뒤로General Chemistry: Measurements, Concepts, and Atomic Theory Study Guide
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Q1. What are the basic units for mass, length, and volume?
Background
Topic: SI Units and Measurement
This question tests your knowledge of the fundamental units used in the metric (SI) system for measuring mass, length, and volume, which are foundational in chemistry.
Key Terms
SI Units: The International System of Units used in science.
Mass: The amount of matter in an object.
Length: The measurement of distance.
Volume: The amount of space an object occupies.
Step-by-Step Guidance
Recall the SI base unit for mass. Think about what is used in laboratory balances.
Identify the SI base unit for length, commonly used for measuring distances or dimensions.
Determine the SI derived unit for volume, which is based on the unit for length.
Try solving on your own before revealing the answer!
Final Answer:
Mass: kilogram (kg)
Length: meter (m)
Volume: cubic meter (m3), but liter (L) is commonly used in chemistry
These are the standard SI units for these measurements in chemistry.
Q2. What are the metric prefixes and their mathematical values?
Background
Topic: Metric System Prefixes
This question tests your ability to recall and use the prefixes that modify SI units to represent different orders of magnitude.
Key Terms
Prefix: A word or letter placed before a unit to indicate a multiple or fraction of that unit.
Examples: kilo-, centi-, milli-, micro-, etc.
Step-by-Step Guidance
List the most common metric prefixes used in chemistry, both larger and smaller than the base unit.
For each prefix, recall its symbol and the power of ten it represents.
Organize them from largest to smallest (e.g., kilo- to nano-).
Try solving on your own before revealing the answer!
Final Answer:
kilo- (k): $10^3$
deci- (d): $10^{-1}$
centi- (c): $10^{-2}$
milli- (m): $10^{-3}$
micro- (\mu): $10^{-6}$
nano- (n): $10^{-9}$
These prefixes are used to express multiples or fractions of SI units.
Q3. Why can volume be expressed in cm3? What is cm3 equal to in liters?
Background
Topic: Units of Volume
This question tests your understanding of how volume units are derived from length units and how to convert between cubic centimeters and liters.
Key Terms and Formulas
Volume: $\text{Volume} = \text{length} \times \text{width} \times \text{height}$
1 cm3 = 1 mL
1 L = 1000 mL
Step-by-Step Guidance
Recall that volume is calculated by cubing a length unit (e.g., cm).
Recognize that 1 cm3 is the same as 1 milliliter (mL).
Use the relationship between milliliters and liters to convert cm3 to liters.
Try solving on your own before revealing the answer!
Final Answer:
Volume can be expressed in cm3 because it is a derived unit from length (cm). 1 cm3 = 1 mL, and 1000 cm3 = 1 L.
Q4. Define: Precision, Accuracy, Systematic error, Random error, Significant figures
Background
Topic: Measurement and Error Analysis
This question tests your understanding of key terms related to the quality and reliability of measurements in chemistry.
Key Terms
Precision
Accuracy
Systematic error
Random error
Significant figures
Step-by-Step Guidance
Define precision as it relates to repeated measurements.
Define accuracy in terms of closeness to the true value.
Explain what systematic error is and how it affects results.
Describe random error and its impact on measurements.
Define significant figures and their importance in reporting data.
Try solving on your own before revealing the answer!
Final Answer:
Precision: How close repeated measurements are to each other.
Accuracy: How close a measurement is to the true or accepted value.
Systematic error: Consistent, repeatable error due to faulty equipment or bias.
Random error: Error that varies unpredictably from one measurement to another.
Significant figures: The digits in a measurement that are known with certainty plus one estimated digit.
Q5. When making measurements using a calibrated device, how do you determine the proper number of significant figures to report that reflect certainty in the measurement?
Background
Topic: Reporting Measurements
This question tests your understanding of how to properly record measurements, including estimating the last digit.
Key Terms
Calibrated device
Significant figures
Certainty and uncertainty in measurement
Step-by-Step Guidance
Identify the smallest division marked on the measuring device.
Record all certain digits (those you can read directly from the scale).
Estimate one digit beyond the smallest marked division; this is the uncertain digit.
Try solving on your own before revealing the answer!
Final Answer:
Report all certain digits plus one estimated digit (the first uncertain digit) when recording a measurement from a calibrated device.
Q6. When dealing with a measured number, what are the cases when a zero is significant? Not significant?
Background
Topic: Significant Figures and Zeros
This question tests your ability to apply the rules for determining which zeros in a number are significant.
Key Terms
Leading zeros
Captive (embedded) zeros
Trailing zeros
Step-by-Step Guidance
Recall the rules for zeros at the beginning (leading), middle (captive), and end (trailing) of a number.
Consider whether the number has a decimal point, as this affects the significance of trailing zeros.
Apply these rules to determine which zeros are significant in different cases.
Try solving on your own before revealing the answer!
Final Answer:
Leading zeros (before the first nonzero digit) are not significant.
Captive zeros (between nonzero digits) are always significant.
Trailing zeros are significant if there is a decimal point present.
Q7. What are the rules for significant figures in addition/subtraction and multiplication/division?
Background
Topic: Significant Figures in Calculations
This question tests your understanding of how to determine the correct number of significant figures to report in calculated results.
Key Terms
Addition/Subtraction rule
Multiplication/Division rule
Step-by-Step Guidance
For addition and subtraction, focus on the decimal places in each number.
For multiplication and division, focus on the total number of significant figures in each number.
Apply the appropriate rule to determine how many significant figures your answer should have.
Try solving on your own before revealing the answer!
Final Answer:
Addition/Subtraction: The result should have the same number of decimal places as the measurement with the fewest decimal places.
Multiplication/Division: The result should have the same number of significant figures as the measurement with the fewest significant figures.
Q8. What is an exact number?
Background
Topic: Types of Numbers in Chemistry
This question tests your understanding of the difference between measured and exact numbers, which affects significant figures.
Key Terms
Exact number
Measured number
Step-by-Step Guidance
Recall the definition of an exact number and how it is obtained.
Think of examples, such as counting objects or defined relationships.
Consider how exact numbers differ from measured numbers in terms of uncertainty.
Try solving on your own before revealing the answer!
Final Answer:
An exact number is a value known with complete certainty, such as a counted quantity (e.g., 12 eggs) or a defined relationship (e.g., 1 inch = 2.54 cm exactly).
Q9. How do you use an exact number in determining the significant figures to report in an answer/measurement?
Background
Topic: Significant Figures and Exact Numbers
This question tests your understanding of how exact numbers affect the reporting of significant figures in calculations.
Key Terms
Exact number
Significant figures
Step-by-Step Guidance
Recall that exact numbers have no uncertainty and are considered to have infinite significant figures.
Understand that exact numbers do not limit the number of significant figures in a calculation.
Apply this concept when using exact numbers as conversion factors or in calculations.
Try solving on your own before revealing the answer!
Final Answer:
Exact numbers do not affect the number of significant figures in a calculated answer; only measured numbers determine the significant figures to report.
