Chemical Substances

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

• Calculate the molar mass for carbon dioxide, CO2
• Write down each element; multiply by atomic mass
• C = 1 x 12.01 = 12.01 amu
• O = 2 x 16.00 = 32.00 amu
• Total: 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)
• 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

Download 1.07 Mb.

Share with your friends: