Overview
This lecture covers measurement in chemistry, the metric system and its prefixes, how to set up and use conversion factors, and key unit equalities needed for lab work and homework.
Measurement Basics
- Every measurement consists of a number, a unit, and the substance measured for clear scientific communication.
- Always include all three parts in your answer unless the substance is obvious or unchanging throughout the problem.
Metric System & Base Units
- Chemistry uses the metric system, not the English system.
- Base units: meter (m) for length, gram (g) for mass, liter (L) for volume, and second (s) for time.
- Use uppercase "L" for liters to avoid confusion.
Metric Prefixes & Memorization
- Metric prefixes indicate powers of ten (e.g., kilo = 10³, centi = 10⁻², milli = 10⁻³).
- Memorize prefix names, symbols, and scientific notation for each (refer to Table 1.2).
- Prefixes can represent large (kilo, mega, giga) or small values (centi, milli, micro, nano).
- Create flashcards: one side with prefix and symbol, the other with scientific notation.
Setting Up Equalities
- Prefix-base unit pairs form equalities (e.g., 1 km = 1,000 m; 1 mg = 10⁻³ g).
- When converting, switch the exponent sign if you change which side the exponent is on.
Types of Volume & Conversions
- Volume can be liter-based (L, mL) or length-cubed-based (cm³, m³).
- 1 mL = 1 cm³ = 1 cc (cubic centimeter), commonly used in healthcare.
English-Metric Conversions
- Key conversions to memorize:
- 1 foot = 12 inches
- 1 inch = 2.54 cm (exact)
- 1 kg = 2.205 lb
Conversion Factors & Dimensional Analysis
- To convert units, multiply by a fraction (conversion factor) where units cancel out.
- Conversion factors must represent equal quantities (e.g., 1 kg / 2.205 lb or vice versa).
- Multiplying by a conversion factor changes the unit but not the actual quantity.
Example: Milligrams to Grams
- Use the equality: 1 g = 1,000 mg or 1 mg = 10⁻³ g.
- Set up the fraction so the units you want to cancel are opposite each other (e.g., mg cancels with mg).
Key Terms & Definitions
- Measurement — A value made up of a number, unit, and substance.
- Metric Prefix — A symbol/word used before a base unit to indicate power-of-ten multiples.
- Conversion Factor — A fraction representing the equality of two different units.
- Base Unit — The fundamental unit for a type of measurement (meter, gram, liter, second).
Action Items / Next Steps
- Memorize metric prefixes, base units, and key English-metric conversion equalities.
- Create flashcards for prefixes (name, symbol, scientific notation).
- Practice setting up and using conversion factors for homework assignments.