4: Compounds and Stoichiometry

Question 1

compounds

Answer 1

pure substances composed of 2+ elements in a fixed proportion

Question 2

molecules

Answer 2

combination of 2+ atoms held together by covalent bonds ex. CO2

Question 3

formula unit

Answer 3

empirical formula of an ionic compound (instead of molecule)

Question 4

Normality (N)

Answer 4

measure of concentration (equivalents/L)

Question 5

Molarity

Answer 5

Normality/n

Question 6

gram equivalent weight in acid base chemistry

Answer 6

mass of acid that yields one mole of protons or mass of base that yields one mole of hydroxide ions

Question 7

law of constant composition

Answer 7

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

Question 8

empirical formula

Answer 8

simplest whole-number ratio of the elements in a compound

Question 9

molecular formula

Answer 9

exact number of atoms of each element in the compound… multiple of empirical

Question 10

percent composition

Answer 10

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

Question 11

combination reaction

Answer 11

2+ reactants forming a product: A + B –> C

Question 12

decomposition reaction

Answer 12

single reactant breaks down into 2+ products: A –> B + C

Question 13

combustion reactions

Answer 13

usually conducted with hydrocarbon fuels and involves oxidation

hydrocarbon + oxygen –> CO2 +H2O

Question 14

single-displacement reaction

Answer 14

atom/ion in a compound is replaced by an atom/ion of another element… aka oxidation-reduction rxns

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

Question 15

double-displacement reactions/metathesis reactions

Answer 15

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

• occurs when one of the products is removed from the solution as a precipitate or gas or when 2 of the original species combine to form a weak electrolye that remains undissociated in solution

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

Question 16

neutralization reactions

Answer 16

specific type of double-displacement reaction in which an acid reacts with a base to produce a salt and water

ex. HCl (aq) + NaOH (aq) –> NaCl (aq) + H2O (l)

Question 17

mole of gas at STP conversion

Answer 17

22.4 L

Question 18

monoatomic anion naming

Answer 18

drop ending of name and add -ide

ex. H^- hydride, F^- Flouride, S^2- Sulfide

Question 19

polyatomic anions/oxyanions

Answer 19

hypo-, -ite, -ate, per-

ex. ClO^- hypochlorite, ClO₂^- chlorite

ClO₃^- chlorate,ClO₄^- perchlorate

ex. NO₂^- Nitrite, NO₃^- Nitrate
ex. SO₃^2- sulfite, SO₄^2- sulfate

Question 20

polyatomic anions with H+ ions

Answer 20

add hydrogen or dihydrogen

ex. HCO₃^- hydrogen carbonate/bicarbonate

HSO₄^- hydrogen sulfate/bisulfate

H₂PO₄^- dihydrogen phosphate

Question 21

common polyatomic ions

Answer 21

NH₄⁺ Ammonium

C₂H₃O₂^- Acetate

CN^- Cyanide

MnO₄^- Permanganate

SCN^- thiocyanate

CrO₄^2- chromate

Cr₂O₇^2- dichromate

BO₃^3- borate

Question 22

metals that form more than one positive ion

Answer 22

• charge indicated by Roman numeral in parenthesis
• -ous for lesser charge
• -ic for greater charge

ex. Cu⁺ Copper(I) or Cuprous, Cu²⁺ Copper (II) or Cupric
ex. Fe²⁺ Iron(II) or Ferrous, Fe³⁺ Iron(III) or Ferric

Question 23

electrolytes

Answer 23

solutes that enable solutions to carry currents

• ionic compounds make good electrolytes because they dissolve most readily
• electrical conductivity of aqueous solutions is governed by the presence and concentration of ions in the solution

Question 24

tendency of ionic solvent to solvate

Answer 24

• strong electrolyte if it dissociates completely into its constiuent ions
  
  • ex. NaCl, KI, HCl in water
• weak electrolyte if ionizes or hydrolyzes incompletely in aqueous solution and only some of solute is dissolved into its ionic constituents
  
  • ex. acetic acids, weak acids, ammonia, weak bases
• nonelectrolyte of compound does not ionize at all in water
  
  • ex. nonpolar gases, organic compounds