Compounds and Stoichiometry Flashcards
compounds
substances composed of two or more elements in a fixed composition
molecular weight
mass (in amu) of the constituent atoms in a compound as indicated by the molecular formula
molar mass
mass of one mole of a compound; measured in grams per mol
Avogadro’s number
6.022 x 10^23
gram equivalent weight
a measure of the mass of a substance that can donate one equivalent of the species of interest
GEW = molar mass/n
normality
ratio of equivalents per liter; related to molarity by multiplying the molarity by the number of equivalents present per mole of compound
equivalents
moles of the species of interest; most often seen in acid-base chemistry (H+ ions or -OH ions) and redox reactions (moles of e-‘s or other ions)
law of constant composition
any pure sample of a compound will contain the same elements in the same mass ratio
empirical formula
smallest whole-number ratio of the elements in a compound
molecular formula
either the same as or a multiple of the empirical formula; gives the exact number of atoms of each element in a compound
calculating percent composition by mass
determine mass of individual element and divide by the molar mass of the compound
combination reactions
occur when two or more reactants combine to form one product
decomposition reactions
occur when one reactant is chemically broken down into two or more products
combustion reactions
occur when a fuel and an oxidant (typically O) react, forming the products H2O and CO2 (if the fuel is a hydrocarbon)
displacement reactions
occur when one or more atoms or ions of one compound are replaced with one or more atoms or ions of another compound
single-displacement reactions
occur when an ion of one compound is replaced with another element
double-displacement reactions
occur when elements from two different compounds trade places with each other to form two new compounds
neutralization reactions
when an acid reacts with a base to form a salt (and, usually, H2O)
determining balanced equations
in order to perform stoichiometric calculations
- balance least common atoms
- balance more common atoms (H and O)
- balance charge, if necessary
limiting reagent
determined by balanced equations; reactant that will be consumed first in a chemical reaction
excess reagents
other reactants present besides limiting reagent
theoretical yield
amount of product generated if all of the limiting reactant is consumed with no side reactions
actual yield
typically lower than the theoretical yield
percent yield
calculated by dividing actual yield by theoretical yield and converting to percentage
% yield = (actual yield/theoretical yield) x 100
Roman numerals (ions)
used for non representative elements to denote charge
-ous ending (ions)
indicate lesser charge
-ic ending (ions)
indicate greater charge
-ide (ions)
all monoatomic anions
oxyanions
given a suffix to indicate how oxidized central atom is -ite --> contain lesser amount of O -ate --> contain greater amount of O hypo- --> species with fewest O per- --> species with most O
hydrogen or bi- (ions)
denotes single H in polyatomic ions
dihydrogen (ions)
denotes two H’s in polyatomic ions
ion charges
predictable by group # and type of element (metal or nonmetal) for representative elements but generally unpredictable for non representative elements
- metals form positively charged cations based on group #
- nonmetals form negatively charged anions based on # of e-‘s needed to achieve octet
electrolytes
contain equivalents of ions from molecules that dissociate in solution
degree of solvation/dissociation
determines strength of electrolyte
Moles from mass
moles = mass of a sample/molar mass
equivalents from mass
equivalents = mass of compound/gram equivalent weight
molarity from normality
molarity = molar mass/n
percent composition
% composition = (mass of element in formula/molar mass) x 100
