Introduction to Chemistry Exam 1 Review – Step-by-Step Study Guidance

Q1. Which of the following items does NOT contain chemicals?

Background

Topic: Chemistry in Everyday Life

This question tests your understanding of what is considered a "chemical" and challenges common misconceptions about chemicals in everyday items.

Key Terms:

• Chemical: Any substance with a definite composition; all matter is made of chemicals.

Step-by-Step Guidance

1. Review the definition of a chemical. Remember, a chemical is any substance consisting of matter, including solids, liquids, and gases.

2. Consider each option: drain cleaner, organically grown vegetables, air, and insecticides. Think about whether each is made of matter and has a definite composition.

3. Ask yourself: Is there anything in the list that is not made of chemicals, or is everything composed of chemicals?

Try solving on your own before revealing the answer!

Final Answer: E) All of the above contain chemicals.

Everything listed is made of chemicals, including air and organically grown vegetables. All matter is composed of chemicals.

Q2. Which statement about a hypothesis is TRUE?

Background

Topic: Scientific Method

This question tests your understanding of the definition and characteristics of a hypothesis in science.

Key Terms:

• Hypothesis: A tentative explanation or prediction that can be tested by experiments.

• Scientific Method: A systematic approach to research and experimentation.

Step-by-Step Guidance

1. Recall the definition of a hypothesis and its role in the scientific method.

2. Review each statement: Is a hypothesis testable? Can it be proven wrong? Is it part of the scientific method?

3. Determine if more than one statement is correct, or if all are true.

Try solving on your own before revealing the answer!

Final Answer: E) All of the above statements are true.

A hypothesis is a tentative explanation, can be tested, may be proven wrong, and is part of the scientific method.

Q3. What term best describes a brief statement that summarizes many past observations and predicts new ones?

Background

Topic: Scientific Laws and Theories

This question tests your ability to distinguish between scientific laws, theories, hypotheses, and experiments.

Key Terms:

• Scientific Law: A concise statement that summarizes a wide range of observations and predicts future events.

• Theory: A well-substantiated explanation of some aspect of the natural world.

Step-by-Step Guidance

1. Review the definitions of experiment, hypothesis, scientific law, and theory.

2. Focus on the phrase "summarizes many past observations and predicts new ones." Which term fits this description?

3. Eliminate options that do not match the definition provided in the question.

Try solving on your own before revealing the answer!

Final Answer: C) scientific law

A scientific law summarizes observations and predicts new ones, but does not explain why.

Q4. Which of the following is an example of an observation?

Background

Topic: Scientific Method – Observations vs. Explanations

This question tests your ability to distinguish between observations (what is seen or measured) and explanations or theories.

Key Terms:

• Observation: Information gathered using the senses or instruments, without interpretation.

Step-by-Step Guidance

1. Review the difference between an observation (what you see, hear, or measure) and an explanation (why something happens).

2. Read each option and decide if it describes something directly observed or an interpretation/explanation.

3. Identify the option that is a direct sensory experience or measurement.

Try solving on your own before revealing the answer!

Final Answer: C) When a can of soda pop is opened, a fizzing sound is heard.

This is a direct observation, not an explanation or theory.

Q5. A sample of wood with a mass of 3.0 grams was burned in an open dish. The ashes weighed 1.2 grams. What happened to the rest of the wood?

Background

Topic: Law of Conservation of Mass

This question tests your understanding of what happens to matter during a chemical reaction, specifically combustion.

Key Terms:

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.

• Combustion: A chemical reaction with oxygen that produces heat, light, and new substances (often gases).

Step-by-Step Guidance

1. Calculate the difference in mass: $3.0 \text{ g} - 1.2 \text{ g}$.

2. Think about what happens during burning: does all the wood become ash, or are some products released as gases?

3. Recall the law of conservation of mass and consider where the missing mass could have gone.

Try solving on your own before revealing the answer!

Final Answer: B) The remaining 1.8 grams was converted into gaseous compounds.

During combustion, gases like CO2 and H2O are released and escape into the air, accounting for the missing mass.

Q6. Charcoal was burned in a barbecue grill. The ashes that remained weighed considerably less than the charcoal that was burned. Does this mean that the law of conservation of mass is wrong? Explain.

Background

Topic: Law of Conservation of Mass

This question asks you to apply the law of conservation of mass to a real-world scenario and explain apparent discrepancies.

Key Terms:

• Law of Conservation of Mass: The total mass of reactants equals the total mass of products in a chemical reaction.

• Combustion: Burning, which produces gases as well as solids.

Step-by-Step Guidance

1. Recall what happens during combustion: solid charcoal reacts with oxygen to form gases and ash.

2. Consider whether all products (solids and gases) are collected and weighed after burning.

3. Think about why the mass of the ashes is less than the original charcoal and what happens to the rest of the mass.

Try solving on your own before revealing the answer!

Final Answer: No, the law of conservation of mass is not wrong.

The missing mass is due to gaseous products (like CO2 and H2O) escaping into the air. If all products were collected, the total mass would be the same as the starting charcoal.