

#4 Practice

A cube is measured to have a volume of 13,506m3, what is this volume in km3 ?

#5 Practice