Chemistry UNIT 1

Susie SmithAugust, 2010

Chemistry is the study of matter.

Scientific Method

A logical method of problem solving.

Steps of the Scientific Method

Making observations that lead to a question. Forming a hypothesis to answer the

question. Testing the hypothesis by experimentation. Making a conclusion based on the results.

Definitions

Observation- use of senses and devices in the lab to obtain information.

Conclusion- a statement based on observations and prior knowledge.

Types of observations

Quantitative- includes numbers and units. Qualitative- does not include numbers and

units. Examples-

Hypothesis- an educated guess

Explains an observation. Can be tested. Will predict an outcome. Must be written as a statement.

Experiment

Designed to test an hypothesis. Involves variables Is performed under controlled conditions.

Variables

Variables are factors that can be changed.– Control variable is a variable that is held constant.– Manipulated or independent variable is changed

by the scientist.– Responding or dependent variable changes as a

result of the experiment.

International System (SI)

Measuring system used in science (also called the MKS)

Length

Distance between two points Base Unit- Meter (m) Instrument- meter stick or metric ruler

Mass

Amount of matter in a substance Base Unit- gram SI Unit – kilogram Instrument- triple-beam balance

Volume

Amount of space an object occupies Base Unit- liter (L) Instrument- metric ruler or graduated cylinder

Time

Interval between two occurances Base Unit- second (s) Instrument- stop watch

Temperature

Average kinetic energy Base Unit- Celsius (oC) or Kelvin (K) Instrument- thermometer.

Scientific Notation

Numbers are expressed in this form: M X 10n

M is a number between 1 and less than 10.

And n is equal to an exponent.

How to take numbers out of scientific notation

1 X 103 = 1000 Positive exponents move the decimal

place to the right n spaces. 1 X 10-3 = .001 Negative exponents move the decimal

place to the left n spaces.

Scientific Notation

6.2 X 104

1.5 X 10-2

2.4 X 10-5

7.06 X 106

6.0 X 106

How to put numbers into Scientific Notation

6,011,000 0.058 24 0.009009 6.734114

Conversion Factors

One large unit = how many smaller units. One dozen = 12 units.

Common Conversions

“Prefix Abbreviation Conversion fact

Mega M 1Mm = 1,000,000 m

Kilo k 1km = 1,000 m

Deci d 1m= 10dm

Centi c 1m= 100cm

Milli m 1m= 1,000 mm

Micro 1m= 1,000,000 m

Conversions

Start every problem with the original amount.

Then use a conversion fact to convert the units of measurement to what you need.

Set up every problem as a fraction with the unit you are looking for on top and the unit you started with on bottom.

Practice Problems

1 kg = ________ g 1s = _________ ds ________ = 1 L ______ dollars = 100 centidollars 100 dg = _____ g

How to work your calculator?

Look for EE, X10, or ^ keys on your calculator

Every calculator is different. Make notes about how to use your

calculator.

Practice

Convert 152 cm to m. Use the conversion fact 1m = 100cm 152 cm X 1m = 1.52 m

100 cm

Conversion Practice

Convert 62 kg to _________ g. Convert 1700 m to _______ m Convert 0.0056 mm to ______km.

Conversions with Derived Units

Convert 570 g/L= __________ g/mL 16 m/min = ______________ m/s Convert 65 km/h =____________ m/s

Order of operations

Please Excuse My Dear Aunt Sally. Parenthesis Exponents Multiply or Divide Addition or Subtraction

Definitions

Accuracy- closeness of a measurement to the accepted value

Precision- the reproducibility of a measurement

Significant Digits

All measured digits plus 1 estimated digit Read the smallest division on the instrument

and then estimate one more digit 3.21 cm, _____ significant digits, ____

measured and ___ is estimated.

Zeros and significant digits

Zeros are placeholders. They are only significant if they are in between

two non zero numbers. 906 They are significant if they follow a non zero

number and are after a decimal. 15.00 They are not significant if they are before a

decimal and before a non zero number. 0.0015 They are significant if a bar is placed on top of

the 0.

Rules for rounding

After multiplying or dividing– Round to the least number of significant digits– Round to the weakest link.– Ex. 420 X 100 = _________

Rounding

After adding and subtracting,– Round answer to 1st column containing an

estimated digit– Round to the weakest column

12.001

4.02

+ 3

19.021 19

Rule of 5’s

When a number is exactly half way between two numbers, always round to the even number.

12.5 rounds to 12 11.5 rounds to 12 12.5001 rounds to 13

Scientific Method

Variable- a physical quantity which can change in the experiment

In a good experiment, only one variable is allowed to change.

Parts of an Experiment

Manipulated (independent) variable- is changed by the experimentor

Responding (dependent) variable- depends on the results of the experiment

Control variables- are variables that are held constant on each group.

Weight verses Mass

On the moon, your mass would not change, and your weight would change.

Mass- is the amount of matter an object has– kilograms

Weight- is the affect of gravity pulling on an object– Newtons

Scientific Method

Question Hypothesis Research Experimentation Conclusion Retest

Graphing scientific data

X axis- independent variable Y axis- dependent variable means “is directly proportional to”

Straight Line Graph y x

y = kx , where k is a constant Slope is y/x or rise/run

Inverse proportion y 1/x

y = k/x Graph is a hyperbola

Equations

When the variables of an equation are on the same side of the equal sign, the variables are inversely proportional.

When the variables of an equation are on opposite sides of the equal sign, the variables are directly proportional.

P A = F