Ch. 4: Compounds and Stoichiometry

Question 1

what are the two laws of conservation that must be followed when balancing chemical equations?

Answer 1

1. law of conservation of mass
2. law of conservation of charge

the number of atoms of each element on the reactant side equals the number of atoms of that element on the product side

Question 2

what do stoichiometric coefficients indicate?

Answer 2

these are the numbers placed in front of each compound

used to indicate the relative number of moles of a given species involved in the reaction

Question 3

what are the steps to balancing a chemical reaction?

Answer 3

see p. 138

Question 4

defn: molecule

Answer 4

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

ionic compounds do not form true molecules because of the way in which the oppositely charged ions arrange themselves in the solid state = technically a formula unit with a formula weight

Question 5

defn + unit: molecular weight

Answer 5

the sum of the atomic weights of all the atoms in a molecule
units are atomic mass units (amu) per molecule

Question 6

defn + unit: formula weight

Answer 6

of an ionic compound

the sum of the atomic weights of the constituent ions according to its empirical formula

units: amu per molecule

Question 7

defn: mole

Answer 7

a quantity of any substance equal to the number of particles that are found in 12 grams of carbon-12 (Avogadro’s number)

one mole of a compound has a mass in grams equal to the molecular or formula weight of the compound in amu

Question 8

defn: Avogadro’s number

Answer 8

6.022 x 10^23 mol^-1

Question 9

defn + unit: molar mass

Answer 9

the mass of one mole of a compound

unit: g/mol

Question 10

defn: equivalents

Answer 10

how many moles of the thing we are interested in (protons, hydroxide ions, electrons, or ions) will one mole of a given compound produce?

Question 11

defn + eqn: gram equivalent weight

Answer 11

the amount of a compound (in grams) that produces one equivalent of the particle of interest

gram equivalent weight = molar mass/n

where n is the number of particles of interest produced or consumed per molecule of the compound in the reaction

Question 12

eqn: if the amount of a compound is known and we need to determine how many equivalents are present:

Answer 12

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

Question 13

defn: normality (N)

Answer 13

a measure of concentration given in the units equivalents/L

always assume that a reaction will proceed to completion

Question 14

eqn: conversion from normality to molarity of a given solute

Answer 14

Molarity = Normality/n

where n is the number of protons, hydroxide ions, electrons, or ions produced or consume by the solute

Question 15

defn: structural formulas

Answer 15

skeletal representations of compounds that show the various bonds between the constituent atoms of a compound

Question 16

defn: law of constant composition

Answer 16

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

Question 17

defn: empirical formula vs. molecular formula

Answer 17

EMPIRICAL = gives the simplest whole-number ratio of the elements in the compound

MOLECULAR = gives the exact number of atoms of each element in the compound (is a multiple of the empirical formula)

Question 18

defn + eqn: percent composition

Answer 18

percent composition of an element (by mass) = the percent of a specific compound that is made up of a given element

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

can use empirical or molecular formula

Question 19

defn: combination reaction

Answer 19

has two or more reactants forming one product

A + B –> C

Question 20

defn: decomposition reaction

Answer 20

the opposite of a combination reaction

a single reactant breaks down into two or more products, usually as a result of heating, high-frequency radiation, or electrolysis

A –> B + C

Question 21

what does the delta sign over a reaction arrow represent?

Answer 21

the addition of heat

Question 22

defn: combustion reaction

Answer 22

a special type of reaction that involves fuel (usually a hydrocarbon) and an oxidant (normally oxygen)

in the most common form: these reactants form the two products of carbon dioxide and water

Question 23

defn: single-displacement reaction

Answer 23

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

ex: Cu (s) + AgNO3 (aq) –> Ag (s) + CuNO3 (aq)

Question 24

defn: double-displacement reactions (metathesis reactions)

Answer 24

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

occurs when one of the products is removed from the solution as a precipitate or gas when two of the original combine to form a weak electrolyte that remains undissociated in solution

ex: CaCl2 (aq) + 2 AgNO3 (aq) –> Ca(NO3)2 (aq) + 2 AgCl (s)

Question 25

defn: neutralization reactions

Answer 25

a specific type of double-displacement reaction in which an acid reacts with a base to produce a salt (and usually water) ex: HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O (l)

Question 26

when balancing equations, should you focus on the least represented elements first or the most represented elements first?

Answer 26

LEAST then work your way to the most

Question 27

defn: limiting reagent/reactant

Answer 27

the reactant that is used up or consumed first in a reaction it limits the amount of product that can be formed in the reaction

Question 28

defn: excess reagents (reactants)

Answer 28

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

Question 29

what are the 2 principles to keep in mind when determining the limiting reagent?

Answer 29

1. all comparisons of reactants must be done in units of moles (gram-to-gram comparisons will be useless or misleading) 2. it is not the absolute mole quantities of the reactants that determine which reactant is the limiting reagent --> instead the rate at which the reactants are consumed (the stoichiometric ratios of the reactants), combined with the absolute mole quantities determines which reactant is the limiting reagent

Question 30

defn: theoretical yield vs. actual yield

Answer 30

THEORETICAL = the maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected ACTUAL = the amount of product one actually obtains during the reaction

Question 31

defn + eqn: percent yield

Answer 31

the ratio of the actual yield to the theoretical yield, multiplied by 100 percent yield = actual yield/theoretical yield x 100%

Question 32

defn: ferrous vs. ferric cuprous vs. cupric

Answer 32

FERROUS = Fe2+ FERRIC = Fe3+ CUPROUS = Cu+ CUPRIC = Cu2+

Question 33

how are monatomic anions named?

Answer 33

by dropping the ending of the name of the element and adding -ide H- = hydride F- = fluoride O2- = oxide S2-= sulfide N3- = nitride P3- = phosphide

Question 34

how are polyatomic anions that contain oxygen (oxyanions) named?

Answer 34

when an element forms two oxyanions, the name of the one with less oxygen ends in -ite, and the one with more oxygen ends in -ate NO2- = nitrite NO3- = nitrate SO32- = sulfite SO42- = sulfate

Question 35

mnemonic: oxyanions

Answer 35

the lITEst anions have the fewest oxygens the heaviest anions ATE the most oxygens

Question 36

defn: hypo- and per- (ionic compound nomenclature)

Answer 36

hypo- = less oxygen per- = more oxygen ClO- = hypochlorite ClO2- = chlorite ClO3- = chlorate ClO4- = perchlorate

Question 37

how are polyatomic anions that gain one or more H+ ions to form anions of lower charge named?

Answer 37

by adding the word hydrogen or dihydrogen to the front of the anion's name HCO3- = hydrogen carbonate OR bicarbonate HSO4- = hydrogen sulfate OR bisulfate H2PO4- = dihydrogen phosphate

Question 38

why are ionic compounds good conductors of electricity in aqueous solutions?

Answer 38

the lattice arrangement is disrupted by the ion-dipole interactions between the ionic components and the water molecules the cations and anions are now free to move and the solution of ions is able to conduct electricity

Question 39

defn: electrolytes

Answer 39

solutes that enable solutions to carry currents the electrical conductivity of aqueous solutions is governed by the presence and concentration of ions in the solution

Question 40

defn: strong electrolyte vs. weak electrolyte vs. nonelectrolyte

Answer 40

a solute is considered a strong electrolyte if it dissociates completely into its constituent ions weak electrolyte: ionizes or hydrolyzes incompletely in aqueous solution and only some of the solute is dissolved into its ionic constituents nonelectrolyte = compounds that do not ionize at all in water, retaining their molecular structure in solution