U4 - Reactions in Aqueous Solutions

Medium where most chemical reactions and biological processes occur

Water

Solution definition

homogeneous mixture of two or more substances

Solvent definition

substance present in larger amount in solution

Solute definition

substance present in smaller amount in solution

Aqueous solution definition

solution with water as solvent and solute initially a solid or liquid

Electrolyte definition

substance that produces a solution that conducts electricity when dissolved in water

Nonelectrolyte definition

substance that does not conduct electricity when dissolved in water

Factor controlling solution conductivity

number of ions present

Strong electrolyte definition

substance that ionizes completely or undergoes complete dissociation in water

Visual indicator strong electrolyte solution in conductivity test

lightbulb brightly lit

Strong electrolyte examples

ionic compounds and certain acids

Weak electrolyte definition

substance that ionizes incompletely in water

Visual indicator weak electrolyte solution in conductivity test

lightbulb dimly lit

CH3COOH solution process represented by CH3COOH aqueous reversible to CH3COO- and H+

incomplete ionization of weak electrolyte

Symbol indicating incomplete ionization

double arrow

Symbol indicating complete ionization

single arrow

Ionization definition

separation of acids or bases into ions

Chemical equilibrium definition

state where no net change is observed but opposing rates are equal

Water as polar solvent explanation

electrically neutral molecule with positive H atoms and negative O atom poles

Hydration definition

process where ion is surrounded by water molecules

Function of hydration in solution

stabilizes ions and prevents recombining of cations with anions

Composition of HCl aqueous solution

only hydrated H+ and Cl- ions, no hydrated HCl molecules

Substances that conduct electricity in aqueous solutions

electrolytes

Example of weak electrolyte

acetic acid CH3COOH

Precipitation reaction definition

chemical reaction that forms an insoluble product called a precipitate

Precipitate definition

insoluble solid that separates from solution

Metathesis reaction definition

reaction where parts of two compounds exchange cations or anions

Precipitation reactions classification

examples of metathesis reactions

Solubility definition

maximum amount of solute that will dissolve in a given amount of solvent at specific temperature

Soluble substance qualitative definition

fair amount visibly dissolves when added to water

Key fact about ionic compounds in aqueous solution

all ionic compounds are strong electrolytes but not equally soluble

Factor determining precipitate formation

depends on solubility of solute

Highly soluble ionic compounds rule

all compounds containing alkali metal cations, NH4+, NO3-, HCO3-, ClO3- are soluble

Ionic compound behavior in water

break into component cations and anions

Ionic equation definition

equation showing dissolved species as free hydrated ions

Spectator ions definition

ions not involved in overall reaction, appear on both sides of ionic equation

Net ionic equation definition

equation remaining after canceling spectator ions

Step one writing ionic/net ionic equations

write balanced molecular equation and determine insoluble product

Step two writing ionic/net ionic equations

write ionic equation showing non-precipitate compounds as free ions

Step three writing ionic/net ionic equations

identify and cancel spectator ions to get net ionic equation

Net ionic equation final check

charges and number of atoms must balance

Why solid reactants react slowly or not at all

ions locked in place in solid compounds, little mobility prevents contact for reaction

Insoluble compounds solubility nuance

even insoluble compounds dissolve slightly

Product formed Pb(NO3)2 + KI

yellow PbI2 precipitate

Remaining soluble product Pb(NO3)2 + KI

KNO3 remains in solution

BaCl2 + Na2SO4 → BaSO4 + 2NaCl example

molecular equation

Spectator ions BaCl2 + Na2SO4 reaction

Na+ and Cl-

Net ionic equation BaCl2 + Na2SO4 reaction

Ba 2+ + SO4 2- → BaSO4

Key idea predicting precipitate formation

refer to solubility rules

Acids and bases importance

basis of medicinal and household products, important in industrial processes, essential for biological systems

Acid properties

sour taste, change litmus blue to red, react with metals Zn Mg to form H2 gas, aqueous solutions conduct electricity

Base properties

bitter taste, slippery feel like soaps, change litmus red to blue, aqueous solutions conduct electricity

Arrhenius acid definition

substance ionizes in water to give H+ ions

Arrhenius base definition

substance ionizes in water to give OH- ions

Arrhenius limitation

only applies to aqueous solutions

Brønsted acid definition

proton donor

Brønsted base definition

proton acceptor

Brønsted advantage

does not require aqueous solution

Hydronium ion H3O+

hydrated proton H+ aq formed when acid like HCl donates proton to H2O

Strong acid rule

acid ionizes completely in water, single arrow →

Weak acid rule

acid ionizes partially in water, double arrow ⇌

Strong acid example

H2SO4 first ionization step

Weak acid example

HSO4- bisulfate ion

Monoprotic acid definition

yields one H+ per molecule in water

Diprotic acid definition

yields two H+ per molecule in water in two steps

Triprotic acid definition

yields three H+ per molecule in water

Phosphoric acid H3PO4 classification

triprotic acid

Sulfuric acid H2SO4 classification

diprotic acid

Most Brønsted bases characteristic

anions

Molecular base example

NH3 ammonia

Why NH3 is base

reacts partially with H2O to yield NH4+ and OH-

Neutralization reaction definition

reaction between acid and base

Acid-base reaction products

water H2O and salt

Salt definition

ionic compound with cation from base and anion from acid

Net ionic strong acid/base equation

H+ aq + OH- aq → H2O l

Neutralization exception HNO3 + NH3

HNO3 aq + NH3 aq → NH4NO3 aq, no water

Weak acid net ionic rule

weak acid written in molecular undissociated form

Salts that yield gas

carbonates, sulfites, sulfides react with acids to form CO2, SO2, H2S

Carbonate intermediate H2CO3

unstable carbonic acid

Carbonic acid fate

decomposes to H2O and CO2 gas

Redox reaction classification

electron transfer reaction

Oxidation reaction definition

loss of electrons

Reduction reaction definition

gain of electrons

Mnemonic for oxidation and reduction

OIL RIG

OIL RIG meaning

Oxidation Is Loss, Reduction Is Gain

Oxidizing agent definition

accepts electrons, gets reduced

Reducing agent definition

donates electrons, gets oxidized

Half-reactions definition

show separate oxidation and reduction steps

Oxidation number definition

charge atom would have if electrons fully transferred

Oxidation number increase indicates

oxidation

Oxidation number decrease indicates

reduction

Oxidation number rule for free element

0

Oxidation number for alkali metals group1

+1

Oxidation number for alkaline earth metals group2

+2

Oxidation number for hydrogen in compounds

+1

Oxidation number for oxygen in compounds

-2

Sum of oxidation numbers in neutral molecule

0

Sum of oxidation numbers in polyatomic ion

equals net ion charge

Oxidation numbers can be nonintegers example

O2− has O oxidation −1/2

Highest oxidation number group1 or group2 element

equals group number