Chapter 4 - Kaplan MCAT Gen Chem Review

2025-2026

compounds

substances composed of 2 or more elements in a fixed position

compounds use the terms ____ and ____

formula unit and formula weight

molecule

a combination of 2 or more atoms held together by covalent bonds

atomic weight

weighted average of the masses of the naturally occurring isotopes of an element

molecular weight

the sum of the atomic weights of all the atoms in a molecule (amu/molecule)

formula weight

the sum of the atomic weights of the constituent ions according to its empirical formula (amu/molecule)

molar mass

mass of one mole of a compound (g/mol)

formula for moles

Moles = (mass of sample (g)) / (molar mass (g/mol))

equivalent

how many moles of the thing will one mole of a given compound produce

equivalents are mostly seen in ____ and ____

acid-base chemistry and oxidation-reduction reactions

acid-base chemistry

hydrogen ions or hydroxide ions

oxidation-reduction reactions

moles of electrons or other ions

gram equivalent weight

a measure of the mass of a substance that can donate one equivalent of the species of interest

gram equivalent weight formula

gram equivalent weight = (molar mass) / (n)

n in gram equivalent weight formula

the number of particles of interest produced or consumed per molecule

equivalents formula

equivalents = (mass of compound (g)) / (gram equivalent weight (g))

normality (N)

-the ratio of equivalents per liter

-a measure of concentration

normality assumes that

reaction will proceed to completion

normality formula

Normality = (Molarity)(n)

Molarity = (Normality) / (n)

n in Normality = (Molarity)(n)

number of protons, hydroxide ions, electrons, or ions produced or consumed by the solute

law of constant composition

any pure sample of a given compound will contain the same elements in an identical mass ratio

empirical formula

simplest whole-number ratio of the elements in a compound

____ only have empirical formulas

ionic compounds

molecular formula

-gives exact # of atoms of each element in the compound

-is a multiple of the empirical formula

percent composition

percent of a specific compound that is made up of a given element

percent composition formula

percent composition = [(mass of element in formula) / (molar mass)] (100)

combination reaction

2 or more reactants forming one product

decomposition reaction

single reactant breaks down into 2 or more products

delta (triangle) over reaction arrow represents ___

addition of heat

combustion reaction

involves fuel (usually a hydrocarbon) and an oxidant (normally oxygen)

in a combustion reaction in its most common form, products are usually ____ and ___

carbon dioxide and water

single-displacement reaction

an atom or ion in a compound is replaced by an atom or ion of another element

single displacement reactions are often further classified as

oxidation-reduction reactions

double-displacement reactions

elements from 2 different compounds swap places with each other to form 2 new compounds

double displacement reactions are also called

metathesis reactions

double displacement reactions occur when

-one of the products is removed from the solution as a precipitate or gas

-when 2 of the original species combine to form a weak electrolyte that remains undissociated in solution

neutralization reactions

type of double-displacement reactions in which an acid reacts with a base to produce a salt (and usually water)

law of conservation of mass

the mass of the reactants consumed must equal the mass of products generated

stoichiometric coefficient

number placed in front of each compound to indicate the relative number of moles of a given species in the reaction

balancing reactions steps

1.balance least common atom(s)

2.balance the more common atom(s)

3.balance charge, if necessary

1 mole of any ideal gas at STP (constant)

22.4 L

limiting reagent

the reactant that will be consumed first in a chemical reaction

excess reagents

the reactants that remain after all the limiting reagent is used up

comparisons of reactants must be done in

moles

theoretical yield

maximum amount of product that can be generated as predicted from the balanced equation

theoretical yield assumes that

all limiting reactant is consumed, no side reactions occur, and all product is collected

actual yield

the amount of product one actually obtains during the reaction

percent yield formula

percent yield = [(actual yield) / (theoretical yield)] (100)

hydrogen can be ___ or ___

anion or cation

ionic compounds are held together by

ionic bonds

for elements that can form more than one positive ion, the charge is indicated by

a roman numeral in parentheses following the name of the element

iron(II) = Fe^2+

suffix -ous

lesser charge

suffix -ic

greater charge

monatomic anions are named by

dropping ending of name and adding suffix -ide

hydride = H^-

many polyatomic anions contain

oxygen

polyatomic anions are often called

oxyanions (because many contain oxygen)

suffix -ite

less oxygen

suffix -ate

more oxygen

prefix hypo-

even less oxygen

prefix per-

even more oxygen (hyper)

polyatomic anions often gain 1 or more ____ to form anions of lower charge

H^+ ions

prefix bi-

1 hydrogen

prefix di-

2 of root

oxidation states

some elements can have several different charges

alkali metals have a charge of

+1

alkaline earth metals have a charge of

+2

halogens form monoatomic anions with a charge of

-1

charges of nonrepresentative elements are

not predictible

electrolytes

solutes that enable solutions to carry currents

electrolytes contain equivalents of ions from molecules that

dissociate in solution

strength of an electrolyte depends on its

degree of dissociation, or solvation