Moles Test

Unit 6: The Mole Test

Concepts:

• What is a mole? What is it based on?

  • A mole is 6.02 x 1023

  • It is based on how many particles are in one mole

• Converting between different units

  • moles to grams

    • y moles x molar mass/ 1 mole   

  • moles to particles 

    • X moles x 6.02 * 1023/1 mole

    • When to use particles, molecules, atoms

      • Atoms : individual elements 

      • Molecules: covalent compounds

      • Particles: ionic compounds

• Calculating molar masses

  • Element

    • Atomic mass (red number on periodic table)

  • Compound

    • Find each elements atomic mass 

    • Multiply it by how many of each element there is in the compound

    • Add all the elements total mass together 

• Percent composition 

  • Equation: % comp = element mass / compound mass x 100 

• Determining empirical formulas from % composition data, OR mass data

  • Make % into g (assuming 100g sample) 

  • Convert grams to moles 

  • Divide each mole value by the smallest mole value. = mole ratio 

    • There is a mole ratio for each element and that will be the subscript for each.  

  • Write the empirical formula using the mole ratio 

• Determining molecular formulas

  • Find the empirical formula 

  • Then find the molecular mass of the empirical formula = molecular mass 

  • Then find the original formulas molecular mass = formula mass 

  • Molecular mass/formula mass = multiply number 

  • Multiply each subscript of the empirical formula by the multiply number 

• Molarity (M) 

  • What does it measure : the number of moles of solute dissolved in liters of solution 

  • Equation:

    • Molarity = moles of solute/liters of solution

• Dilutions

  • Equation: M1V1=M2V2 

    • M1& V1 = initial molarity and volume (volume can be ml and L) 

    • M2& V2 = final molarity and volume (volume can be ml and L) 

  • What units are required for M and V?

    • Molar and ml or L