Chemistry Notes

What Is Chemistry?

Chemistry is the study of composition, structure, properties, and reactions of matter.
Chemistry happens all around you every day; for example, antacid tablets undergo a chemical reaction when dropped in water.
Chemistry studies substances in terms of:
- Composition: What is it made of?
- Structure: How is it put together?
- Properties: What characteristics does it have?
- Reactions: How does it behave with other substances?

Chemistry and Matter

Matter is another word for all substances that make up our world.
- Examples of matter include: antacid tablets, water, the oxygen we breathe, the carbon dioxide we exhale, and ourselves.
Chemicals are substances that have the same composition and properties wherever found.
Chemicals are often substances made by chemists that you use every day; for example, toothpaste is a combination of many chemicals.

Chemicals Commonly Used in Toothpaste

Calcium carbonate: Used as an abrasive to remove plaque.
Sorbitol: Prevents loss of water and hardening of toothpaste.
Sodium lauryl sulfate: Used to loosen plaque.
Titanium dioxide: Makes toothpaste white and opaque.
Sodium fluorophosphate: Prevents formation of cavities by strengthening tooth enamel with fluoride.
Methyl salicylate: Gives toothpaste a pleasant wintergreen flavor.

Learning Check: Chemicals

Fruit, milk, and breakfast cereal contain chemicals that have the same composition and properties wherever found.
Sunlight is energy and, therefore, does not contain chemicals.

The Scientific Method

The scientific method is a set of general principles that helps to describe how a scientist thinks.
Steps:
- Make observations about nature and ask questions about what you observe.
- Propose a hypothesis, which states a possible explanation of the observations.
- Several experiments may be done to test the hypothesis.
- When results of the experiments are analyzed, a conclusion is made as to whether the hypothesis is true or false.
The scientific method develops a conclusion or theory using observations, hypotheses, and experiments.
The hypothesis is modified if the results of the experiments do not support it.

Everyday Scientific Thinking

Observation: You visit a friend, and soon after arriving, your eyes begin to itch, and you start to sneeze. You observe that your friend has a new cat.
Hypothesis 1: Perhaps you are allergic to cats.
Experiment 1: To test your hypothesis, you leave your friend’s home. If the itching and sneezing stop, perhaps your hypothesis is correct. If the itching and sneezing do not stop, perhaps you have a cold.
Observation: Upon leaving your friend’s home, the itching and sneezing stop.
Experiment 2: Visiting a second friend with a cat causes your eyes to itch, and you begin to sneeze again, further supporting your hypothesis.
Theory: The experimental results indicate that indeed you are allergic to cats.

Learning Check 2: Scientific Method Steps

A. A blender does not work when plugged in. (Observation)
B. The blender motor is broken. (Hypothesis)
C. The plug has malfunctioned. (Hypothesis)
D. The blender does not work when plugged into a different outlet. (Experiment)
E. The blender needs repair. (Theory)

Strategies to Improve Learning and Understanding

Success in chemistry utilizes good study habits, connecting new information with your knowledge base, rechecking what you have learned and what you have forgotten, and retrieving what you have learned for an exam.
- Do not keep rereading the text or notes.
- Ask yourself questions as you read.
- Self-test by giving yourself quizzes using practice problems in the text.
- Study at a regular pace rather than cramming.
- Study different topics in a chapter and relate the new concepts to concepts you know.

Text Features for Learning

Looking Ahead outlines the chapter topics.
Glossary and Index list and define key terms in the chapter.
Key Math Skills needed for the chapter are reviewed.
Core Chemistry Skills are indicated by icons in the margin and summarized at the end of each chapter.
Review icon at the start of a chapter Section highlights the Key Math Skills and Core Chemistry Skills needed in the current chapter.
Engage features in the margin remind you to pause your reading and test yourself with a question related to the material.
Try It First feature reminds you to work the Sample Problem before you look at the accompanying Solution.
Test suggestions in the margin remind you to solve the indicated Practice Problems as you study.
Interactive Video suggestions illustrate content as well as problem solving.

Figures and Diagrams

Many figures and diagrams use macro-to-micro illustrations:
- To depict atomic level of organization
- To illustrate the concepts in the text
- To allow you to see the world in a microscopic way

Features to Help You Study

Before reading the chapter, review the topics in Looking Ahead.
Each Section of the chapter begins with a Learning Goal which states what you need to understand.
Some Sections have a Review box that lists the Key Math Skills and Core Chemistry Skills from previous chapters that relate to the new material in the Section.
Work through each Sample Problem and compare your solution to the one provided.
Chemistry Links to Health and Chemistry Links to the Environment connect the chemical concepts you are learning to real-life situations.

Practice Problems

Practice Problems placed at the end of each Section are written to help you understand the material and give immediate applications of new ideas.
An Analyze the Problem feature shows how to organize the data in the Sample Problems to obtain the solution.

End of Chapter Summaries

At the end of each chapter are study aids, including:
- Concept Maps
- Chapter Reviews
- Key Terms
- Key Math Skills
- Core Chemistry Skills

End of Chapter Problems

At the end of each chapter you can test your knowledge further by using the:
- Understanding the Concepts problems
- Additional Practice Problems
- Challenge Problems
Every three chapters, problem sets called Combining Ideas test your ability to solve problems containing material from more than one chapter.
Answers placed at the end of each chapter give feedback to odd-numbered questions.

Make a Study Plan

Consider some of these ideas when making a plan on how to approach your studying and learning in chemistry.
- Fill in the blank reading the chapter before class
- Fill in the blank going to class
- Fill in the blank reviewing the Learning Goals
- Fill in the blank keeping a problem notebook
- Fill in the blank reading the text
- Fill in the blank trying to work the Sample Problem before looking at the Solution
- Fill in the blank answering the Engage questions
- Fill in the blank working the Practice Problems at the end of each Section and checking answers
- Fill in the blank studying different topics at the same time
- Fill in the blank organizing a study group
- Fill in the blank seeing the professor during office hours
- Fill in the blank reviewing Key Math Skills and Core Chemistry Skills
- Fill in the blank attending review sessions
- Fill in the blank studying as often as possible

Key Math Skills for Chemistry

Review math concepts used in chemistry: place values, positive and negative numbers, percentages, solving equations, and interpreting graphs.

Identifying Place Values

For any number, we can identify a place value for each digit.
Example:
- 2518 grams
  - Digit 2: thousands
  - Digit 5: hundreds
  - Digit 1: tens
  - Digit 8: ones
We can identify a place value for each digit in a number with a decimal point.
Example:
- 6.407 grams
  - Digit 6: ones
  - Digit 4: tenths
  - Digit 0: hundredths
  - Digit 7: thousandths

Learning Check 1: Place Values

Identify the place value for each of the digits in the following number: 15.24 g
- Digit 1: tens
- Digit 5: ones
- Digit 2: tenths
- Digit 4: hundredths

Positive and Negative Numbers

A positive number is any number that is greater than zero and has a positive sign (+). Often the positive sign is understood and not written in front of the number. For example: $+8$ is also written as $8$ .
A negative number is any number that is less than zero and is written with a negative sign $(−)$ . For example: $-8$ .

Multiplication with (+) and (−) Numbers

When two positive numbers or two negative numbers are multiplied, the answer is positive.
When a positive number and a negative number are multiplied, the answer is negative.

Division with (+) and (−) Numbers

The rules for division of positive and negative numbers are the same as those for multiplication.
When two positive numbers or two negative numbers are divided, the answer is positive (+).
When a positive number and a negative number are divided, the answer is negative (−).

Addition with (+) and (−) Numbers

When positive numbers are added, the sign of the answer is positive (+). For example, $3 + 4 = 7$ (the $(+)$ sign is understood).
When negative numbers are added, the sign of the answer is negative (−). For example, $(-3) + (-4) = -7$ .
When a positive number and a negative number are added, the smaller number is subtracted from the larger number. The result has the same sign as the larger number. For example, $12 + (-15) = -3$ .

Subtraction with (+) and (−) Numbers

When two numbers are subtracted, change the sign of the number to be subtracted.

Calculating a Percentage

To determine a percent, divide the parts by the total (whole) and multiply by 100%.
An aspirin tablet contains 325 milligrams of aspirin (active ingredient), and the tablet has a mass of 545 milligrams. What is the percentage of aspirin in the tablet?
A percentage $(%)$ represents the number of parts of an item in 100 of those items.
Example:
- 5 red balls / 100 balls = 5% red balls
- 50 green balls / 100 balls = 50% green balls

Solving Equations

Equations can be rearranged to solve for an unknown variable.
- Place all like items on one side.
- Isolate the variable you need to solve for.
- Check your answer.
Example:
- $2x + 8 = 14$
- Subtract 8 from each side:
  - $2x = 6$
- Divide both sides by 2:
  - $x = 3$

Learning Check 2: Solving Equations

Solve the following equation for $P_1$ :
- $P1V1 = P2V2$

Solution 2

To solve for $P1$ , divide both sides by $V1$ .
$\frac{P1V1}{V1} = \frac{P2V2}{V1}$
$P1= \frac{P2V2}{V1}$

Graphs

A graph represents the relationship between two variables. The graph below represents the volume of a gas plotted against its temperature.

Interpreting a Graph

The graph title, “Volume of a Balloon versus Temperature,” indicates that the volume of a gas is plotted against its temperature.
The vertical (y) axis label indicates that the volume is measured in liters.
The horizontal (x) axis label indicates that the temperature of the balloon is measured in degrees Celsius.
Each point on the graph represents a volume in liters that was measured at a specific temperature.
The line on the graph indicates that the volume of the balloon increases as the temperature of the gas increases. This is called a direct relationship.

Scientific Notation

Scientific notation is used to write very large or very small numbers.
- the width of a human hair, $0.000 \space 008$ meters, is written as $8 \times 10^{-6}$ meters.
- the number of hairs on a human scalp, $100 \space 000$ , is written as $1 \times 10^{5}$ hairs.
Numbers written in scientific notation have two parts: the coefficient and a power of 10.

Writing Numbers in Scientific Notation

The coefficient is obtained by moving the decimal point to give a number that is at least 1 but less than 10.

Some Powers of 10

Standard Number: 10,000, Multiples of 10: 10×10×10×10, Scientific Notation: $1 \times 10^4$
Standard Number: 1,000, Multiples of 10: 10×10×10, Scientific Notation: $1 \times 10^3$
Standard Number: 100, Multiples of 10: 10×10, Scientific Notation: $1 \times 10^2$
Standard Number: 10, Multiples of 10: 10, Scientific Notation: $1 \times 10^1$
Standard Number: 1, Multiples of 10: 1, Scientific Notation: $1 \times 10^0$
Standard Number: 0.1, Multiples of 10: one tenth, Scientific Notation: $1 \times 10^{-1}$
Standard Number: 0.01, Multiples of 10: one tenth times one tenth equals one hundredth, Scientific Notation: $1 \times 10^{-2}$
Standard Number: 0.001, Multiples of 10: one tenth times one tenth times one tenth equals one thousandth, Scientific Notation: $1 \times 10^{-3}$
Standard Number: 0.0001, Multiples of 10: one tenth times one tenth times one tenth times one tenth equals one ten thousandth, Scientific Notation: $1 \times 10^{-4}$

Some Measurements in Scientific Notation

Volume of gasoline used in the United States each year: Standard Number: 550,000,000,000 Liters, Scientific Notation: $5.5 \times 10^{11}$ liters
Diameter of Earth: Standard Number: 12,800,000 meters, Scientific Notation: $1.28 \times 10^7$ meters
Average volume of blood pumped in 1 day: Standard Number: 8,500 Liters, Scientific Notation: $8.5 \times 10^3$ liters
Time for light to travel from the Sun to Earth: Standard Number: 500 seconds, Scientific Notation: $5 \times 10^2$ seconds
Mass of a typical human: Standard Number: 68 kilograms, Scientific Notation: $6.8 \times 10^1$ kilograms
Mass of stirrup bone in ear: Standard Number: 0.003 gram, Scientific Notation: $3 \times 10^{-3}$ grams
Diameter of a chickenpox (Varicella zoster) virus: Standard Number: 0.000 000 3 meter, Scientific Notation: $3 \times 10^{-7}$ meters
Mass of bacterium (mycoplasma): Standard Number: 0.000 000 000 000 000 000 1 kilogram, Scientific Notation: $1 \times 10^{-19}$ kilograms

Comparing Numbers in Standard and Scientific Notation

Diameter of the Earth:
- Standard Format: 12,800,000 meters
- Scientific Notation: $1.28 \times 10^7$ meters
Mass of a human:
- Standard Format: 68 kilograms
- Scientific Notation: $6.8 \times 10^1$ kilograms
Diameter of a chickenpox virus:
- Standard Format: 0.000 000 3 centimeters
- Scientific Notation: $3 \times 10^{-7}$ centimeters

Scientific Notation and Calculators

You can enter a number written in scientific notation on many calculators using the EE or EXP key.
When a calculator display appears in scientific notation, it is shown as a number between 1 and 10, followed by a space and the power (exponent).
On many scientific calculators, a number is converted to scientific notation, using the appropriate keys.

Learning Check 1: Scientific Notation

Write each of the following in correct scientific notation:
- A. 64 000
- B. 0.021

Solution 1: Scientific Notation

A. 64 000:
- Step 1: Move the decimal point to obtain a coefficient that is at least 1 but less than 10: 6.4
- Step 2: Express the number of places moved as a power of 10: $10^4$
- Step 3: Write the product of the coefficient multiplied by the power of 10: $6.4 \times 10^4$
B. 0.021:
- Step 1: Move the decimal point to obtain a coefficient that is at least 1 but less than 10: 2.1
- Step 2: Express the number of places moved as a power of 10: $10^{-2}$
- Step 3: Write the product of the coefficient multiplied by the power of 10: $2.1 \times 10^{-2}$

Learning Check 2: Scientific Notation Selection

Select the correct scientific notation for each:
- A. 0.000 008 (Move the decimal point 6 places to the right.): $8 \times 10^{-6}$
- B. 72 000 000 (Move the decimal point 7 places to the left.): $7.2 \times 10^7$