# 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
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• 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)

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