CHEM1111 Exam 01 Review – Step-by-Step Study Guidance

Q1. What is the difference between precision and accuracy?

Background

Topic: Measurement in Chemistry

This question tests your understanding of two important concepts in scientific measurement: precision and accuracy. These terms describe the quality of measurements and are fundamental in laboratory work.

Key Terms:

• Precision: How close repeated measurements are to each other.

• Accuracy: How close a measurement is to the true or accepted value.

Step-by-Step Guidance

1. Think about a scenario where you measure the same quantity multiple times. Are your results similar to each other? This relates to precision.

2. Now, consider whether your measurements are close to the actual or accepted value. This relates to accuracy.

3. Try to come up with your own examples (e.g., hitting a target with darts) to distinguish between these two concepts.

Try explaining the difference in your own words before checking the answer!

Final Answer:

Precision is the agreement between measured values (how close the measurements are to each other), while accuracy is the agreement between measured values and the actual value (how close the measurements are to the true value).

Q2. How many significant figures are in the following numbers: a) 37.8, b) 10.1, c) 0.00053, d) 5.300, e) 3600, f) 3.600 x 103?

Background

Topic: Significant Figures

This question tests your ability to identify the number of significant figures in various numbers, which is important for reporting measurements correctly in chemistry.

Key Terms:

• Significant Figures: The digits in a number that carry meaning contributing to its precision.

Rules for Significant Figures:

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros are significant only if there is a decimal point.

Step-by-Step Guidance

1. For each number, identify which digits are significant based on the rules above.

2. For numbers with zeros, pay attention to their position (leading, captive, or trailing).

3. For numbers in scientific notation, all digits in the coefficient are significant.

4. For ambiguous cases (like 3600), consider if a decimal point is present or if scientific notation is used to clarify.

Try counting the significant figures for each number before checking the answer!

Final Answer:

a) 37.8 – three; b) 10.1 – three; c) 0.00053 – two; d) 5.300 – four; e) 3600 – ambiguous (could be two, three, or four); f) 3.600 x 103 – four.

Q3. How many inches are there in a kilometer?

Background

Topic: Unit Conversions

This question tests your ability to convert between metric and imperial units using dimensional analysis.

Key Conversion Factors:

• 1 km = 1000 m

• 1 m = 100 cm

• 1 in = 2.54 cm

Step-by-Step Guidance

1. Start with 1 kilometer and set up a chain of conversion factors to cancel out units until you reach inches.

2. Multiply by each conversion factor, making sure units cancel appropriately at each step.

3. Write out the full expression before calculating.

4. Check that all units except inches cancel out.

Try setting up the conversion before checking the answer!

Final Answer:

1 km × (1000 m / 1 km) × (100 cm / 1 m) × (1 in / 2.54 cm) = 39,370 in

Q4. One yard is 36 inches. One inch is 2.54 cm. How many cubic yards are there in a cubic meter?

Background

Topic: Volume Unit Conversions

This question tests your ability to convert between metric and imperial units for volume, using dimensional analysis and cubic conversion factors.

Key Conversion Factors:

• 1 m = 100 cm

• 1 in = 2.54 cm

• 1 foot = 12 in

• 1 yard = 3 feet

Step-by-Step Guidance

1. Remember that when converting cubic units, you must cube each conversion factor (e.g., $(1 \text{ m} = 100 \text{ cm})^3$).

2. Set up the conversion starting with $1 \text{ m}^3$ and multiply by each conversion factor cubed.

3. Write out the full chain of conversions, making sure units cancel at each step.

4. Check that all units except cubic yards cancel out.

Try writing out the conversion chain before checking the answer!

Final Answer:

1 m3 × (100 cm / 1 m)3 × (1 in / 2.54 cm)3 × (1 foot / 12 in)3 × (1 yard / 3 foot)3 = 1.31 yard3

Q5. Granite has a density of 2.6 g/cm3. If a block of granite weighs 52 g, what is its volume in cm3?

Background

Topic: Density Calculations

This question tests your ability to use the density formula to solve for volume.

Key Formula:

$D = \frac{m}{v}$

Where:

• $D$ = density (g/cm3)

• $m$ = mass (g)

• $v$ = volume (cm3)

Step-by-Step Guidance

1. Write the density formula: $D = \frac{m}{v}$

2. Rearrange to solve for volume: $v = \frac{m}{D}$

3. Identify the given values: $m = 52 \text{ g}$, $D = 2.6 \text{ g/cm}^3$

4. Plug the values into the rearranged formula, but do not calculate yet.

Try plugging in the values and see what you get before checking the answer!

Final Answer:

$v = \frac{52}{2.6} = 20 \text{ cm}^3$

Q6. Room temperature is 23 °C. a) Convert this to Kelvin. b) Convert this to Fahrenheit.

Background

Topic: Temperature Conversions

This question tests your ability to convert between Celsius, Kelvin, and Fahrenheit temperature scales.

Key Formulas:

• Kelvin: $K = ^\circ C + 273.15$

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

Step-by-Step Guidance

1. For part (a), add 273.15 to the Celsius temperature to get Kelvin.

2. For part (b), multiply the Celsius temperature by 9/5, then add 32 to get Fahrenheit.

3. Write out the setup for each calculation before solving.

Try setting up the calculations before checking the answer!

Final Answer:

23 °C = 296 K or 73.4 °F