Intro to Chemistry Exam 1 Study Guide – Step-by-Step Guidance

Q1. Identify whether the following substances are elements or compounds:

• Sodium (Na)

• Water (H₂O)

• Oxygen (O₂)

• Table Salt (NaCl)

Background

Topic: Elements and Compounds

This question tests your understanding of the difference between elements (pure substances made of only one type of atom) and compounds (substances made from two or more different elements chemically bonded together).

Key Terms:

• Element: A pure substance consisting of only one type of atom.

• Compound: A substance formed when two or more elements are chemically bonded together.

Step-by-Step Guidance

1. Look at the chemical formula for each substance. If it contains only one type of atom (e.g., Na or O₂), it is an element. If it contains more than one type of atom (e.g., H₂O or NaCl), it is a compound.

2. For each substance, identify the types of atoms present. For example, Na contains only sodium atoms, while H₂O contains both hydrogen and oxygen atoms.

3. Decide if the substance is an element or a compound based on your analysis in the previous step.

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Q2. How many protons, neutrons, and electrons are in an atom of Carbon-14 (¹⁴C)?

Background

Topic: Atomic Structure

This question tests your ability to determine the number of protons, neutrons, and electrons in an atom, given its atomic number and mass number.

Key Terms and Formulas:

• Atomic Number (Z): Number of protons in the nucleus of an atom.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

• Number of Neutrons: $\text{Neutrons} = A - Z$

• Number of Electrons: In a neutral atom, electrons = protons.

Step-by-Step Guidance

1. Identify the atomic number (Z) for carbon. This tells you the number of protons.

2. Use the mass number (A) given (14 for Carbon-14) and subtract the atomic number to find the number of neutrons: $\text{Neutrons} = A - Z$.

3. For a neutral atom, the number of electrons equals the number of protons.

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Q3. Is burning a piece of wood a physical or chemical change?

Background

Topic: Physical vs. Chemical Changes

This question tests your ability to distinguish between physical changes (which do not alter the chemical composition) and chemical changes (which result in new substances).

Key Terms:

• Physical Change: A change that affects the form of a substance, but not its chemical composition.

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

Step-by-Step Guidance

1. Consider what happens when wood burns: are new substances formed, or is it just a change in state or appearance?

2. Think about the evidence of chemical changes (e.g., color change, gas production, formation of new substances).

3. Decide if burning wood fits the criteria for a physical or chemical change.

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Q4. Calculate the average atomic mass of chlorine given two isotopes: chlorine-35 (mass = 34.969 amu, abundance = 75.77%) and chlorine-37 (mass = 36.966 amu, abundance = 24.23%).

Background

Topic: Isotopes and Atomic Mass Calculation

This question tests your ability to calculate the weighted average atomic mass of an element based on the masses and abundances of its isotopes.

Key Formula:

$\text{Average atomic mass} = (\text{mass}_1 \times \text{abundance}_1) + (\text{mass}_2 \times \text{abundance}_2)$

Step-by-Step Guidance

1. Convert the percent abundances to decimal form by dividing by 100.

2. Multiply the mass of each isotope by its decimal abundance.

3. Add the results from each isotope to find the average atomic mass.

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Q5. A piece of metal has a mass of 50 grams and a volume of 20 cm³. What is the density of the metal?

Background

Topic: Density and Mass Calculations

This question tests your ability to use the density formula to solve for density when given mass and volume.

Key Formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Step-by-Step Guidance

1. Write down the given values: mass = 50 g, volume = 20 cm³.

2. Plug these values into the density formula: $\text{Density} = \frac{50\ \text{g}}{20\ \text{cm}^3}$

3. Set up the division, but do not calculate the final value yet.

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Q6. How many significant figures are in the number 0.004560?

Background

Topic: SI Units and Significant Figures

This question tests your understanding of how to count significant figures in a given number.

Key Terms:

• Significant Figures: All nonzero digits, zeros between nonzero digits, and trailing zeros after a decimal point are significant.

Step-by-Step Guidance

1. Identify and ignore leading zeros (zeros before the first nonzero digit).

2. Count all nonzero digits, zeros between nonzero digits, and any trailing zeros after the decimal point.

3. Sum up the total number of significant figures.

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Q7. What type of property is color: physical or chemical?

Background

Topic: Properties of Matter

This question tests your ability to distinguish between physical and chemical properties.

Key Terms:

• Physical Property: Can be observed or measured without changing the substance's chemical identity.

• Chemical Property: Describes a substance's ability to undergo a specific chemical change.

Step-by-Step Guidance

1. Ask yourself if observing color changes the chemical composition of the substance.

2. Decide if color is a physical or chemical property based on your reasoning.

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Q8. Is the melting of ice an endothermic or exothermic reaction?

Background

Topic: Endothermic vs. Exothermic Reactions

This question tests your understanding of energy changes during physical and chemical processes.

Key Terms:

• Endothermic: A process that absorbs heat from the surroundings.

• Exothermic: A process that releases heat to the surroundings.

Step-by-Step Guidance

1. Think about whether heat is absorbed or released when ice melts.

2. Recall the definitions of endothermic and exothermic processes.

3. Decide which term applies to the melting of ice.

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Q9. What is the correct name for the compound Na₂O?

Background

Topic: Chemical Nomenclature

This question tests your ability to name ionic compounds, specifically those containing a group 1 metal and a nonmetal.

Key Terms:

• Ionic Compound: Formed from a metal and a nonmetal.

• Naming Rule: Name the metal first, then the nonmetal with its ending changed to "-ide." Do not use prefixes for ionic compounds.

Step-by-Step Guidance

1. Identify the cation (metal) and anion (nonmetal) in the formula.

2. Name the metal (Na) as sodium.

3. Name the nonmetal (O) as oxide.

4. Combine the names to form the compound's name.

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Q10. What is the correct name for the compound CuS?

Background

Topic: Chemical Nomenclature

This question tests your ability to name ionic compounds containing transition metals, which may have more than one possible charge.

Key Terms:

• Transition Metal: May have multiple possible charges; indicate the charge with a Roman numeral in parentheses.

• Naming Rule: Name the metal with its charge, then the nonmetal with its ending changed to "-ide."

Step-by-Step Guidance

1. Identify the cation (Cu) and anion (S).

2. Determine the charge on the copper ion based on the formula.

3. Name the metal (copper) with its charge in Roman numerals.

4. Name the nonmetal (sulfur) as sulfide.

5. Combine the names to form the compound's name.

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Q11. What is the correct name for the compound P₂O₅?

Background

Topic: Chemical Nomenclature (Molecular Compounds)

This question tests your ability to name molecular (covalent) compounds using prefixes to indicate the number of atoms.

Key Terms:

• Molecular Compound: Formed from two nonmetals.

• Naming Rule: Use prefixes (di-, tri-, tetra-, penta-, etc.) to indicate the number of each atom. The second element ends with "-ide."

Step-by-Step Guidance

1. Identify the number of phosphorus and oxygen atoms in the formula.

2. Apply the appropriate prefixes: "di-" for two phosphorus, "penta-" for five oxygen.

3. Name the compound by combining the prefixes and element names, ending with "-ide" for oxygen.

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Q12. Convert 25°C to Fahrenheit.

Background

Topic: Temperature Conversions

This question tests your ability to convert temperatures between Celsius and Fahrenheit using the appropriate formula.

Key Formula:

$^\circ F = (^\circ C \times \frac{9}{5}) + 32$

Step-by-Step Guidance

1. Write down the given temperature in Celsius: 25°C.

2. Multiply the Celsius temperature by $\frac{9}{5}$.

3. Add 32 to the result from the previous step to get the temperature in Fahrenheit.

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Q13. If the density of a substance is 3.2 g/cm³ and its volume is 50 cm³, what is the mass of the substance?

Background

Topic: Density Calculations

This question tests your ability to rearrange the density formula to solve for mass.

Key Formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Rearranged: $\text{Mass} = \text{Density} \times \text{Volume}$

Step-by-Step Guidance

1. Write down the given values: density = 3.2 g/cm³, volume = 50 cm³.

2. Plug these values into the rearranged formula: $\text{Mass} = 3.2\ \text{g/cm}^3 \times 50\ \text{cm}^3$

3. Set up the multiplication, but do not calculate the final value yet.

Try solving on your own before revealing the answer!