Chapter 1Introduction to Chemistry

1

1.1 The Scope of Chemistry

What is chemistry? is the study of the composition of matter and

the changes that matter undergoes. Matter – anything that has mass and

volume Volume – amount of space an object occupies Mass – amount of matter an object contains Weight – pull of gravity on an object

(proportional to mass and force of gravity).

2

Branches of Chemistry Organic chemistry – study of carbon containing

chemicals Inorganic chemistry – study of matter that

does not contain organic chemicals Physical chemistry – the area that deals with

the mechanism, rate, and energy transfer that occurs when matter undergoes change

Analytical chemistry – study that focuses on the composition of matter

Biochemistry – study of matter and processes of living organisms.

1.1 The Scope of Chemistry

3

Pure Chemistry: The pursuit of chemical knowledge for its own sake. Study to understand

Applied Chemistry: Research that is directed toward a practical goal or

application. Study to use

1.1 The Scope of Chemistry

Alexander Fleming used pure then applied chemistry to understand mold growth.

4

Technology: The means by which a society provides its members

with those things needed and desired. Examples of modern research in chemistry

technology: benefit the environment conserve and produce energy improve human life expand our knowledge of the universe.

1.2 Chemistry and You

5

1.3 Thinking Like a Scientist

Scientific Method Logical, systematic approach used

to understand the world around us.

Observation

Hypothesis

Experiment

Conclusion(theory or law)

A HYPOTHESIS CAN NOT BE

PROVEN CORRECT!

IT CAN ONLY BE PROVEN WRONG!

6

1.3 Thinking Like a Scientist

Understanding the parts Observations: using

senses to obtain data Qualitative data –

descriptive, nonnumeric information. Color, odor, texture, or “hot” and

“cold” Quantitative data – definite

numerical information. 38 °C, 24.5 m , or 4.1 × 1015 Hz

7

Hypothesis Proposed explanation for an observation or

“educated guess” Written as an “If and then” statement

Experiment Procedure used to test hypothesis Independent variable – the variable that

will be changed; what the scientist controls/manipulates

Dependent variable – the variable that is observed; responds to independent variable

Constants – the other factors that are not allowed to change.

Control – standard used for comparison

1.3 Thinking Like a Scientist

8

Class Example 1:Example: An experiment is designed to test

the hypothesis that “If table salt is placed in hot water, then it will dissolve faster in hot water than in room temperature water.”

Hypothesis:_______________________Independent variable:Dependent variable:Constants:Control:

1.3 Thinking Like a Scientist

temperature

rate of dissolving

amount of salt, water, and stirring

rate room temp water dissolves9

Class Example 2: Class Example 2: Sandra thought that all colas tasted the

same, but her friends seemed to have favorite brands. She decided to see if people could really taste the difference between brands of cola. At the local grocery store she purchased 2 liter bottles of Coke, Pepsi, and a generic brand sold there. She got 10 of her friends together at her house for the test. Each person was asked which cola they preferred and then given three unmarked cups of cola to taste. Each cup contained 50 mL of cola. Sandra recorded how many of the people actually picked the cola they said was their favorite.

Class Example 2:

Independent variable:_______________ Dependent variable:________________ Constants:____________________ Control:______________________

brand

choice of favorite

same friends, 50mL cola & unmarked cups

Generic brand

Conclusion Theory – tested explanation for a broad set

of observations explanation of WHY something occurs. Ex: Einstein’s theory of relativity, Atomic theory,

Kinetic theory, and Quantum theory Model – visual, verbal or mathematical

explanation that needs extensive testing to become a “theory”.

Law – a concise statement that summarizes the results of many observations and experiments

summary of WHAT will occur. Newton’s First Law (gravity) and Law of

Conservation of mass based on what has already happened

1.3 Thinking Like a Scientist

12

1.3 Thinking Like a Scientist:The Scientific Method

ExperimentsAn experiment can lead to observations that support or disprove a hypothesis.

TheoryA theory is tested by more experiments and modified if necessary.

HypothesisA hypothesis may be revised based on experimental data.

Observations

Scientific LawA scientific law summarizes the results of many observations and experiments.

13

14

Graphing

• A graph is a visual display of data.

• Using data to create a graph can help to reveal a pattern if one exists.

15

Circle Graph• A circle graph is

sometimes called a pie chart because it is divided into wedges like a pie or pizza.

• A circle graph is useful for showing parts of a fixed whole.

• The parts are usually labeled as percents with the circle as a whole representing 100%.

16

Bar Graph• A bar graph often is used

to show how a quantity varies with factors such as time, location, or temperature.

• In those cases, the quantity being measured appears on the vertical axis (y-axis).

• The independent variable appears on the horizontal axis (x-axis).

• The relative heights of the bars show how the quantity varies.

17

Line Graph• In chemistry, most

graphs that you create and interpret will be line graphs.

• The points on a line graph represent the intersection of data for two variables.

• The dependent variable is plotted on the y-axis and the independent variable on the x-axis.

• The independent variable is the variable that a scientist deliberately changes during an experiment.

18

Line Graph

• Sometimes points are scattered, the line cannot pass through all the data points.

• The line must be drawn so that about as many points fall above the line as fall below it.

• This line is called a best fit line.

19

Line Graph

• If the best fit line is straight, there is a linear relationship between the variables and the variables are directly related.

• This relationship can be further described by the steepness, or slope, of the line.

• If the line rises to the right, the slope is positive.• A positive slope indicates that

the dependent variable increases as the independent variable increases.

20

Line Graph

• If the line sinks to the right, the slope is negative.

• A negative slope indicates that the dependent variable decreases as the independent variable increases.

21

Line Graph

• Either way, the slope of the graph is constant. You can use the data points to calculate the slope of the line.

• The slope is the change in y divided by the change in x.

22

Interpreting Graphs

• When points on a line graph are connected, the data is considered continuous.

• You can read data from a graph that falls between measured points.

• This process is called interpolation.

23

Interpreting Graphs

• You can extend the line beyond the plotted points and estimate values for the variables.

• This process is called extrapolation.

• Why might extrapolation be less reliable than interpolation?• The trend might change!