Stoichiometry Flashcards
Compound
A pure substance composed of two or more elements in a fixed proportion.
Molecule
A combination of two or more atoms held together by covalent bonds, and is the smallest unit of a compound that still displays the properties of that compound.
Formula Mass
Used in the place of molecular mass in the case or describing ionic compounds as they do not form true molecules
Molecular Mass
Also known as “molecular weight”, is the sum of the atomic masses of the atoms in the molecule.
Avagadro’s number
6.022x10^23
of moles in sample =
Weight of sample (g)/ Molecular weight (g/mol)
Gram-equivalent weight (GEW)
molar mass/n
Law of constant composition
All samples of a given compound will contain the same elements in identical mass ratios
Emperical formula
Gives the simplest whole number ratio of the elements in the compound
Molecular formula
Gives the exact number of atoms of each element, and is a multiple of the emperical formula
True or false: An ion will only have and emperical formula and not a molecular formula
True
Percent composition
The mass percent of the element is a specific compound
%=mass of element/formula weight
True or False: The percent composition can be found using the emperical or molecular formula
True
To find the molecular formula from percent compositions and molecular weight
of moles of element = (% composition)(molecular mass) / (molar mass of element)
To find the emperical formula from percent compositions
- Divide the percent (not decimal) by molar mass of each element
- Divide each ratio by smallest ratio
- Multiply the ratios to get whole numbers
