Chemistry - SCH3U - Unit 4 - Quantitative Chemistry - Note

Intro to the mole

Quantitative chemistry

  • Chemistry involving measurement

  • Quantitative observation

  • Typically refer measurement of mass

Problem

  • To have precision need to know number atom/molecule involved

Solution

  • Relative size scale created for atom

  • Conversion factor created

    • Allowed convert between mass and number atom/molecule in sample

Relative vs absolute scale

  • Relative scale

    • Comparison 1 thing to another

      • Ex

        • How much bigger than Earth is Jupiter

          • Can talk mass but number huge

            • Making it meaningless

  • Absolute scale

    • Exact measurment based on standard

      • Ex

        • Mass determined based on scale that calibrated using standard units

Relative scale in chemistry

  • 2H2H_2 + O2O_2 → 2H2H_2 O

  • Balanced chemical equation

    • Tell every 1 oxygen need 2 hydrogen

Avogadros hypothesis

  • Equal volumes of gases, at same temperature and pressure, contain same number of particle

    • In gases particle not attracted each other

    • Volume gas affected by

      • Temperature (higher T = higher V)

      • Pressure (higher P = lower V)

      • Number particle (higher # = higher V)

    • If V,P,T all same number particles also same

  • Allowed scientist compare sample of gas with same volume and build relative scale of mass compared to hydrogen

    • Hydrogen (H)

      • Relative mass: 1

    • Helium (He)

      • Relative mass: 4

    • Nitrogen (N)

      • Relative mass: 14

    • Oxygen (O)

      • Relative mass: 16

Using relative scale

  • 2H2H_2 + O2O_2 → 2H2H_2 O

  • If 1kg oxygen what mass of hydrogen

    • Need twice as many hydrogen molecule as oxygen molecule

    • Oxygen weigh 16x more then hydrogen

  • Solving

    • 1000g / 16 = 62.6g

    • 62.5 × 2 = 125g

  • Therefore need mass of 125g of hydrogen for 1kg of oxygen

  • If determine mass one type atom can use relative scale determine mass other element

  • Problem

    • Need way go from atomic (microscopic) level to everday (macroscopic) level

  • Solution

    • Develop word that means group of something

The mole

  • 1 mole = 6.0 x 10^23