Chemistry 103Lecture 3

Outline

I. Mathematics of Chemistry– Dimensional Analysis– Density– Temperature Scales

II. Matter Classified

Math Operations

• Calculate each to the correct number of sig figs.

• 32.145 cm x 17.8 cm x 25 cm =

• 1450.0 kg + 250 kg + 1.235 kg =

Dimensional Analysis

Review

Dimensional Analysis

• A problem solving method in which the units (associated with numbers) are used as a guide in setting up the calculations.

unitsdesiredinAnswerunitgiven

unitdesiredxunitgivenintMeasuremen

Conversion Factor

Dimensional Analysis

How many seconds are in 2 minutes?

2 minutes x 60 seconds =

1 minute

120 seconds (exactly)

Learning Check

• If a bucket contains 4.65L of water. How many gallons of water is this?

(1 gallon = 4qts, 1L = 1.057qt)

A. 1.23 gallons

B. 4.92 gallons

C. 17.6 gallons

Dimensional Analysis

If Jules Vern expressed the title of his famous book, “Twenty Thousand Leagues Under the Sea” in feet, what would the title be?

(1mile = 5280ft, 1 League = 3.450miles)

Practice Problem

• During surgery, a patient received 5.0 pints of plasma. How many mL of plasma is this? (1L = 1.057qts, 2 pints = 1qt)

A. 2400mL

B. 2.4mL

C.4700mL

D.4.7mL

Dimensional Analysis

If a particular fad diet claims a weight loss of 3.0 pounds per week, how many grams per day would this be? (1lb = 453.6g)

A. 1400 g/day

B. 0.046g/day

C. 190 g/day

Converting from squared units to squared units or cubed units to cubed units

• Warning: This type of conversion gives many students difficulties!!!!!

• The one thing you have to remember:– What does it mean to say that a unit is squared or

cubed?– m2 = m x m; s3 = s x s x s

• When there are squared or cubed units, you have multiple units to cancel out!

Examples

• Convert 127.4 cm3 to m3.

(100cm = 1m)

• Convert .572 miles2 to km2.

(1km = .621miles)

Percent Factor in a ProblemIf the thickness of the skin fold at the waist indicates an 11% body fat, how much fat is in a person with a mass of 86 kg?

percent factor

86 kg mass x 11 kg fat

100 kg mass

= 9.5 kg fat

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Even MORE Practice with Conversion Factors

• A lean hamburger is 22% fat by weight. How many grams of fat are in 0.25 lb of the hamburger?

Density

• A ratio of the mass of an object divided by its volume

Density = Mass/Volume

• Typical units = g/mL (NOTE: 1mL=1cm3)

Measuring Density in Lab

Measuring Density in Lab

68.60g = 68.60g(45.0mL - 35.5mL) 9.5mL

Measuring Density in Lab

68.60g = 68.60g = 7.2g/mL(45.0mL - 35.5mL) 9.5mL

Densities of Common Substances

Sink or Float• Ice floats in water

because the density of ice is less than the density of water.

• Aluminum sinks because its density is greater than the density of water.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Sink or Float• Ice floats in water

because the density of ice is less than the density of water.

• Aluminum sinks because its density is greater than the density of water.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Which diagram correctly represents the liquid layers in the cylinder? Karo (K) syrup (1.4 g/mL), vegetable (V) oil (0.91 g/mL,) water (W) (1.0 g/mL)

A B C

K

K

W

W

W

V

V

V

K

Learning Check

A)

Vegetable oil 0.91 g/mL

Water 1.0 g/mL

Karo syrup 1.4 g/mL

K

W

V

Solution

Osmium is a very dense metal. What is its density in g/cm3 if 50.0 g of osmium has a volume of 2.22 cm3?

a) 2.25 g/cm3

b) 22.5 g/cm3

c) 111 g/cm3

Learning Check

Osmium is a very dense metal. What is its density in g/cm3 if 50.0 g of osmium has a volume of 2.22 cm3?

a) 2.25 g/cm3

b) 22.5 g/cm3

c) 111 g/cm3

50.0g = 22.5g/cm3

2.22cm3

Learning Check

Density can be written as an equality. • For a substance with a density of 3.8 g/mL, the equality is:

3.8 g = 1 mL

• From this equality, two conversion factors can be written for density.

Conversion 3.8 g and 1 mL factors 1 mL 3.8 g

Density as a Conversion Factor

DENSITY PRACTICE

The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane?

A) 0.614 kg

B) 614 kg

C) 1.25 kg

Learning Check

Density Example

• You have been given 150g of ethyl alcohol which has a density of 0.785g/mL. Will this quantity fit into a 150mL beaker?

A. YES B. NO

A group of students collected 125 empty aluminum cans to take to the recycling center. If 21 cans make 1.0 lb aluminum, how many liters of aluminum (D=2.70 g/cm3) are obtained from the cans?

A) 1.0 L B) 2.0 L C) 4.0 L

Learning Check

31

Temperature

Temperature

• Is a measure of how hot or cold an object is compared to another object

• Indicates that heat flows from the object with a higher temperature to the object with a lower temperature

• Is measured using a thermometer

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Temperature Scales

Solving a Temperature Problem

A person with hypothermia has abody temperature of 34.8°C. What isthat temperature in °F?

TF = 1.8 TC + 32

TF = 1.8 (34.8°C) + 32° exact tenths exact

= 62.6 + 32° = 94.6°F tenths Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

Converting between Temperature Scales

• ***Conversions between Celsius and Kelvin– (Temperature in K) = (temperature in oC) + 273

– (temperature in oC) = (temperature in K) – 273

• Conversions between Celsius and Fahrenheit– oF = 9/5 (oC) + 32

– oC = 5/9(oF – 32)

Chemistry is the study of Matter

Matter is anything that has mass and

takes up space.

Chemistry is the study of Matter

Matter has both physical and

chemical properties

Physical Properties

Physical properties are:

• Characteristics observed or measured without changing the identify of a substance.

• Shape, physical state, odor, boiling and freezing points, density, and color of that substance. (Changes of state)

Chemical Properties

Chemical properties describe the ability of a substance

• To interact with other substances• To change into a new substance

Example:

Oxygen reacts with methane

Gas to form carbon dioxide & water

Matter Classified

Matter

Pure Substance Mixture

Matter Classified

Matter

Pure Substance Mixture

Classification of Matter

• Pure Substances: A form of matter that always has a definite and constant composition. Properties always the same under a given set of conditions (temperature & pressure)

Matter

Pure Substance Mixture

Element Compound

Pure Substances: Elements

• Element – Pure substance that can not be broken down into simpler

substances by chemical means.

Copper (Cu)Lead (Pb)Aluminum (Al)

– The most basic form of matter.– Each element can be found on the periodic table.

Periodic Table of Elements

Names and Symbols of the Elements

• Each element has a unique name and is represented by a unique symbol

– Chemical symbol: a one- or two-letter designation for an element derived from the element’s name

– First letter of the symbol is always capitalized

Several symbols are derived from Latin names as shownbelow:

Cu, copper (cuprum) Au, gold (aurum)

Fe, iron (ferrum) Ag, silver (argentum)

Symbols from Latin Names

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Select the correct symbol for each:1. Calcium

A) C B) Ca C) CA

2. Sulfur A) S B) Sl C) Su

3. Iron A) Ir B) FE C) Fe

Learning Check

Select the correct symbol for each:

1. Calcium B) Ca

2. Sulfur A) S

3. Iron C) Fe

Learning Check

Select the correct name for each symbol:1. N

A) neon B) nitrogen C) nickel

2. P A) potassium B) phlogiston C) phosphorus

3. Ag A) silver B) agean C) gold

Learning Check

Select the correct name for each symbol:1. N

A) neon B) nitrogen C) nickel

2. P A) potassium B) phlogiston C) phosphorus

3. Ag A) silver B) agean C) gold

Learning Check