CHAPTER 6B AND 7 CHEM 110

Molarity (M) - definition

Moles of solute per liter of SOLUTION (not solvent). Units are mol/L.

Molarity formula

M = mol / L

Formula for moles, from molarity

mol = M x L

Formula for liters, from molarity

L = mol / M

Solute vs. solvent

Solute is the substance that gets dissolved. Solvent is the liquid that dissolves it.

Why does molarity use SOLUTION volume, not solvent volume?

The dissolved solid takes up space of its own, so the total volume is more than the water you added.

What does 0.37 M NaOH mean?

0.37 mol of NaOH dissolved in 1 liter of solution.

Dilute vs. concentrated

Dilute = low concentration of solute. Concentrated = high concentration of solute.

Dilution formula

M1V1 = M2V2 (1 = concentrated stock, 2 = dilute final solution)

When can you use M1V1 = M2V2?

ONLY for dilution - adding solvent to a solution that already exists. Never for making a solution from a solid.

Why does the dilution formula work?

Adding water does not change the number of moles of solute. Only the volume changes.

Do volumes have to be in liters for the dilution formula?

No. Volume appears on both sides so the units cancel. Just use the same unit on both sides.

Steps to prepare a solution from a solid

Weigh the solid, put it in a volumetric flask, add water and dissolve it, fill to the etched mark, cap and invert to mix.

Why fill to the mark instead of adding a measured amount of water?

Molarity is moles per liter of solution. Filling to the mark is what makes the final volume exact.

Volumetric flask

A flask calibrated to one exact volume, marked by an etched line on the neck.

Diluting a concentrated acid - what goes in first?

Water first, then add the acid to it. Diluting acid gives off heat and can spit back.

How do you know a problem is a dilution problem?

It mentions a stock solution, or says to dilute, or gives you a more concentrated solution to start from.

Does a dilution problem need a molar mass?

No. If you are reaching for the periodic table on a dilution problem, you picked the wrong formula.

Electrolyte

A compound that conducts electricity when dissolved in water, because it forms ions that are free to move.

Strong electrolyte

Completely dissociates into ions in water.

Weak electrolyte

Only partially dissociates. Exists in solution mostly as whole molecules.

Nonelectrolyte

Dissolves in water but does not form ions at all.

Which substances are strong electrolytes?

Soluble salts, the six strong acids, and the six strong bases.

Which substances are weak electrolytes?

Ammonia and other nitrogen compounds, and every acid except the six strong acids.

Example of a nonelectrolyte

Sugar (C12H22O11). It dissolves completely but stays neutral, so nothing carries a charge.

Single arrow vs. double arrow in an equation

Single arrow = complete dissociation (strong). Double arrow = partial and reversible (weak).

Solubility vs. dissociation

Solubility is HOW MUCH dissolves. Dissociation is how COMPLETELY the dissolved part breaks into ions. They are separate questions.

Acetic acid - soluble? what kind of electrolyte?

Very soluble, but a WEAK electrolyte. Only about 1% dissociates.

Ba(OH)2 - soluble? what kind of electrolyte?

Not very soluble, but a STRONG electrolyte. Whatever does dissolve dissociates completely.

Are all acids soluble in water?

Yes. Every acid, strong or weak, is soluble.

Four types of ionic compounds in this course

Acids, hydroxides (bases), metal oxides, and salts.

What is a salt?

The product of an acid-base neutralization reaction.

Why can ions conduct electricity?

They carry a charge and are free to move, so they can carry a current. Cations move to the negative electrode, anions to the positive.

The six strong acids

HCl, HBr, HI, HNO3, H2SO4, HClO4

Structure of the strong acid list

Three hydrohalic acids (HCl, HBr, HI) plus three oxoacids (HNO3, H2SO4, HClO4).

Which hydrohalic acid is NOT strong?

HF, hydrofluoric acid. It is weak - fluorine is the odd one out.

Is any acid not on the six-acid list strong?

No. By this course's rule, every acid that is not one of the six is weak.

The six strong bases

LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

Structure of the strong base list

Group 1A hydroxides (Li, Na, K) plus the bottom three of Group 2A (Ca, Sr, Ba).

Mg(OH)2 - strong or weak base?

Weak. Magnesium sits too high in Group 2A to make the strong list.

Al(OH)3 - strong or weak? soluble?

Weak base, and insoluble.

NH3 - acid or base? strong or weak?

Weak base. Nitrogen-containing compounds act as weak bases.

Which strong bases are NOT required for this course?

RbOH, CsOH, FrOH, and Tl(OH)3.

Solubility Rule 1

Group 1A (Li+, Na+, K+, Cs+) and ammonium (NH4+) compounds are SOLUBLE. No exceptions.

Solubility Rule 2

Acetates, perchlorates, and nitrates are SOLUBLE. No exceptions.

Solubility Rule 3

Most chlorides, bromides, and iodides are SOLUBLE. Exceptions: Ag+, Hg2 2+, Hg2+, Pb2+.

Solubility Rule 4

Most sulfates are SOLUBLE. Exceptions: Ca2+, Sr2+, Ba2+, Ag+, Hg2 2+, Hg2+, Pb2+.

Solubility Rule 5

Most carbonates and phosphates are INSOLUBLE. Exceptions: Group 1A and NH4+.

Solubility Rule 6

Most sulfides and hydroxides are INSOLUBLE. Exceptions: Group 1A, NH4+, Ca2+, Sr2+, Ba2+.

Which solubility rules have no exceptions?

Rules 1 and 2.

Which solubility rules start from INSOLUBLE?

Rules 5 and 6. Carbonates and phosphates, sulfides and hydroxides.

Exception trio for Rules 3 and 4

Silver, mercury, and lead: Ag+, Hg2 2+, Hg2+, Pb2+.

Exception trio for Rules 4 and 6

Calcium, strontium, barium: Ca2+, Sr2+, Ba2+.

Do you check the cation or the anion first?

The anion. It tells you which rule applies. Then check whether the cation is on that rule's exception list.

AgBr - soluble or insoluble?

Insoluble. Rule 3 - silver is an exception.

Ca(NO3)2 - soluble or insoluble?

Soluble. Rule 2 - nitrates have no exceptions, so the cation does not matter.

CaSO4 - soluble or insoluble?

Insoluble. Rule 4 - calcium is an exception.

Al(OH)3 - soluble or insoluble?

Insoluble. Rule 6 - aluminum is not on the exception list.

Mg3(PO4)2 - soluble or insoluble?

Insoluble. Rule 5 - magnesium is not Group 1A or ammonium.

BaCO3 - soluble or insoluble?

Insoluble. Rule 5 - barium is not Group 1A or ammonium.

K2CO3 - soluble or insoluble?

Soluble. Rule 5 exception - potassium is Group 1A.

PbSO4 - soluble or insoluble?

Insoluble. Rule 4 - lead is an exception.

(NH4)3PO4 - soluble or insoluble?

Soluble. Rule 5 exception - ammonium.

Fe(ClO4)3 - soluble or insoluble?

Soluble. Rule 2 - perchlorates have no exceptions.

Molecular equation

Written as if every reactant and product is a whole neutral compound, even if it actually exists as ions.

Complete ionic equation

Strong electrolytes written as separate ions. Everything else stays whole.

Net ionic equation

The complete ionic equation with the spectator ions removed.

Spectator ion

An ion that appears unchanged on both sides of the equation and takes no part in the reaction.

What gets split into ions in a complete ionic equation?

Only soluble ionic compounds and the six strong acids.

What stays whole in a complete ionic equation?

Weak acids, weak bases, insoluble solids, pure liquids, and gases.

Precipitation reaction

Two solutions are mixed and an insoluble compound forms, falling out of solution as a solid.

Precipitate

The insoluble solid that forms in a precipitation reaction.

Other names for a precipitation reaction

Exchange reaction, or metathesis reaction.

How do you find the possible products of an exchange reaction?

Swap the cations and anions between the two reactants.

What if both possible products are soluble?

No reaction occurs.

Three reaction types in Chapter 7

Precipitation, acid-base, and oxidation-reduction (redox).

Do you balance before or after writing the ionic equations?

Balance the molecular equation first, then expand it into the ionic forms.

Binary acid

Hydrogen plus one other element, with no oxygen. Example: HCl.

Oxoacid

Contains hydrogen, oxygen, and one other element. Example: HNO3.

Carboxylic acid

An acid made of hydrogen plus an organic molecule with a carboxylate group, RCOOH. Example: CH3COOH.

Naming rule for a binary acid

hydro- + root + -ic acid. Cl- becomes hydrochloric acid.

Anion ending in -ite becomes which acid?

-ous acid. Chlorite becomes chlorous acid.

Anion ending in -ate becomes which acid?

-ic acid. Chlorate becomes chloric acid.

Anion ending in -ide becomes which acid?

hydro- + root + -ic acid. Bromide becomes hydrobromic acid.

Sulfate as an acid

H2SO4, sulfuric acid. Note the extra -ur- added for sulfur.

Phosphate as an acid

H3PO4, phosphoric acid. Note the extra -or- added for phosphorus.

Name HClO3

Chloric acid, from chlorate.

Name HBrO4

Perbromic acid, from perbromate.

Formula for hydrobromic acid

HBr. The prefix hydro- tells you there is no oxygen.

Formula for chlorous acid

HClO2. The -ous ending means it comes from the -ite anion, chlorite.

Formula for sulfurous acid

H2SO3, from sulfite.

How do you build an acid from an anion?

Add enough H+ ions to make the whole compound neutral.

Acid anion

An anion made by adding H+ to an oxoanion. Named with hydrogen-, monohydrogen-, or dihydrogen-.

Name HSO4-

Hydrogen sulfate.

Names of HPO4 2- and H2PO4-

Monohydrogen phosphate and dihydrogen phosphate.

Acid-base indicator

A dye that changes the color of a solution depending on how much acid or base is present.

Arrhenius acid

A substance that produces hydrogen ions (H+) when dissolved in water.

Arrhenius base

A substance that produces hydroxide ions (OH-) when dissolved in water.

Bronsted-Lowry acid

A proton donor. It gives away an H+.

Bronsted-Lowry base

A proton acceptor. It takes an H+.