Ch4: Compounds and Stoichiometry

Molecule

2+ atoms connected by covalent bonds

Compounds

Pure substance composed of 2+ elements in fixed proportion

Formula Unit/Weight

Describe molecule and weight of ionic compounds

Molecular Weight

Sum of atomic weights of atoms in molecule

amu/molecule

Molar Mass

Mass of 1 mole of compound

g/mol

Equivalents

Moles of thing of interested produced by 1 mole of compound

Gram Equivalent Weight

g of compound producing 1 equivalent of particle of interest

Normality (N)

Measure conc (assume reaction proceed to completion)

Common for H+ conc

Equivalents/L

Normality and Molarity

1N HCl = 1M HCl (monoprotic)

1N H2CO3 = 0.5M H2CO3 (diprotic)

Structural Formula

Show bonds between atoms in compound

Law of Constant Composition

Pure sample contains same elements in same mass ratio

Empirical Formula

Smallest whole-number ratio of elements in compound

Ex: Benzene = CH

Molecular Formula

Exact number of atoms in compound

Multiple of empirical formula

Ex: Benzene = C6H6

Percent Composition

Percent of compound made up of specific element

Combination Reactions

2+ reactants form 1 product

A + B → C

Decomposition Reactions

1 reactant breakdown into 2+ products

Usually from heating, high frequency radiation, electrolysis

A → B + C

Combustion Reactions

Fuel (hydrocarbon) and oxidant (O2) form CO2 and H2O

Single-Displacement Reactions

Atom/ion in compound replaced by another atom/ion

Include redox reactions

Double-Displacement (Metathesis) Reactions

Elements from 2 different compounds switch

1 product removed from solution as precipitate/gas OR weak electrolyte undissociated in solution

Neutralization Reactions

Double-displacement

Acid + base → Salt + H2O

Law of Conservation of Mass and Charge

Mass and charge of reactants = mass and charge of products

Stoichiometry Steps (3)

1. Convert from given units to moles
2. Mole ratio
3. Convert moles to desired unit

1 mole of ideal gas at STP

22\.4L

1 mole of substance

6\.022E23 particles

M in grams

Limiting Reagent

Reactant consumed first in reaction

Mole comparisons to identify

Excess Reagents

Reactants remaining after limiting reagent used up

Theoretical Yield

Max product from reaction

Predicted with calculations

Actual Yield

Product obtained from reaction

Multicharge Ions

Roman numerals

\-ous: Lesser charge

\-ic: Greater charge

Oxyanions

Polyatomic anions containing oxygen

Hypo-ite: Least O

\-ite: Less O

\-ate: More O

Per-ate: Most O

Polyatomic Anions With H+

Hydrogen/Bi-: Gain 1 H+

Dihydrogen: Gain 2 H+

Anions with Metals

Metals: Positive oxidation state

Ex: Permanganate (MnO4-), chromate (CrO4 2-)

Oxyanions with Halogens

Halogen has positive oxidation state

Solid Ionic Compunds

Poor conductors

Charged particles stuck in lattice structure

Aqueous Ionic Compunds

Good conductors

Ion-dipole interactions between ions and water molecules disrupt lattice arrangement

Electrolytes

Solutes enabling solution to carry current

Conductivity increases with increasing free ions/e in solution

Strong Electrolyte

Solute dissociate completely in solution

Ex: NaCl, KI, highly polar molecules (HCl)

Weak Electrolyte

Solute dissociate incompletely in solution

Ex: Hg2I2, acetic acid, weak acids and bases

Nonelectrolytes

Do not ionize in water

Ex: Nonpolar gases, organic compounds, glucose