Introduction to Chemistry

Ch. 1

What Is Chemistry?◦ Why is the scope of chemistry so vast?

What Is Chemistry?1.1

Matter is anything that has mass and occupies space.

Chemistry is the study of the composition of matter and the changes that matter undergoes.

What Is Chemistry?1.1

◦ Because living and nonliving things are made of matter, chemistry affects all aspects of life and most natural events.

What Is Chemistry?1.1

Alchemy

Alchemy◦ How did alchemy lay the groundwork for

chemistry?

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Alchemy

◦ Alchemists developed the tools and techniques for working with chemicals.

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Alchemy

Alchemists developed processes for separating mixtures and purifying chemicals. They designed equipment that is still in use today including beakers, flasks, tongs, funnels, and the mortar and pestle.

Mortar and Pestle

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The Scientific Method The Scientific Method

◦ What are the steps in the scientific method?

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The Scientific Method The scientific method is a logical, systematic

approach to the solution of a scientific problem.

Steps in the scientific method include making observations, testing hypotheses, and developing theories.

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Observations Use one or more of the 5 senses to gather

information A noting and recording of…. FACTS!!!

◦ Example: There are 23 desks in the room.

Inferences Logical interpretation based upon prior

knowledge and experience Based upon observations

◦ Example: When you entered the room, you most likely inferred that the individual in the front of the room is the teacher.

Note the differences In laboratory exercises, record observations NOT

inferences Inferences may be used when writing the

conclusion to your lab.

Let’s test your observation skills…◦ You’ll need a piece of paper and a writing

utensil

Answer these questions

1. What animals are crossing the road?2. How many pedestrians are in the crosswalk?3. Is there a manhole in the street?4. What are the pedestrians wearing on their feet?5. Are all pedestrians in the crosswalk wearing

hats?6. How many American flags are flying?7. Is the traffic light red, green or yellow?8. What city is this?

Observation vs. Inference On the next slide, state whether the statement is

an observation or an inference.

1. There is a representation of a face on one side of the coin.

2. The Latin word "Dei" means "God."3. The coin was made by deeply religious people.4. The date 1722 is printed on one side of the coin.5. The coin was made in 1722.6. The face on the coin is a representation of the

nation's president.

Types of Observations Qualitative observations –

◦ Descriptive; do not involve measurement◦ Color, texture, smell, taste

Quantitative observations – ◦ Measurements or counted quantities◦ Mass, volume, temperature, density◦ There are 18 students in the room

Most experiments involve both types of observations.

Observe for one minute and record qualitative observations…

Types of Observations

The Scientific Method◦ Testing Hypotheses

An hypothesis is a proposed explanation for an observed set of facts.

You make daily hypotheses: You observe that your flashlight won’t work. You guess

the flashlight needs new batteries so you test your hypothesis by putting new batteries in the flashlight.

What is another example?

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The Scientific Method An experiment is a procedure that is used to test a

hypothesis. When you design experiments, you deal with variables, or factors that can change. The variable that you change during an experiment is

the manipulated variable, or independent variable. The variable that is observed during the experiment is

the responding variable, or dependent variable. When graphing data, the independent variable goes on

the X axis and the dependent on the Y axis. An experiment was done to determine the effect of pH on

the rate of a chemical reaction. Which variable goes on the x axis and which on the y?

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The Scientific Method◦ Developing Theories

Once a hypothesis meets the test of repeated experimentation, it may become a theory. A theory is a well-tested explanation for a broad set of

observations. A theory may need to be changed at some point in the

future to explain new observations or experimental results. Atomic theory states that the atom is composed of a

positive nucleus surrounded by a negative electron cloud.

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The Scientific Method◦ Scientific Laws

A scientific law is a concise statement that summarizes the results of many observations and experiments.

A scientific law doesn’t try to explain the relationship it describes. That explanation requires a theory. The law of conservation of matter states that matter is

neither created nor destroyed during a chemical reaction.

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Steps in the Scientific MethodThe Scientific Method