Lecture 4-Chemical Substances and Mole concept
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Molecular and Formula Masses
Calculating Molar Mass
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.
and Formula Masses
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
used for ionic compounds = sum of atomic masses of elements present in the formula.
molar mass for carbon dioxide
down each element
multiply by atomic mass
C = 1 x 12.01 = 12.01 amu
O = 2 x 16.00 = 32.00 amu
: 12.01 + 32.00 = 44.01 amu.
Molecular mass of H2O = (2 ×atomic mass of H) + (1 × atomic mass of O)
= (2×1) + (1 × 16) = 18 amu.
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)
, Ca3(PO4)2 (310)
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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