Chapter 1 Chemistry in Our Lives Karen C. Timberlake

What is Chemistry? Chemistry is the study of composition, structure, properties, and reactions of matter. happens all around you every day. Antacid tablets undergo a chemical reaction when dropped in water.

Chemistry and Matter Matter is another word for all substances that make up our world. Antacid tablets are matter. Water is matter. Glass is matter. Air is matter.

Chemicals Chemicals are substances that have the same composition and properties wherever found. often substances made by chemists that you use every day. Toothpaste is a combination of many chemicals.

Chemicals in the Kitchen

The Scientific Method The scientific method is a set of general principles that helps to describe how a scientist thinks. 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 may be true or false.

Using the Scientific Method Suppose you visit a friend in her home and soon after you arrive, you begin to sneeze. You observe that your friend has a new cat. You ask yourself why you are sneezing and form a hypothesis that you are allergic to cats. You perform experiments to test your hypothesis by visiting other friends with cats. If you sneeze after leaving the other homes with cats, you come to the conclusion that your hypothesis is correct.

Using the Scientific Method The scientific method develops conclusions using observations, hypotheses, and experiments. The hypothesis is modified if the results of the experiments do not support it.

Study Check Identify each of the following as an observation (O), a hypothesis (H), an experiment (E), or a conclusion (C): A. During your visit to the gym, your trainer records that you ran for 25 minutes on the treadmill. B. Scientific studies show that exercising lowers blood pressure. C. Your doctor thinks that your weight loss is due to increased exercise.

Solution Identify each of the following as an observation (O), a hypothesis (H), an experiment (E), or a conclusion (C): A. During your visit to the gym, your trainer records that you ran for 25 minutes on the treadmill. Observation (O) B. Scientific studies show that exercising lowers blood pressure. Conclusion (C) C. Your doctor thinks that your weight loss is due to increased exercise. Hypothesis (H)

E. Interpreting Graphs A graph represents the relationship between two variables. has a horizontal axis, or x axis. has a vertical axis, or y axis.

1.4 Key Math Skills for Chemistry A graph represents the relationship between two variables.

Interpreting Graphs The line on the graph indicates a direct relationship: that the volume of a gas in a balloon increases with increasing temperature. can be used to determine the gas volume at various temperatures.

A. Identifying Place Values For any number, we can identify the place value for each of the digits in that number. The place values for two numbers are listed below: A premature baby has a mass of 2518 grams. A silver coin has a mass of 6.407 grams.

B. Using Positive and Negative Numbers in Calculations 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. A negative number is any number that is less than zero and is written with a negative sign (−).

Multiplication and Division: Positive and Negative Numbers 1. When two positive numbers or two negative numbers are multiplied or divided, the answer is positive (+). 2. When a positive number and a negative number are multiplied or divided, the answer is negative (−).

Addition: Positive and Negative Numbers 1. When two positive numbers are added, the answer is positive. 2. When two negative numbers are added, the answer is negative. 3. When a positive number and a negative number are added, the smaller number is subtracted from the larger number and the result has the same sign as the larger number.

Subtraction: Positive and Negative Numbers When two numbers are subtracted, change the sign of the number to be subtracted and then follow the rules for addition.

C. Calculating Percentages To determine a percentage, divide the parts by the total (whole) and multiply by 100%. If the percentage of red balls is 5, it means there are 5 red balls in every 100 balls.

D. Solving Equations Equations can be rearranged to solve for an unknown variable. 1. Place all like items on one side. 2. Isolate the variable you need to solve for. 3. Check your answer.

Study Check Solve the following equation for P1.

Solution Solve the following equation for P1. To solve for P1, divide both sides by V1.

F. Scientific Notation People have an average of 1 × 105 hairs on the scalp. Each hair is about 8 × 10−6 m wide.

Scientific Notation Numbers written in scientific notation have two parts: Coefficient Power of 10 To write 2400 in the correct scientific notation, the coefficient is 2.4. the power of 10 is 3. write the product of the coefficient multiplied by a power of 10. 2.4 × 103

Scientific Notation 2 400 = 2.4 × 1 000 = 2.4 × 103  3 places Coefficient × Power of 10 0.00086 = = 8.6 × 10−4 4 places  Coefficient × Power of 10

Some Positive Powers of 10

Some Negative Powers of 10

Measurements in Scientific Notation Diameter of chickenpox virus = 0.000 000 3 m = 3 × 10−7 m

Some Measurements Written in Scientific Notation

Scientific Notation and Calculators Numbers in scientific notation can be entered into a calculator using the EXP or EE key. The calculator display shows a number between 1 and 10 followed by a space and the power of 10.

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

Solution Write each of the following in correct scientific notation: A. 64 000 STEP 1 Move the decimal point to obtain a single digit to the left of the decimal 6.4 STEP 2 Count the number of places “moved” that is the power of 10 104 STEP 3 Write the number multiplied by the power of 10. 6.4 × 104

Solution Write each of the following in correct scientific notation: B. 0.021 STEP 1 Move the decimal point to obtain a single digit to the left of the decimal. 2.1 STEP 2 Count the number of places “moved” that is the power of 10. 10−2 STEP 3 Write the number multiplied by the power of 10. 2.1 × 10−2