Reactions in Aqueous Solutions

What is the oxidation number of I^- ?

What is the oxidation number of I^- ?

-1 (ox number has to equal charge on molecule)

Do coefficients affect oxidation numbers?

No

What is the same among all the halogens?

They’re all diatomic

Stock solution

original more concentrated solution (M₁V₁)

Why do ions increase conductivity

ions carry electrical charge from one electrode to the other, completing a circuit

Conductivity and solubility of sugar

It can dissolve in water to create a uniform mixture, but the molecule doesn’t dissociate, so it’s not conductive

Strong acids and bases completely…

dissociate

Strong acids

Hydrochloric acid, HCl Hydrobromic acid, HBr

Hydroiodic acid, HI Chloric acid, HClO3

Perchloric acid, HClO4 Nitric acid, HNO3

Sulfuric acid, H2SO4

Strong bases

Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH)

Heavy group 2A metal hydroxides [Ca(OH)2, Sr(OH)2, Ba(OH2)]

*Most bases are weak*

Acids and bases are either…

weak or strong electrolytes (never nonelectrolytes)

All acids are…

molecular but dissociate in water

Dissolution

to dissolve

Dissociation

breaking up into ions

When NaCl dissolves in water, dissociated sodium ions are said to be…

solvated (surrounded by oxygen atoms in water molecules)

molecular bond

nonmetal + nonmetal or metalloid + nonmetal

ionic bond

metal + nonmetal

Ionic compounds form…

electrolytes in water

Solubility does not equal…

conductivity

Solution

a homogenous mixture of two or more substances

Homogeneous mixtures have a…

constant composition

Aqueous solution

a solution in which water is the dissolving medium (solvent)

Electrolyte

a substance whose aqueous solutions contain ions, and can thus conduct electricity

Nonelectrolyte

not conductive due to no ions in solution

Solvation

process in which a solute is dissolved in a solvent to form a homogeneous mixture; ions dissociate

Ionization

when ions dissociate into their cation and anion

Most molecular compounds are…

nonelectrolytes, except for some acids

Strong electrolytes

solutes that exist in solution completely or nearly all as ions; all water soluble ionic compounds

Weak electrolytes

solutes that exist in solution mostly in the form of neutral molecules with only a small fraction in the form of ions

Weak electrolytic equations have…

double arrows to show chemical equilibrium (strong electrolytes only have 1 arrow)

Precipitate

an insoluble solid formed by a precipitation rxn in solution

Precipitation rxns occur when…

pairs of oppositely charged ions attract each other so strongly that they form an insoluble ionic solid

Solubility

the amount of substance that can be dissolved in a given quantity of solvent at the given temperature

How to predict if a precipitate will form

1. Note the ions present in the reactants

2. Consider the possible cation-anion combos

3. Use solubility rules to determine if any of these combos are insoluble

Precipitation and neutralization rxns

exchange (metathesis) reactions; double replacement

AX + BY → AY + BX

Molecular equation

full chemical formulas w/out indicating ions

Complete ionic equation

soluble, strong electrolytes are separated into ions; rebalance by distributing coefficients and subscripts into ions

Net ionic equation

when spectator ions are omitted from the equation; includes only the ions and molecules directly involved in the rxn

Spectator ions

ions that appear in identical forms on both sides of a complete ionic equation; play no direct role in the rxn

How to write net ionic equations

1. Write a balanced molecular equation

2. Write the complete ionic (only strong electrolytes dissolved in solution are written in ionic form)

3. Identify and cancel spectator ions

Acids

substances that ionize in aqueous solution to form hydrogen ions H+ (aq); because a hydrogen atom consists of a proton and an electron, H+ is simply a proton; acids are proton donors

Monoprotic acids

yield one H+ per molecule of acid (HCl, HNO3)

Diprotic acid

yield two per molec (H2SO4)

Ionization of sulfuric acid occurs…

in two steps:

H2SO4 → H + HSO4

HSO4 ⇌ H + SO4

In acetic acid…

only one H is broken off the oxygen (CH₃COOH)

Bases

• substances that accept (react with) H+ ions. Bases produce hydroxide ions when they dissolve in water. Ionic hydroxide compounds, NaOH, KOH, and CO(OH)2, are the most common.

• Compounds that don’t contain OH can also be bases (ammonia NH3). When added to water ammonia accepts an H+ ion from a water molecule to produce an OH- ion from water.

Examples of strong electrolytes

ionic compounds, strong acids and bases

Examples of weak electrolytes

weak acids and bases

Neutralization rxn

when a soln of an acid and base are mixed to form water and a salt

Salt

any ionic compound whose cation comes from a base and whose anion comes from an acid

Main feature of any neutralization rxn

H+ and OH- combine to form H2O

Oxidation

when an atom, ion, or molecule becomes more positively charged, loss of electrons

Reduction

when an atom, ion, or molecule becomes more negatively charged, gain of electrons

Oxidation of metals by acids and salts

Displacement rxn; single replacement

A + BX → AX + B

Activity series

list of metals arranged in order of decreasing ease of oxidation

Active metals

The metals at the top (alkaline earth metals) are most easily oxidized; meaning, they react most readily to form compounds

Noble metals

The metals at the bottom (transition elements from groups 8B and 1B), are very stable and form compounds less readily

Any metal on the list can be oxidized by the ions of the elements…

below it

Higher element in series =

element that’s oxidized (loses electrons; increased ox #)

Concentration

• the amount of solute dissolved in a given quantity of solvent or quantity of solution. The greater the amount of solute dissolved in a certain amount of solvent, the more concentrated the solution is.

• Measured in molarity (number of moles of solute/liter of soln)

Molarity =

moles of solute / volume of solution in Liters

m = n/v

A 1 molar solution (1 M) contains…

1 mol of solute per liter of soln

The concentration of a dissociated ion is the same as its salt if the subscript is…

1 (if it’s anything greater multiply the subscript by the molarity of the whole molecule)

A 1.0 M soln of Na₂SO₄ is ___ in Na⁺ ions and ___ in SO₄²⁻ ions

2 M; 1 M

Molarity is a conversion factor between…

volume of soln and moles of solute

Dilution

When solutions of a lower concentration are obtained by adding water

Dilution equation

M (conc) x V (conc) = M (dil) x V (dil)

Titration

combining a solution where the solute concentration is not known with a reagent solution of known concentration, called the standard solution. Just enough standard soln is added to completely react w the solute in the soln of unknown conc.

Equivalence point

the point at which stoichiometrically equivalent quantities are brought together.

Nonmetals want to…

gain electrons (least likely to be oxidized)

In complete ionic equations, only ionize…

aqueous substances (do NOT ionize g, l, or s)

In neutralization reactions, do not ionize…

water, and the salt if it’s insoluble

In order for a single replacement reaction to work, the metal doing the replacing must be…

higher up on the activity series