Chemical Substances


Conversions between grams, moles and atoms



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Lecture 4-Chemical Substances and Mole concept

Conversions between grams, moles and atoms

Interconverting mass, moles and number of particles

  • Determine the number of moles in 85.00 grams of sodium chlorate, NaClO3
  • Determine the number of molecules in 4.6 moles of ethanol, C2H5OH. (1 mole = 6.022 x 1023).

Exercises

  • Determine how many H atoms are in 4.6 moles of ethanol.
  • solve the following questions.
  • Q1: How many atoms of silver are in 3.50 moles of silver?
  • Q2: Determine the number of moles of carbon disulfide in 34.75 grams of CS2.
  • Q3: Determine the number of sulfur atoms in 34.75 grams of CS2.
  • Q4: How many grams of oxygen are present in 5.75 moles of aluminum oxide, Al2O3?
  • Q5: Determine the number of fluorine atoms in 24.24 grams of sulfur hexafluoride SF6.

Determining the Formula of an Unknown compound Empirical and Molecular Formulas

  • Empirical- simplest whole-number ratio of atoms (moles of each element) in a formula (in a compound).
  • Molecular - the “true” ratio of atoms in a formula; often a whole-number multiple of the empirical formula
  • We can determine empirical formulas from % composition data; a good analysis tool.

Empirical Formulas

  • Steps for success
    • Convert given amounts to moles
    • Mole ratio (divide all moles by the smallest number of moles)
    • The numbers represent subscripts.
      • If the numbers are not whole numbers, multiply by some factor to make them whole.
      • Note: on multiplying by an integer the relative number of moles will not change because we multiply all the subscripts by same integer.

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