ch 4 - Compounds and Stoichiometry Flashcards
formula unit
the empirical formula of a compound, used instead of attempting to define certain molecules such as those in coordinated lattices; term used to talk about unit because no molecule of it exists because ionic compounds automatically create a lattice
formula weight
weight of units that do not exist as just molecules (therefore molecular weight becomes meaningless). Found by adding up the atomic weights of the constituent ions according to its empirical formula, units are amu per molecule
atomic weight
weighted average of the masses of the naturally occurring isotopes of an element, not their weights
molecular weight
sum of the atomic weights of all the atoms in a molecule; measured in atomic mass units (amu) per molecule
mole
quantity of any substance equal to the number of particles found in 12 grams of carbon-12
Avogadro’s number (N sub A)
6.022 x 10^23 mol^-1. number of particles in 12 grams of carbon-12
molar mass
mass of one mole of a compound usually expressed in g/mol; don’t interchange with molecular weight which is measured in amu/molecule.
equation for number of moles of a sample substance
moles = mass of sample (g)/molar mass (g/mol)
equivalent
how many moles of the thing we are interested in (protons, hydroxide ions, electrons, or ions) will one mole of a given compound produce?
gram equivalent weight
the amount of a compound, measured in grams, that produces one equivalent of the particle of interest; calculated from: gram equivalent weight = molar mass/n; where n = the number of particles of interest produced or consumed per molecule of the compound in the reaction. ex: one needs only 31 grams of H2CO3 (molar mass = 62 g/mol) to produce one equivalent of hydrogen ions because each molecule of H2CO3 can donate two hydrogen ions (n = 2)
equation to find out how many equivalents are present if the amount of compound in a reaction is known
equivalents = mass of compound (g)/gram equivalent weight (g)
normality (N)
measurement of concentration, given in units equivalents/L; mostly used on the mcat to refer to hydrogen: a 1 N solution of acid contains a concentration of hydrogen ions equal to 1 mole per liter; 2 N contains a concentration = to 2 moles per liter
conversion from normality to molarity of a given solution
Molarity = normality/n; where n is the number of protons, hydroxide ions, electrons, or ions produced or consumed by the solute
molarity
moles of solute/L of solution
law of constant composition
states that any pure sample of a given compound will contain the same elements in an identical mass ratio
empirical formula
gives the simplest whole-number ratio of the elements in a compound
molecular formula
gives the exact number of atoms of each element in the compound and is a multiple of the empirical formula
empirical formula for monosaccharides
CH2O
percent composition
the percent of a specific compound that is made up of a given element; equation is percent composition = (mass of element in formula/molar mass) x 100%
Combination reaction
has two or more reactants forming one product
decomposition reaction
opposite of combination reaction: a single reactant breaks down into two or more products, usually as a result of heating, high-frequency radiation, or electrolysis
combustion reaction
a special type of reaction that involves fuel - usually a hydrocarbon - and an oxidant (normally oxygen)
single-displacement reaction
occurs when an atom or ion in a compound is replaced by an atom or ion of another element (ex: Cu + AgNO3 -> Ag + CuNO3
double-displacement reactions
also called metathesis reactions: elements from two different compounds swap places with each other to form two new compounds
Neutralization reactions
specific type of double-displacement reaction in which an acid reacts with a base to produce salt (and, usually, water)
Stoichiometric coefficients
numbers placed in front of each compound
limiting reagent
limits the amount of product that can be formed in the reaction
excess reagents
reactants that remain after all the limiting reagent is used up
principles for determining rate limiting reactant
- All comparisons of reactants must be done in units of moles not grams. 2. It is not absolute mole quantities of reactants that determine which reactant is limiting. Rather, rate at which the reactants are consumed (stoichiometric ratios of reactants), combined with absolute mole qualities determines which one is limiting
yield of a reaction
can refer to either the amount of product predicted (theoretical yield) or actually obtained (raw or actual yield)
calculating theoretical yield
Remember to balance the equation! amount in grams of limiting reagent put in multiplied (molar mass of product over molar mass of limiting reagent x number of moles of limiting reagent needed to produce 1 mole of product) - note: they use fractions with units in order to cancel out units, but this should be obvious (actual is grams of limiting reagent x (1 mol limiting reagent/ grams molar mass of limiting reagent)x(1 mol product/1 mol limiting reagent)x(molar mass product/1 mol product) = theoretical yield of product; no need to calculate number of moles of reactant by the grams given typically
rules for nomenclature with oxyanions
when an element forms two oxyanions, the name of the one with less oxygen ends in -ite and the one with more ends in -ate: (NO2)- : Nitrite; (NO3)- : Nitrate; (SO3)2- : Sulfite; (SO4)2- : Sulfate
rules for nomenclature of extended series of oxyanions
hypo- used as prefix or hyper written as per-, indicate less oxygen and more oxygen: ClO- : Hypochlorite; (ClO2)- : Chlorite; (ClO3)- : Chlorate; (ClO4)- : Perchlorate
naming polyatomic anions that gain one or more H+ ions to form anions of lower charge
named by adding the word hydrogen or dihydrogen; or using prefix bi-; (HCO3)- : Hydrogen carbonate or bicarbonate; (HSO4)- : Hydrogen sulfate or bisulfate; (H2PO4)- : Dihydrogen phosphate
useful to know polyatomic ions
Ammonium (NH4)+; Acetate (C2H3O2)-; cyanide CN-; Permanganate (MnO4)-; Thiocyanate SCN-; Chromate (CrO4)2-; Dichromate (Cr2O7)2-; Borate (BO3)3-
electrolytes
solutes that enable solutions to carry currents
solvate
verb meaning to dissolve
acetone
propanone
other option for calculating theoretical yield
number of moles of reactant given (such as 30 g of H2O is 1.7 moles) divided by the number of moles required to create one mole of product x the molecular weight of product given
