Chemical Substances



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Lecture 4-Chemical Substances and Mole concept

Notes

  • A molecular compound is usually composed of two or more elements usually nonmetals. (ionic compounds composed of a metal and a non metal elements)
  • Molecular compounds are named with the first element first and then the second element by using the stem of the element name plus the suffix -ide.
  • Numerical prefixes are used to specify the number of atoms in a molecule.

Molecular and Formula Masses

  • Molecular mass = sum of atomic masses of elements present in the formula unit of the compound.
  • Molecular mass - (also called molecular weight)
  • Formula mass (formula weight)-
    • The mass in amu’s of an ionic compound
    • Formula mass used for ionic compounds = sum of atomic masses of elements present in the formula.

Calculating Molar Mass

  • Formula mass of Ba(NO3)2
  • = (1 × atomic mass of Ba) + (2 × atomic mass of N) + (6 × atomic mass of O)
  • = (1×137.3) + [(2×14) +(6×16)] = 261.3
  • =====================================
  • Exercise: calculate the molecular mass for each of the following compounds:
  • Ibuprofen, C13H18O2 (206).
  • Acetaminophen, C8H9NO2 (151)
  • Aluminum sulfate, Al2(SO4)3 (342)
  • Calcium phosphate, Ca3(PO4)2 (310)

Your Turn!

  • Calculate the molar mass for each of the following:
    • Sulfur trioxide SO3
    • Barium phosphate Ba3(PO4)3
    • Silver nitrate AgNO3
    • Acetic acid CH3COOH

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