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Allows us to count by weighing. One mole of a substance has a mass in grams equal to its formula mass.
The molar mass in grams per mole is numereically equal to the formula mass in amu
1amu = 1 gram/mole
6.0221367 * 1023 atoms
6.022 * 1023 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
Mass to Particles
grams -> mole -> atoms
- find molar mass
- Arrange avogadro's number as a conversion factor to cancel out the appropriate units
Conversion within a Chemical Formula-example H2O
- 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 H2O 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
- 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
- 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
smallest whole number ratio of atoms in a 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
- seperate element from compound if necessary
- mass element -> mole element = answer/ smallest unit for all elements being considered.
descibes the chemical reaction
has the same number of each type of atom and the same charge on each side of the equation
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
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