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Welcome to Pre-AP Chemistry

Agenda for Class 1

Introduction

Seating Assignments

Distribution of Books and Chapter 1 and 2 Handouts

Discussion of Class Rules

Assignments for Chapter 1

Demonstrations

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Introduction

Syllabus Discussion

Grades

Assignments/Homework

Opportunity for Questions About Dr. Lutz

Three Interesting Things About You

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Experimental DesignHypothesis

The statement of the hypothesis should include some attempt to explain the cause for what you observe and should include quantities that are measurable (variables). For example:

The amount of fertilizer used will impact how fast and how large plants will grow.

Designing an Experiment

Amount of fertilizer is the independent variable (we choose how much to use).How fast and how large are dependent variables (depend on how the plants respond to the fertilizer)

A quality design must be able to determine whether (and by how much) changing the independent variable impacts the dependent variable. In addition, the experiment must be repeated several times to show that the results are reproducible. Lastly a quality design must have something to compare to (called a control) in order to show that any changes in the dependent variable came about because of the independent variable and not other outside factors.

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Example:

Hypothesis: The amount of salt that you can dissolve in water will increase when the temperature of the water is higher than room temperature.

Proposed experimental design:

Step 1: measure the number of grams of salt that dissolve in 1.0 L of water at 22oC (normal room temperature).

Step 2: measure the number of grams of salt that dissolve in 1.0 L of water at 35oC.

Repeat Steps 1-3 several times and use the average number of grams of salt measured.

Step 3: measure the number of grams of salt that dissolve in 1.0 L of water at 45oC.

Problems: A) Identify the independent variable(s)

B) Identify the dependent variable(s)

C) Which step or steps would be identified as the control?

D) What is the purpose of repeating steps 1-3 several times?

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Laboratory activity: Paper Helicopter

Goals:

Change the design of a paper helicopter so that it will stay in the air longer than the standard paper helicopter.

Perform experiments to determine what effects your design changes had on the flying time of the paper helicopter.

Materials: Paper helicopter sheet, Scissors Tape

Watch

Conclusion:

Identify the variables in your experiments (dependent and independent).Identify the control you used in your experiments.

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Bonus Problem:

Briefly describe experiments (i.e. write out steps) that could be used to test the hypothesis below. Afterwards, clearly identify the independent variable(s), the dependent variable(s), and the control experiment.

Hypothesis: The time it take for a fixed amount of salt to dissolve in water depends upon the amount of water and the amount of stirring.

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Chapter 1: Introduction to Chemistry

Objectives: The student will be able to:

identify and analyze two or three ways in which chemistry impacts daily life;

understand and follow safety procedures in the laboratory and in emergencies;

incorporate new vocabulary into discussions;

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Chemistry:

Chemistry is the study of matter and the changes in energy involved when matter changes forms.

However, heat and light are components of many chemical reactions!

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What does “weightless” mean?

How is it possible to be weightless?

Can we compare and contrast the terms “mass” and “weight”?

Mass is a measure of the quantity of matter that is present.

Weight is a measure of the force of gravity on a mass.

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Matter:Matter is anything that has mass and takes up space (has a volume). Matter is often made up of small pieces called atoms or molecules.

Mass and Weight are not the same thing.

For example, an object that has a mass of 1.0 kg will have a weight of 1.0 kg on the surface of the earth but would only have a weight of 0.17 kg on the moon. However, the mass would be 1.0 kg on both the earth and the moon.

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Earth Moon

On a balance, mass = 1.0 kg

On a balance, mass = 1.0 kgOn a scale, weight = 1.0 kg

On a scale, weight = 0.17 kg

A balance works in a different way than a scale.

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“Atoms” vs. “Molecules”

Atom: smallest particle of matter that can be recognized as a specific element.

Molecule: combination of two or more atoms.

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Oxygen and Hydrogen Molecules

Ozone would be written as O3

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A “Chemical Reaction”

A chemical reaction is a process where one or more substances become different substances. In the following example, the compound water is becoming the element oxygen and the element hydrogen. Note that since there are 2 oxygen atoms in the elemental form oxygen and 2 hydrogen atoms in the elemental form of hydrogen, these two elements can also be called compounds or molecules.

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Chemical Reactions can often be performed in either the forward or reverse direction. The reaction below is in the opposite direction to the previous example. Here, oxygen is reacting with hydrogen to make water.

As an equation: 2 H2 + O2 → 2 H2O + Heat

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Law vs. Theory

• A law summarizes what happens.

• A theory (model) is an attempt to explain why it happens.

• A law is so well accepted that no one believes that it could be incorrect.

• A theory explains why something happens, but scientists believe that there may be some facts that the theory will not correctly explain.

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CFC Concentration over time

130150170190210230250270290

1975 1980 1985 1990 1995 2000

Year

CF

C C

once

ntra

tion

(ppt

)

What is unusual about this graph?

Graphing is a common method used to summarize experimental data.(see the graph below from data in Chapter 1)

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What information is being graphed here?

What is the independent variable?

What is the dependent Variable?

Independent Variable is the one you choose to change (should be plotted on the x axis)

Dependent Variable is the one that changes on its own (should be plotted on the y axis)

y = 9.75(x) 19143

Equation for the line is:

What does slope mean here?

CFC Concentration before 1991

130

150

170

190

210

230

250

270

1976 1978 1980 1982 1984 1986 1988 1990 1992

Year

CF

Con

cent

rati

on (

ppt)

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CFC Concentration After 1990

269

271

273

275

1991 1992 1993 1994 1995 1996 1997

Year

CF

C C

once

ntra

tion

(pp

t)

y = x 1722

Equation for the line is: How does the slope of the line compare to the previous one and what does that imply?

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Branches of Chemistry:

Organic Chemistry

Inorganic Chemistry

Physical Chemistry

Analytical Chemistry

Biochemistry

Study of compounds containing carbon.

Study of compounds that do not contain carbon.

Study of energy changes associated with chemical and physical changes.

Quantification of the amount of a substance present in a mixture.

Study of chemistry that occurs in living systems.

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