Chemistry

• the study of matter and energy

• the study of the composition of substances and the changes they undergo.

Scientific MethodA logical approach to solving problems

1. Define a problem / ask a question2. Research the Problem

• Look things up (internet, books, journals)• Do Interviews• Make observations using your five senses

3. Form a Hypothesis• An educated suggestion/answer to the problem• Must be specific and measurable (testable)• Typically an if-then statement

Scientific Method4. Experiment

• Make observations, take measurements, and gather data to test your hypothesis

• The experiment needs to be reproducible

Independent Variable – one “thing” you are changing in your experiment (can only have one)

Dependent Variable – one “thing” you are measuring in your experiment – depends on the independent variable (can only have one)

Control – everything that is not being changed or being tested

Scientific Method

5. Conclusion• Explain how your data either supports your hypothesis

or does not, provide reasons for failure

6. Share Results. Modify• Communicating your results with your peers or fellow

scientists helps confirm or deny your hypothesis.• Modify your hypothesis and retest if necessary

Which color of M&M’s is the most abundant in a typical package of M&M’s

Together:•Research•Hypothesis

In groups?•Experiment (data table)•Analysis (graph)•Conclusion (write up)

Theory vs. LawTheory – explains WHY something is; can be repeated,

but not proven.

Scientific Law – description of what is happening, does NOT explain why.

Ex: A balloon expands in the hot sunTheory – Increasing the heat of gas particles,

increases the speed &the number of collisions. This increases the volume.                                   

Scientific Law – the volume of a gas is directly proportional to the temperature if the pressure is kept constant.

Theory vs. Law

• Are based on observations

• Testable explanations that have not been proven

• Have evidence to back the claim

• Repeatedly verified over a long period of time

• Explains why something is

• Are based on facts• Have been proven• Have evidence and

results to support the proof

• Does NOT explain why• Description of what is

happening• Statement of a

relationship or a regularity

THEORY LAW

Measurments

• Made in everyday life & science• measurements include a number & a unit• Qualitative vs. Quantitative Measurements• Qualitative - a descriptive, non-numerical form. • It takes a long time to walk home. • Quantitative Measurement –a number with

units. • It takes 37 minutes & 20 seconds to walk home.

Measurement: International System of Units (SI) Open to Table 1 – pg 34 of text

• Length – metric unit is the meter (m)• Mass – the quantity of matter an object contains.

Metric unit is Kg (1Kg=1000g)• Weight – force – measure of pull on mass by

gravity. Changes w/gravity, you weigh 1/6 of your weight on the moon.

• Volume – the space occupied by matter. unit is Liter (L)

Volume of a cube or rectangle: V= l x w xh

Common items not in notes

• A penny is exactly 2.5 g• nickel weighs exactly 5 g

• A doorknob is about 1 m high.

Volume and water• 1 milliliter is the same volume as 1 cubic

centimeter.

• 1 mL of water has a mass of 1 g

• 1 L of water has a mass of 1 kg

Glassware for measuring liquid volume:

Beaker Graduated Erlenmeyer flask cylinder

Density- mass ÷ volume (g/ml) or (g/cm )• Density –how tightly the atoms are packed together.

• Most solids are denser than their liquids.

• However…water is an exception.

Water molecules

Water molecules expand in their solid form.This makes them less dense so they float in their liquid!!

Metric Prefixes: used to express very large or very small numbers.

Kilo – 1000 times larger = x103       

Hecto – 100 times larger = x102                       

Deca – 10 times larger = x101                       

deci – 10 times smaller = x10-1                       

centi – 100 times smaller = x10-2                       

milli – 1 000 times smaller = x10-3     

micro – 1 000 000 times smaller = x10-6                       

nano – 1 000 000 000 times smaller = x10-9

COPY WHAT I DO ON THE OVERHEAD!!

Dimensional Analysis

• Conversion Factor – any fraction in which the numerator equals the denominator

Ex: 1 foot=12 inches or 1 foot

12 inches

• Dimensional Analysis – using the conversion factor to change one unit into another unit

• Example: convert 36 inches into feet

36 inches x 1 foot = 3 feet 1 12 inches

Dimensional Analysis (continued)

• Note: Units that you want to cancel go in the denominator of the conversion factor. Always put the given number and units that you are changing over 1.

• Multiple Step Problems –more than 1 conversion factor

• Given (con. factor)(con. factor)(con. factor) = wanted• Example: convert 15 days into minutes

15 days x 24 hours x 60 minutes = 21,600 minutes

1 1 day 1 hour

Lets practice from our homework:

• Open book to pg 42