Unit 3
Home > Flashcards > Print Preview
The flashcards below were created by user
atcannon
on
FreezingBlue Flashcards. What would you like to do?

Mole
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 Formulaexample 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 elementsthey 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 formulagiven empirical formula and molar mass
mass of molecular formula / mass of emirical formula
multiply by empirical formula for molecular formula

Emperical formualcalculation
 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