Chapter 4 Chemistry Review

Aqueous Reactions and Solution Stoichiometry

By: Enid Truong and Alyisha Bouges

Electrolytes

A substance whose aqueous solution contains ions. The more ions present the stronger the solution. Ex:NaCl

Nonelectrolyte: a substance that does not form ions Ex: C12H22O11

Strong vs. Weak

• Strong = completely ionized, all Ionic compounds and the strong molecular acids

• Weak = some amount ionizes, weak acids and bases

Electrolytes

Dissolution?

When an ionic compound dissolves in water.

Solvation?

When water molecules surround an ion to stop them from rebonding.Denoted with an aqueous phase abbreviation: (aq)

Precipitates

A reaction that results in the formation of an insoluble product are called Precipitation Reactions.

A precipitate is an insoluble solid that is formed in a reaction

Ex:KI (aq) + Pb(NO3)2 (aq) ---> PbI2 (s) + 2KNO3 (aq)

Solubility Rules!

Which of the pair is insoluble (will be solid)?

• Na2SO4 or BaS

• KOH or CaCl2

• MgCrO4 or LiClO3

Solubility Rules!

Net Ionics

CaCl2 (aq) + Na2CO3 (aq) ---> CaCO3 (s) + 2NaCl (aq)

Write the net ionic and find the precipitation reaction that occurs when aqueous solutions of Calcium Chloride and Sodium Carbonate are mixed.(as seen above)

Ca^2+(aq) + CO3^2+(aq) ------> CaCO3(s)

Acids vs. Bases

Acids:

• H+

• Proton donor

• Ex: HCl(monoprotic)H2SO4(diprotic)H3P(triprotic)Bases:

• OH-

• Proton acceptor

• Ex: Al(OH)3

Strong acids and bases are strong electrolytes, so they ionizes completely. Weak acids and bases do not.

Acids vs. Bases

Ways to remember:

Our favorite for strong acids: http://www.youtube.com/watch?v=jPilrd7b1B8

Something new for strong bases: The Thumb Rule

(AKA: The Rule of Thumb)

Neutralization Reactions

When you add an acid to a base, the result is water and a salt.

Ex: HCl (aq) + NaOH (aq) ---> H2O (l) + NaCl (aq)

Try one!! Magnesium hydroxide and hydrochloric acid. What do they form?

H2O(l) + MgCl2(aq)

Acid-Base Gas FormationsSulfide ion and Carbonate ions both from

gas when they react with acids. For example:

2HCl(aq) + Na2S(aq) --->H2S(g) + 2NaCl(aq)

But what does this produce?Na2SO3(aq) + HCl(aq)----> ?

NaCl(aq) + H2SO4

H2O(l) + SO2(g)

Oxidation-Reduction

AKA :REDOX Reactions

Oxidation - the LOSS of electrons by a substance.Reduction - the GAIN of electrons by a substanceGreat way to memorize this: LEO says GER (Lose

Electron Oxidizes/ Gains Electrons Reduces)

Which one reduces and which one oxidizes? :

Ca(s) + 2 H^+(aq) ---> Ca2^+(aq) + H2(g)

oxidized!

Reduced!

Oxidation Numbers

1) For an Atom in its elemental form, the oxidation number is always zero

EX: H2 has an oxidation number of 0

2) For any Monatomic ion the oxidation number equals the charge on the ion

EX: K+ has an oxidation number of +1 and S2- has an oxidation number of -2

Oxidation Numbers

3) Nonmetals usually have negative oxidation numbers, but they can be positive with some exceptions:

1) The oxidation number of oxygen is usually -2 in both ionic and molecular compounds. The exception is in peroxides (O2)^2-, giving each oxygen a charge of 1-.

For ex: BaO2 ; (1)(-2) + (2)(x) = 0 ; O = -1

2) The oxidation of Hydrogen is usually +1 when bonded to nonmetals and -1 with metals

For ex: NaH ; Na is a metal, so in this case, the ox. number of H is -1

Oxidation Numbers

3) The oxidation number of fluorine is -1 in all compounds. Other halogens have an ox. number of 1- in most binary compounds, but when combined with oxygen, they have positive ox. numbers.

4) The sum of the oxidation numbers of all atoms in a neutral compound is zero. The sum of the ox. number of polyatomic ions equals the charge of the ion.

For ex: (Cr2O7)^ -2 Cr is unknown, but we know O has an oxidation number of -2, so (x)(2) + (-2)(7) = -2. Cr = -1

Molarity

Molarity (M) = Moles solution / volume of solution in liters

Problem: What is the molar concentration of K+ ions in a o.o15M solution of potassium carbonate?

0.030M

Dilution and Titration

McVc = MdVd (where c = concentrate & d = dilute)

Titration: a method scientists often use to determine the concentration of a particular solute in a solution..

MaVaIa = MbVbIb (M stands for molarity, V stands for volume, I stand for ions, a = acids and b = base) To find "I" look at the amount of H+ and OH- ions

Activity Series

Take out your Super Secret Periodic Tables and turn to page 39.

This is your table of the activity series.Which is a list of metals arranged in

order of decreasing ease of oxidation and to form compounds.

Any metal on the list can be oxidized by the element below it!

Activity Series

Now answer this:

If you add copper to a solution with silver present, will there be a reaction?

Yes!

Now what if gold were added to the same solution?

No!