lecture recording on 22 January 2025 at 16.29.26 PM

Conversion Problems Overview

• Topic of Quiz: Focus on unit conversions for the upcoming quiz on Monday.

Example 1: Converting miles to inches

• Problem: Convert 5.8 miles to inches.

• Conversion Factor: 1 mile = 63,360 inches.

• Set Up the Calculation:

  • Desired units: inches on top to cancel out miles.

  • Calculation:

    • (5.8 miles) * (63,360 inches / 1 mile)

    • Output: Approximately 367488 inches.

• Significant Figures:

  • Original measurement has 2 significant figures.

  • Final answer: 3.7 x 10^5 inches.

Example 2: Converting miles per hour to meters per second

• Problem: Convert 231 miles per hour to meters per second.

• Conversion Factors:

  • 1 mile = 1609 meters

  • 1 hour = 3600 seconds

• Set Up the Calculation:

  • Calculation:

    • (231 miles / 1 hour) * (1609 meters / 1 mile) * (1 hour / 3600 seconds)

• Final Output Calculation:

  • Answer should result in meters per second, approximately calculated from the multiplication and division of the conversion factors.

Example 3: Density Calculation

• Density Formula: Density (D) = Mass (m) / Volume (V)

• Given Values:

  • Mass = 30.01 grams

  • Volume = Final volume after displacement of 62.6 mL - Initial volume of 56.3 mL = 6.3 mL

• Calculation:

  • D = 30.01 grams / 6.3 mL

• Determining Significant Figures:

  • Result rounded to 2 significant figures = 4.8 grams/mL.

Physical vs. Chemical Properties

Definitions

• Physical Properties: Traits that can be observed without changing the substance (e.g., color, texture).

• Chemical Properties: Traits that indicate how a substance reacts to form new substances and change chemically (e.g., combustion).

Examples

• Physical Change Examples: Cutting, boiling water.

• Chemical Change Examples: Iron rusting, milk souring.

Temperature Conversions

• Conversion Formula: K = °C + 273

• Sample Calculation: Convert from Celsius to Kelvin and Fahrenheit:

  • Convert 2.73K to Celsius: °C = K - 273 = -270.27°C.

  • Convert to Fahrenheit: °F = (°C * 9/5) + 32 = -454.449°F.

Atomic Weight and Moles

• Calculating Moles:

  • Use Atomic Weight to determine moles from grams (e.g., NaCl calculation).

• Formula:

  • Moles of a substance = (mass in grams) / (molar mass).

Example: Moles Calculation

• For 25g of NaCl:

  • Calculate atomic weight of Na (23) + Cl (35) = 58g/mol.

  • Moles = 25g / 58g/mol = approximately 0.43.

Polarity of Molecules

Definitions

• Polar Molecules: Unequal sharing of electrons leading to charges (e.g., water).

• Non-Polar Molecules: Equal sharing of electrons (e.g., O2, N2).

Examples

• Identifying Polarity:

  • Water (H2O) = Polar

  • Dihydrogen (H2) = Non-Polar

• Solubility:

  • Polar dissolves polar, non-polar dissolves non-polar.

  • Example: NaCl in water (ionic dissolves in polar).

Conclusion on Review Content

• Focus on mastering conversion problems, understanding physical and chemical changes, properties of matter, temperature conversions, and the significance of significant figures.

• Prepare for practical applications in density and atomic weight calculations.