Introduction to Chemistry

• http://www.youtube.com/watch?v=izeuGr0lbN0

What is Chemistry?

•The study of the composition of matter and the changes that matter undergoes

Five major branches of chemistry•Organic

•Inorganic

•Analytical•Physical•Biochemistry

Why study Chemistry???

•Pure Chemistry•Applied Chemistry (Technology)

Chemistry plays a big part in our lives•We are in the “Age of Plastics”

•High “strength to weight” ratio

Energy•New fuels•New insulation material

•Energy from the sun•Hydrogen cells•Storage batteries

Medicine and Biotechnology•Medicines•Surgical breakthroughs•Genetic research

Agriculture•Protect crops• Increase food supply• Increase strength and vitality of plants

Environment•Pollution•Catalytic converters•Acid rain•Ozone layer

SCIENTIFIC METHOD

1. Observation Gather data:

qualitative or quantitative

2. Hypothesis• tentative explanation for what is observed (educated guess)

3. Experiments – set of controlled observations that test a hypothesis

–Independent variable – one you are going to change

–Dependent – changes depending on the independent variable

–control – standard for comparison

–Model – visual, verbal and/or mathematical explanation of experimental data

Conclusion•– judgment based on the information obtained

Theory•– explanation that has been supported by MANY experiments

Scientific Law•– describes a relationship in nature that is supported by many experiments.

Types of observations

Qualitative observations – describe a substance without using numbers

“It is heavy” “ It is blue” “It smells”

Quantitative observations – use numbers

87 millimeters 10 liters 4.0 g/ml

Scientific Notation

765,000,000,000 7.65 X 1011

Move decimal to the left – is positive

0.0000084 8.4 X 10-6

Move decimal to the right – is negative Samples on handout

Write in standard notation

4.5 x 10-5

0.000045

3.42 x 104

34200

Accuracy Is how close a measurement is to the correct or accepted value

Precision How close a series of

measurements are to each other

(how close a measurement is to other measurements of the same thing)

Dartboard example

Significant figures Assures the certainty of

measurements

For any measurement, scientists only record all the digits they are certain of, plus one estimated figure

Together, they are called “significant figures”

Sample

• 6.2345 meters• All the digits are significant. Which one

is the estimated and which are certain?

• 6,2,3,4 are certain• 5 is estimated

A scientist measures 89 seconds

All are significant Which are certain and which are

estimated?

8 is certain 9 is estimated

RULES FOR COUNTING SIGNIFICANT FIGURES IN A MEASUREMENTRule 1 – all nonzero digits are

significant – 1,2,3,4,5,6,7,8,9 – are significant

Rule 2 – Final zeroes to the right of the decimal point are significant

3.4000 5 sig figs

Rule 3 – zeroes between two significant digits are significant

304 3 sig figs70009 5 sig figs

Rule 4 – zeroes used for spacing the decimal point are not significant

0.00045 2 sig figs 0.02387 4 sig figs

Rule 5 – for numbers in scientific notation, all of the digits before “x 10x” are significant

5.730 x 109 4 sig figs

Be careful of this one

7000 1 sig fig 7000. 4 sig figs

Let’s practice!!

135.3 4 sig figs 4.6025 5 sig figs 200,035 6 sig figs 0.0000300 3 sig figs

2.0000300 8 sig figs 0.002 1 sig fig 4.44 x 103

3 sig figs 2.0 x 10-2

2 sig figs

10.00 4 sig figs 10 1 sig fig 102,000 3 sig figs

Solving problems with sig figs

Multiplying and dividing with sig figsThe answer you get must be

rounded to the same number of sig figs as the measurement with the lowest number of sig figs (that you multiplied or divided)

Example

Multiply 4.610 feet by 1.7 feet. Express your answer in correct sig figs

4.610 x 1.7 = 7.837 How do you round it? 4.610 has 4 sig figs 1.7 has 2 sig figs Round answer to 2 sig figs Answer = 7.8 square feet

Divide 653 miles by 3 hours. Express in the correct number of sig figs

Answer = 200 miles/hour

Adding and Subtracting with sig figs

When adding or subtracting measurements, the answer cannot have more certainty than the least certain measurement.

Answer must have the same number of sig figs to the right of the decimal point as the measurement with the fewest sig figs to the right of the decimal point

Example

4.271 grams (3 sig figs to the right of decimal) 2 grams (0 sig figs to the right of decimal) + 10.0 grams (1 sig fig to the right of decimal) 16.271 grams round 16 grams

Sample

Add these measurements: 4.35 seconds and 212.2 seconds. Express

your answer using correct sig figs Answer = 216.6 seconds Add these measurement: 2.423 meters + 0.001365 meters Answer = 2.424 meters

Measurement units and unit conversions

• Common metric base units:• Distance or length – meter m• Mass – gram g• Volume – liter L• Temperature – degree Celsius oC• Time – second s

• Also use Kelvin (K) for temperature

Metric Prefixes

Common metric prefixes

• Micro

• Example 1 μm = 0.000001 m

1 x 106 μm = 1 m

milli m• 0.001 or (1 x 10-3)• Example• 1 mg = 0.001 g• 1000 mg = 1 g

centi c•0.01 or ( 1 x 10-2)•Example•1 cm = 0.01 m•100 cm = 1 m

Deci d• 0.1 or (1 x 10-1)• Example• 1 dL = 0.1 L (liter)• 10 dL = 1 L

kilo k• 1000 or (1.0 x 103)

• Example

• 1000 g = 1 kg

Unit Conversions

Also called “factor labeling”• How many inches in 2 feet?• How many feet in 36 inches?• You just did a unit

conversion!!!!!!• Look at board

Must use correct “conversion factor”

• 230 cm = ? m• Must know that 100 cm = 1m• Write possible conversion factors• 1m or 100 cm 100 cm 1 m

Write the number you are converting first

• Multiply it by the conversion factor that has the unit you want your answer to be in on the TOP

• This guarantees that you will divide or multiply when you are supposed to.

• 230 cm x 1 m = 2.3 m 100 cm

The top and bottom units cancel out and the only unit left is the one you want you answer to be in!!!!!

• Text – practice on pgs. 36 -37

• Show you two step conversions on board

• 4500 cm = ? km

Derived units What does “derived” mean?

A derived unit is a measurement unit created by multiplying or dividing other units

Miles per hourwords per minute

AreaAreaLength x widthft x ft = ft2 ft2 is a derived unit (derived from two

length units)m x m = m2 m2 is a derived unit (derived from two

length units)

VOLUME Length x width x height

ft x ft x ft = ft3

m x m x m = m3

cm x cm x cm = cm3

DENSITY Describes how dense something is How heavy it is for its size

Density = mass divided by volume D = M V M = D x V

V = M D

Since you are dividing two different measurements, the unit for density is a DERIVED UNIT.

Derived from a mass measurement and a volume measurement

g/mL g/L

DENSITY PROBLEM Calculate the density of a substance

with a mass of 24.3 g and a volume of 32.9 mL. Use the correct unit and the correct number of sig figs in your answer.

D = M V D = 24.3 g 32.9 mL Ans. = 0.739 g/mL

PROBLEM What is the volume of an object with

a density of 1.25 g/mL and a mass of 281 g?

V = M D V = 281 g 1.25 g/mL g cancels, so units are mL for answer V = 225 mL

NOW YOU DO SOME PROBLEMS! Text – Pg. 46 #20, 21 Pg. 47 #25