Compounds and Stoichiometry

Question 1

compounds

Answer 1

substances composed of two or more elements in a fixed composition

Question 2

molecular weight

Answer 2

mass (in amu) of the constituent atoms in a compound as indicated by the molecular formula

Question 3

molar mass

Answer 3

mass of one mole of a compound; measured in grams per mol

Question 4

Avogadro’s number

Answer 4

6.022 x 10^23

Question 5

gram equivalent weight

Answer 5

a measure of the mass of a substance that can donate one equivalent of the species of interest
GEW = molar mass/n

Question 6

normality

Answer 6

ratio of equivalents per liter; related to molarity by multiplying the molarity by the number of equivalents present per mole of compound

Question 7

equivalents

Answer 7

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)

Question 8

law of constant composition

Answer 8

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

Question 9

empirical formula

Answer 9

smallest whole-number ratio of the elements in a compound

Question 10

molecular formula

Answer 10

either the same as or a multiple of the empirical formula; gives the exact number of atoms of each element in a compound

Question 11

calculating percent composition by mass

Answer 11

determine mass of individual element and divide by the molar mass of the compound

Question 12

combination reactions

Answer 12

occur when two or more reactants combine to form one product

Question 13

decomposition reactions

Answer 13

occur when one reactant is chemically broken down into two or more products

Question 14

combustion reactions

Answer 14

occur when a fuel and an oxidant (typically O) react, forming the products H2O and CO2 (if the fuel is a hydrocarbon)

Question 15

displacement reactions

Answer 15

occur when one or more atoms or ions of one compound are replaced with one or more atoms or ions of another compound

Question 16

single-displacement reactions

Answer 16

occur when an ion of one compound is replaced with another element

Question 17

double-displacement reactions

Answer 17

occur when elements from two different compounds trade places with each other to form two new compounds

Question 18

neutralization reactions

Answer 18

when an acid reacts with a base to form a salt (and, usually, H2O)

Question 19

determining balanced equations

Answer 19

in order to perform stoichiometric calculations

1. balance least common atoms
2. balance more common atoms (H and O)
3. balance charge, if necessary

Question 20

limiting reagent

Answer 20

determined by balanced equations; reactant that will be consumed first in a chemical reaction

Question 21

excess reagents

Answer 21

other reactants present besides limiting reagent

Question 22

theoretical yield

Answer 22

amount of product generated if all of the limiting reactant is consumed with no side reactions

Question 23

actual yield

Answer 23

typically lower than the theoretical yield

Question 24

percent yield

Answer 24

calculated by dividing actual yield by theoretical yield and converting to percentage
% yield = (actual yield/theoretical yield) x 100

Question 25

Roman numerals (ions)

Answer 25

used for non representative elements to denote charge

Question 26

-ous ending (ions)

Answer 26

indicate lesser charge

Question 27

-ic ending (ions)

Answer 27

indicate greater charge

Question 28

-ide (ions)

Answer 28

all monoatomic anions

Question 29

oxyanions

Answer 29

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

Question 30

hydrogen or bi- (ions)

Answer 30

denotes single H in polyatomic ions

Question 31

dihydrogen (ions)

Answer 31

denotes two H’s in polyatomic ions

Question 32

ion charges

Answer 32

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

Question 33

electrolytes

Answer 33

contain equivalents of ions from molecules that dissociate in solution

Question 34

degree of solvation/dissociation

Answer 34

determines strength of electrolyte

Question 35

Moles from mass

Answer 35

moles = mass of a sample/molar mass

Question 36

equivalents from mass

Answer 36

equivalents = mass of compound/gram equivalent weight

Question 37

molarity from normality

Answer 37

molarity = molar mass/n

Question 38

percent composition

Answer 38

% composition = (mass of element in formula/molar mass) x 100