Allows us to count by weighing. One mole of a substance has a mass in grams equal to its formula mass.
Molar mass
The molar mass in grams per mole is numereically equal to the formula mass in amu
1amu = 1 gram/mole
Avogdro's number
6.0221367 * 10^{23} atoms
6.022 * 10^{23 }atoms / mole
Calculating molar mass
1. look at the # of atoms of one type in the formula
2. look on the periodic chart for the mass of that atom.
3. multiply the mass by the number of atoms
4. do this for each type of atom, then add them up
molar mass has units of grams/mole
Mass to Moles
Calculatge the molar mass
Arrange the molar mass as a conversion factor to cancel out the appropritate units
Calculate
Mass to Particles
grams -> mole -> atoms
find molar mass
Arrange avogadro's number as a conversion factor to cancel out the appropriate units
Calculate
Conversion within a Chemical Formula-example H_{}_{2}O
Stoichiometic equivalency (pertaining to or involving substances that are in the exact proportions required for a given reaction) between any two atoms or compounds.
2atoms H / 1 H_{2}O molecule
2 mole H atom / 1 mole O atom
2 atoms H / 1 atom O
Conversion within a Chemical Formula
Mass A <-> Moles A <-> Moles B <-> Mass B
find molar mass
set up dimensional analysis and calculate
Percentage Composition
list of elements in a compound by percentages of mass (parts per hundred)
can be calculated from decomposition data or from chemical formula. part / whole * 100
percentages should equal 100%
Theoretical percentages by mass
Assume 1 mole sample
calculate molar mass - convert from mole to gram then add mass together
calculate percentage composition. parts / whole * 100
Combustion analysis
Involves burining a sample of a compound to determine its chemical formula
Compounds are seldom broken up into their elements-they are changed into other compounds
Elementa Combustion Analysis
Calculate part of each element in the compound.
mass compound ->mole compound -> mole element ->mass element
Calculate the mass percentage
parts / whole * 100
Emperical formula
smallest whole number ratio of atoms in a formula
Molecular formula
actual formula for a molecule
Molecular formula-given empirical formula and molar mass
mass of molecular formula / mass of emirical formula
multiply by empirical formula for molecular formula
Emperical formual-calculation
seperate element from compound if necessary
mass element -> mole element = answer/ smallest unit for all elements being considered.
Chemical equations
descibes the chemical reaction
Balanced equations
has the same number of each type of atom and the same charge on each side of the equation
Coefficients
in a balanced equation it tell us the stoichiometric relationship between the components in a reaction and can be used as conversion factors.
Conversion factors for chemical reactions
Moles A <-> Moles B
write chemical equation and balance it
find stoichiometric relationship between elements
look at units to decide what should be on top, then calculate