Step-by-Step Guidance for ACS General Chemistry Final Exam Practice Questions

Q1. The speed of light is 3.0 \times 10^8 \text{ m/s}. What is this speed in nm/ms?

Background

Topic: Unit Conversions (Dimensional Analysis)

This question tests your ability to convert between different units of measurement, specifically meters to nanometers and seconds to milliseconds.

Key Terms and Formulas:

• 1 meter (m) = $1 \times 10^9$ nanometers (nm)

• 1 second (s) = $1 \times 10^3$ milliseconds (ms)

Step-by-Step Guidance

1. Start with the given value: $3.0 \times 10^8 \ \text{m/s}$.

2. Set up the conversion to nanometers by multiplying by $1 \times 10^9 \ \text{nm}/1 \ \text{m}$.

3. Set up the conversion to milliseconds by dividing by $1 \times 10^3 \ \text{ms}/1 \ \text{s}$ (or multiplying by $1 \ \text{s}/1 \times 10^3 \ \text{ms}$).

4. Combine the conversions into one expression:

5. $3.0 \times 10^8 \ \text{m/s} \times \frac{1 \times 10^9 \ \text{nm}}{1 \ \text{m}} \times \frac{1 \ \text{s}}{1 \times 10^3 \ \text{ms}}$

Try solving on your own before revealing the answer!

Final Answer: 3.0 \times 10^{14} \text{ nm/ms}

After performing the unit conversions, you find that the speed of light is $3.0 \times 10^{14}$ nm/ms.

Q2. The density of helium is 0.164 kg/m^3. What is this density in lb/ft^3? (1 kg = 2.20 lb and 1 m = 3.28 ft)

Background

Topic: Unit Conversions (Density)

This question tests your ability to convert density units from the metric system to the imperial system.

Key Terms and Formulas:

• Density = mass/volume

• 1 kg = 2.20 lb

• 1 m = 3.28 ft, so $1 \text{ m}^3 = (3.28)^3 \text{ ft}^3$

Step-by-Step Guidance

1. Start with the given density: $0.164 \ \text{kg/m}^3$.

2. Convert kilograms to pounds: $0.164 \ \text{kg} \times \frac{2.20 \ \text{lb}}{1 \ \text{kg}}$.

3. Convert cubic meters to cubic feet: $1 \ \text{m}^3 = (3.28)^3 \ \text{ft}^3$.

4. Set up the conversion for volume: $\frac{1}{(3.28)^3} \ \text{m}^3/\text{ft}^3$.

5. Combine the conversions to get the density in lb/ft^3.

Try solving on your own before revealing the answer!

Final Answer: 0.0102 lb/ft^3

After converting both mass and volume units, the density is $0.0102$ lb/ft^3.

Q3. Based on the figure, what volume should be reported for the liquid?

Background

Topic: Significant Figures and Measurement

This question tests your understanding of how to read a measurement from a graduated instrument and report it with the correct number of significant figures.

Key Terms and Concepts:

• Significant figures: The digits in a measurement that are known with certainty plus one estimated digit.

• Graduated cylinder: Always estimate one digit beyond the smallest graduation.

Step-by-Step Guidance

1. Examine the figure and identify the smallest graduation on the measuring device.

2. Read the value at the bottom of the meniscus (for liquids).

3. Estimate one digit beyond the smallest graduation for your measurement.

4. Report the volume with the correct number of significant figures based on your estimation.

Try solving on your own before revealing the answer!

Final Answer: 20.57 mL

The correct answer uses all certain digits plus one estimated digit, reflecting proper use of significant figures.

Q4. What is the correctly reported mass of water based on the data in the table?

Background

Topic: Significant Figures in Subtraction

This question tests your ability to subtract measured values and report the result with the correct number of significant figures.

Key Terms and Concepts:

• Significant figures in subtraction: The answer should have the same number of decimal places as the measurement with the fewest decimal places.

Step-by-Step Guidance

1. Identify the mass of beaker and water: 29.62 g.

2. Identify the mass of beaker only: 28.3220 g.

3. Subtract the mass of the beaker from the total mass to find the mass of water.

4. Determine the number of decimal places in each measurement and report the answer with the correct number of decimal places.

Try solving on your own before revealing the answer!

Final Answer: 1.30 g

The answer is reported with two decimal places, matching the measurement with the fewest decimal places.

Q5. What is the name of Ti3+(PO4)4?

Background

Topic: Nomenclature of Ionic Compounds with Transition Metals

This question tests your ability to name ionic compounds, especially those containing transition metals with variable oxidation states.

Key Terms and Concepts:

• Transition metals: Can have multiple oxidation states, which must be specified in the name.

• Polyatomic ions: PO43- is phosphate.

• Roman numerals: Indicate the charge of the metal cation.

Step-by-Step Guidance

1. Identify the charge on the phosphate ion: $\text{PO}_4^{3-}$.

2. Set up the charge balance for the compound: $\text{Ti}_x(\text{PO}_4)_y$.

3. Calculate the total negative charge from four phosphate ions: $4 \times (-3) = -12$.

4. Determine the charge on each titanium ion so that the total positive charge balances the total negative charge.

5. Assign the correct Roman numeral to titanium based on its oxidation state.

Try solving on your own before revealing the answer!

Final Answer: Titanium (IV) phosphate

The correct name includes the Roman numeral IV to indicate the +4 oxidation state of titanium.