What is Chemistry ? What is Chemistry ?

 Chemistry is the study of all substances and the changes that they can undergo.  Chemistry has been called the central science because it overlaps many other sciences.  Biologists, Geologists, etc. all use chemistry in their work.

What is Chemistry ?  Chemistry is wherever there is change.

Chemistry  Hair stylists and construction workers need knowledge of some chemistry.

Chemistry cont’d Chemistry cont’d  Hairstylists use the same chemicals found in many chemical labs to get their desired results.  Chemistry is used to 1)Examine a wetlands habitat. 2)Preserve historical artifacts.

Scientific Method  What is the scientific method ? The scientific method is a way of answering questions about the world we live in. The scientific method is a way of answering questions about the world we live in.  Make an observation  Come up with a question & produce a hypothesis  Test it with an experiment  Analyze your experiments data to see if it agreed with your hypothesis or theory.  Restructure your experiment and try again.  Continue with the above steps until it becomes a Law.

Hypothesis vs. Theory  What is the difference between a hypothesis and a theory ?  A hypothesis is a first thought about the solution to the problem. It usually doesn’t have any experimental proof.  A theory is developed after some experimentation is done and so it has some evidence to back it up.  A theory comes after the hypothesis.

A Scientific Law  So when does a theory become a Law ?  Let’s take a look at Newton’s Law of Gravity.  He quickly proved that there was a definite relationship in the rate of falling objects.  It became a Law when he was able to describe that relationship so well, that other people were able to duplicate what he did and get the same results.

More Scientific Method  In an experiment, there is a variable: which is the factor being tested.  Experimental control: control responds in a predictable way to the experiment.  Only the variable is allowed to change in a good experiment.

Here’s an example !  Suppose I wanted test scores to go up. So I made the next test all long essay problems. When I graded the next test, the grades did go up.  CAN I BE CERTAIN THAT IT WAS BECAUSE OF THE ESSAY TESTS ?

The Answer ????  The answer is no.  Other variables were also changing.  The test was over other material so this chapter just could have been easier than the last one.  The students could have studied more.  More time could have been spent on this chapter.  All of the other variables would have had to remain the same to be certain as to the reason for the improved scores.

Experiments  Experiments include thought and variables.

Lab Safety  Safety in the lab is of utmost importance:  Failure to follow lab safety rules will result in a failing score for the lab and perhaps further penalties.  There are many lab rules. Here are some of the more important ones. -Follow directions at all times. -Notify if any problems -Wear safety goggles at all times -If it’s hot, let it cool -Carry chemicals with caution -Dispose of chemical wastes properly

Measuring in Science  Metric System: International system of measurement. -Length: Meter (m) -Mass and Weight: Kilogram (kg) -Area and Volume: derived units. Cubic meter (m 3 ) ex- area rectangle: length X width

More Measurements

Metric Prefixes  Metric Prefixes: Attached to the beginning, creating more easier to use units. Attached to the beginning, creating more easier to use units. K H D m d c m Kilo Heca Deca (meter) deci centi milli

Uncertainty  Uncertainty in measurement: Measuring is never completely free of flaws and always involves some estimations.

Precision v. Accuracy  Precision: -A reliable measurement will give about the same result again and again under the same conditions. -A reliable measurement will give about the same result again and again under the same conditions. -Accuracy: A result that is close to the accepted value. Ex: A dart board. A result that is close to the accepted value. Ex: A dart board.

Precision and Accuracy  This is an example of precision and accuracy, where the darts land on the board.

Scientific Notation  Scientific notation: Making long numbers easier to write by multiplying them to the 10 TH power. Example: -1,700,000,000,000,000 = 1.7x = 9.85x10 -18

Percent Error  Percent error: Percent error= Measured value * accepted value Percent error= Measured value * accepted value accepted value X100% -ratios: speed= distance time

Density  Population density = population area Density= mass volume Example: D=75g 22cm 3 = 3.4g/cm 3 22cm 3 = 3.4g/cm 3

Significant Digits  Significant Digits: The certain digits and the estimated digits of a measurement are together. The certain digits and the estimated digits of a measurement are together.

More on Significant Digits  Atlantic Pacific Rule: A rule that can help you identify the significant digits in a measurement. A rule that can help you identify the significant digits in a measurement. A)Decimal present, count from the Pacific side. B)First nonzero digit C)All other digits are significant.

Atlantic Pacific Rule 

Dimensional Analysis  Dimensional analysis: The technique of converting between units. The technique of converting between units. Unit Equality: An equation that shows how different units are related.

Conversion Factors Conversion Factors  Conversion factors: Fraction having a value of one that is written from a unit equality and is used to change a measurement from one unit to another.

More on Conversions  How to do conversions: 1 gal = L (Cross Multiply) 1 gal 1 gal 1 = 3.78 L 1 = 3.78 L 1 gal

Problem Solving  4 step problem solving strategy: 1) Analyze 2) Plan 3) Solve 4) Evaluate

Graphing  Graphing: 1) label each axis with name and variable in units of measurements 1) label each axis with name and variable in units of measurements 2) Make a title 2) Make a title 3) Plot the points 3) Plot the points 4) connect the data points with the best fit line 4) connect the data points with the best fit line

Graphing Graphing

Ways of Showing Data