CHE130 L2

Important Reminders

  • Review Practice Problems from today

  • Familiarize yourself with D2L

  • Read sections 2.1-2.2

  • Register for Aktiv Chemistry

  • HW 1 due Thursday, September 18

The Domains of Chemistry

  • There are three domains of chemistry: Macroscopic, Microscopic, and Symbolic.

  • Classification of examples based on domains:

    • A molecule contains two H atoms and one O atom - Symbolic (due to the use of symbols), but also Microscopic

    • An adult cow weighs 2,400 lbs - Macroscopic

    • I have 15 g of Cu wire - Symbolic and Macroscopic

    • A water molecule is composed of three atoms - Microscopic

Practice Problems

  • Convert 3.5 x 10^{-6} Mg to g

  • Convert 5.23 x 10^{-7} m to an appropriate prefix

  • Convert 1353 mL to L

  • Common SI prefixes and their factors:

    • femto (f): 10^{-15}

    • pico (p): 10^{-12}

    • nano (n): 10^{-9}

    • micro (μ): 10^{-6}

    • milli (m): 10^{-3}

    • centi (c): 10^{-2}

    • deci (d): 10^{-1}

    • kilo (k): 10^{3}

    • mega (M): 10^{6}

    • giga (G): 10^{9}

    • tera (T): 10^{12}

Derived SI Units: Volume

  • Definition: Volume is the measure of the amount of space occupied by an object.

  • Units: Common units include the liter (L) and milliliter (mL).

  • Relations:

    • 1 \text{ dm}^3 = 1 \text{ L}

    • 1 \text{ cm}^3 = 1 \text{ mL}

  • Practice Problem: Convert 5 ft³ to in³
    details provided in class.

Derived SI Units: Density

  • Definition: Density is defined as the ratio of the mass of a substance to its volume.

  • Density of Common Substances:

    • Solids:

    • Ice (at 0 °C): 0.92 \text{ g/cm}^3

    • Oak (wood): 0.60 - 0.90 \text{ g/cm}^3

    • Iron: 7.9 \text{ g/cm}^3

    • Gold: 19.3 \text{ g/cm}^3

    • Liquids:

    • Water: 1.0 \text{ g/cm}^3

    • Ethanol: 0.79 \text{ g/cm}^3

    • Glycerin: 1.26 \text{ g/cm}^3

    • Gases (at 25 °C and 1 atm):

    • Dry air: 1.20 \text{ g/L}

    • Oxygen: 1.31 \text{ g/L}

    • Helium: 0.16 \text{ g/L}

Measurement: Uncertainty, Accuracy, and Precision

  • Measurement Uncertainty:

    • Counting is free from uncertainty and results in exact numbers.

    • Example: The number of apples in a basket is a defined quantity (exact).

    • Derived quantities from measurements have varying degrees of uncertainty due to practical limitations.

    • When recording measurements, you estimate one uncertain digit.

  • Significant Figures:

    • All digits including uncertain last digit are significant figures.

    • For example, density may be represented by a measurement of 21.6 \text{ mL} where:

    • 2 and 1 are certain digits.

    • 6 is the estimated digit, which can vary.

    • Examples of significant figures:

    • Nonzero digits, captive zeros, and trailing zeroes (when to the right of decimal place).

    • Leading zeros and trailing zeros (to the left of the decimal place) are not significant.

Mathematical Treatment of Measurement Results

  • A quantity may need calculation from other measurements.

  • Conversion Factors: Ratios of two equivalent quantities with different measurement units.

  • Common conversion factors include:

    • 1 \text{ in} = 2.54 \text{ cm}

    • 1 \text{ mL} = 1 \text{ cm}^3

    • 1 \text{ ft} = 12 \text{ in}

    • 1 \text{ kg} = 2.2046 \text{ lb}

    • 1 \text{ mile} = 5280 \text{ ft}

  • Practice Example: Convert gas mileage from km/L to miles/gallon.

Conversion of Temperature Units

  • Temperature Definition: The measure of hotness or coldness of a substance.

  • Celsius Scale:

    • Water freezes at 0 °C and boils at 100 °C.

  • Fahrenheit Scale:

    • Water freezes at 32 °F and boils at 212 °F.

    • The intervals have a 100 °C range corresponding to a 180 °F range.

  • Kelvin Scale (SI unit):

    • Absolute temperature scale starting from 0 K

    • Water freezes at 273.15 K and boils at 373.15 K.

  • Conversion formulas:

    • F = 9/5TC + 32

    • K = C + 273.15

  • Practice Problem: Convert 50. °F to °C and K.