Q1. Write these numbers in scientific notation:

• a. 12,300,000

• b. 0.0000405

Background

Topic: Scientific Notation

This question tests your ability to express numbers in scientific notation, which is a way to write very large or very small numbers using powers of ten.

Key Terms:

• Scientific notation: A number written as , where and is an integer.

Step-by-Step Guidance

1. For each number, identify the decimal point's new position so that only one nonzero digit remains to its left.

2. Count how many places the decimal point moves. This determines the exponent for .

3. If the decimal moves to the left (for large numbers), is positive. If it moves to the right (for small numbers), $n$ is negative.

4. Write the number in the form .

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Q2. Convert these measurements:

• a. 0.80 km = ______ m

• b. 1.30 L = ______ mL

• c. 10 kg = ______ lb

Background

Topic: Unit Conversion

This question tests your ability to convert between metric units and between metric and English units using conversion factors.

Key Terms and Conversion Factors:

• 1 km = 1000 m

• 1 L = 1000 mL

• 1 kg = 2.2046 lb

Step-by-Step Guidance

1. For each conversion, write the original value and multiply by the appropriate conversion factor.

2. Set up the conversion so that units cancel, leaving the desired unit.

3. For example, to convert km to m:

4. Repeat for the other conversions, but stop before calculating the final value.

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Q3. A block of ice measures 15 cm x 15 cm x 15 cm. What should be the mass of the ice in grams? (The density of ice = 0.917 g/cm3)

Background

Topic: Density Calculations

This question tests your ability to use the density formula to find mass, given volume and density.

Key Formula:

Rearranged:

Step-by-Step Guidance

1. Calculate the volume of the block:

2. Multiply the calculated volume by the density:

3. Set up the multiplication, but stop before computing the final mass.

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Q4. Are the following changes chemical changes or physical changes?

• a. Water evaporates from an open container.

• b. A match is burned.

• c. Sugar is dissolved in coffee.

Background

Topic: Chemical vs. Physical Changes

This question tests your understanding of the difference between physical changes (changes in state or appearance) and chemical changes (changes in composition).

Key Terms:

• Physical change: A change that does not alter the chemical composition.

• Chemical change: A change that results in the formation of new substances.

Step-by-Step Guidance

1. For each example, ask: Does the substance's chemical identity change?

2. Consider whether new substances are formed or if only the state/appearance changes.

3. Classify each change as physical or chemical, but stop before stating the classification.

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Q5. Classify the following as an element, a compound, or a mixture:

• a. Oxygen gas

• b. Milk

• c. Distilled water

Background

Topic: Classification of Matter

This question tests your ability to distinguish between elements, compounds, and mixtures based on their composition.

Key Terms:

• Element: A pure substance made of only one kind of atom.

• Compound: A pure substance made of two or more elements chemically combined.

• Mixture: A combination of two or more substances not chemically combined.

Step-by-Step Guidance

1. For each substance, determine if it is made of only one type of atom, two or more types chemically bonded, or a physical blend.

2. Use definitions to classify each, but stop before stating the classification.

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Q6. State the law of:

• a. Conservation of mass

• b. Definite proportions

• c. Multiple proportions

Background

Topic: Fundamental Laws of Chemistry

This question tests your knowledge of three foundational laws that govern chemical reactions and compounds.

Key Terms:

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

• Law of definite proportions: A chemical compound always contains the same elements in the same proportion by mass.

• Law of multiple proportions: When two elements form more than one compound, the ratios of the masses of the second element that combine with a fixed mass of the first element are simple whole numbers.

Step-by-Step Guidance

1. Recall the definition of each law.

2. Write a brief statement for each law, but stop before writing the full statement.

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Q7. Which of the above laws are illustrated by the following?

• a. Heptane is always composed of 84% carbon and 16% hydrogen.

• b. Carbon and oxygen can combine to make either CO2 or CO.

• c. 2 grams of hydrogen will combine with 16 grams of oxygen to make 18 grams of water.

Background

Topic: Application of Chemical Laws

This question tests your ability to match real-world examples to the correct chemical law.

Key Terms:

• Refer to the definitions from Q6.

Step-by-Step Guidance

1. For each example, identify which law is being demonstrated based on the description.

2. Match the example to the law, but stop before stating the match.

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Q8. When 18.0 grams of water is decomposed by electrolysis, 16.0 g of O and 2.0 g of H are produced. How much hydrogen should be produced by the electrolysis of 54 g of water?

Background

Topic: Conservation of Mass and Proportional Reasoning

This question tests your ability to use mass ratios and proportional reasoning to predict the outcome of a chemical reaction.

Key Formula:

Set up a proportion based on the known decomposition:

Step-by-Step Guidance

1. Write the ratio of hydrogen produced to water decomposed from the given data.

2. Set up a proportion to solve for the unknown mass of hydrogen () when 54 g of water is decomposed.

3. Cross-multiply and solve for , but stop before calculating the final value.

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Q9. Several researchers contributed to our model of the atom. Match each with their discovery:

• a. The mass of an atom is concentrated in the nucleus.

• b. The electron is negatively charged.

• c. X-rays

• d. The mass of an electron.

1. J J Thompson

2. Rutherford

3. Millikan

4. Bequerel

Background

Topic: Atomic Theory and Historical Discoveries

This question tests your knowledge of key scientists and their contributions to atomic theory.

Key Terms:

• Know which scientist is associated with each discovery.

Step-by-Step Guidance

1. Recall the main discovery or experiment for each scientist.

2. Match each discovery to the correct scientist, but stop before stating the match.

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Q10. Describe each of the following and tell whether it is located inside or outside the nucleus of the atom:

• a. Proton

• b. Electron

• c. Neutron

Background

Topic: Structure of the Atom

This question tests your understanding of the basic subatomic particles and their location within the atom.

Key Terms:

• Proton: Positively charged particle

• Electron: Negatively charged particle

• Neutron: Neutral particle

Step-by-Step Guidance

1. Describe the charge and mass of each particle.

2. State whether each is found inside or outside the nucleus, but stop before stating the location.

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Q11. How many protons and neutrons do each of the following have?

• a. Phosphorus-31

• b. Radon-222

Background

Topic: Isotopes and Atomic Structure

This question tests your ability to determine the number of protons and neutrons in an isotope based on its atomic number and mass number.

Key Formula:

Step-by-Step Guidance

1. Find the atomic number for each element (from the periodic table).

2. Subtract the atomic number from the mass number to find the number of neutrons.

3. Write the number of protons and neutrons for each, but stop before stating the numbers.

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Q12. How many electrons does a magnesium atom have? Write out the electron configuration of magnesium.

Background

Topic: Electron Configuration

This question tests your ability to determine the number of electrons in a neutral atom and write its electron configuration.

Key Terms:

• Atomic number: Number of protons (and electrons in a neutral atom)

• Electron configuration: The arrangement of electrons in shells/subshells

Step-by-Step Guidance

1. Find the atomic number of magnesium (from the periodic table).

2. Write the electron configuration using the Aufbau principle, filling subshells in order.

3. Stop before writing the full configuration.

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Q13. The elements of the oxygen group (Group 16) have similar chemical properties. What do their electron configurations have in common?

Background

Topic: Periodic Table and Electron Configuration

This question tests your understanding of how elements in the same group have similar valence electron configurations, leading to similar chemical properties.

Key Terms:

• Valence electrons: Electrons in the outermost shell

• Group 16: Oxygen, sulfur, selenium, etc.

Step-by-Step Guidance

1. Look at the electron configuration for each Group 16 element.

2. Identify the number of valence electrons and the pattern in their outermost shell.

3. Stop before stating the commonality.

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