CHAPTER 4: Aqueous Reactions and Solution Stoichiometry (4.1 - 4.4)

Question 1

DISSOCIATION

Answer 1

When an ionic substance dissolves in water, the solvent separates (suspended in solute) into the individual ions from the crystal.

IE.
KCL (aq) = K+ (aq) + Cl- (aq)
CuSO4 (aq) = Cu^2+ (aq) + SO4^2-

Question 2

Electrolytes

Answer 2

A substance that dissociates into ions when dissolved in water (conducts electricity)

Question 3

NONelectrolytes

Answer 3

Nonelectrolytes may dissolve in water, but they do not dissociate into ions when they do.
- Molecular compounds tend to be nonelectrolytes, except for acids and bases.

Question 4

Electrolytes’ Strength

Answer 4

STRONG ELECTROLYTE:
Dissociates completely when dissolved in water
- IONIC (all that are soluble in H20 (l)
- MOLECULAR: Strong acids (7)

WEAK ELECTROLYTE:
Dissociates only partially when dissolved in water
- IONIC: NONE
- MOLECULAR: Weak acids + bases

NONELECTROLYTE:
All other compounds

Question 5

STRONG ACIDS (7)

Answer 5

HCl (hydrochloric)
HBr (hydrobromic)
HI (hydroiodic)
H2SO4 (sulfuric)
HNO3 (nitric)
HClO3 (chloric)
HClO4 (perchloric)

Question 6

SOLUBILITY / PRECIPITATION REACTION

Answer 6

• If a compound is insoluble in water, it forms a solid.
• If NO SOLID (precipitate) is formed, then NO REACTION occurred.

Ex. Precipitation reaction:
KI (aq) + AgNO3 (aq) –> KNO3 (aq) + AgI (s)

Question 7

IONIC EQUATIONS

Answer 7

There are three types of equations used to describe reactions in AQUEOUS SOLUTIONS:

1. MOLECULAR EQUATION: Shows all formulas.
2. COMPLETE IONIC EQUATION: Shows all compounds as they actually exist (ie. as ions in aqueous solution)
3. NET IONIC EQUATION: Show only those ions that undergo a change (SPECTATOR IONS, or ions that aren’t involved, are removed/cancelled)

Question 8

MOLECULAR EQUATION EX.

Answer 8

2AgNO3 (aq) + Na2CrO4 (aq) –> Ag2CrO4 (s) + 2NaNO3 (aq)

Question 9

IONIC EQUATION EX.

Answer 9

2Ag^+ (aq) + 2NO3^- (aq) + 2Na^+ (aq) + CrO4^2- (aq) –> Ag2CrO4 (s) + 2Na^+ (aq) + 2NO3^- (aq)

Question 10

NET IONIC EQUATION EX.

Answer 10

2Ag^+ (aq) + CrO4^2- (aq) –> Ag2CrO4 (s)

Question 11

NEUTRALIZATION REACTION

Answer 11

Generally, when solutions of an acid and a base are combined, the products are a salt and water.

Question 12

When a strong acid reacts with a strong base…

Answer 12

Ex.
HCl (aq) + NaOH (aq) –> NaCl (aq) + H20 (l)

–> The NET IONIC EQUATION is:
H^+ (aq) + OH^- (aq) –> H20 (l)

Question 13

***GAS FORMING REACTIONS*** 
Acids that (spontaneously) decompose

Answer 13

When certain acids that spontaneously decompose, a gas(es) forms.

• H2CO3 (aq) –> H2O (l) + CO2 (g)
• H2SO3 (aq) –> H2O (l) + SO2 (g)
• NH4OH (aq) –> H2O (l) + NH3 (g)

Question 14

GAS FORMING REACTIONS

Carbonates (CO3^2-) and Bicarbonates (HCO3^-) with acids

Answer 14

Carbonates and bicarbonates, when combined with acids, produce H2CO3 –> H2O (l) + CO2 (g)

Ex.
CaCO3 (aq) + HCl (aq) –> CaCl2 (aq) + CO2 (g) + H2O (l)
NaHCO3 (aq) + HBR (aq) –> NaBr (aq) + CO2 (g) + H2O (l)

THINK OF THE WAY BAKING SODA FIZZES WHEN COMBINED WITH ACETIC ACID (vinegar) or CITRIC ACID (lemon juice)
–> Fizzes and bubbles until reaction is complete and a liquid (H20 (l) + whatever) is leftover

Question 15

GAS FORMING REACTIONS

Hydrogen sulfide

Answer 15

Hydrogen sulfide (H2S) has a low solubility in water; therefore, reactions that produce it will form a gas (smells like sulfur)

Ex.
Na2S (aq) + H2SO4 (aq) –> Na2SO4 (aq) + H2S (g)

Question 16

GAS FORMING REACTIONS

Ammonium salt + a strong base

Answer 16

When an ammonium salt combines with a strong base, NH4OH is formed; however, it decomposes into H2O (l) + NH3 (g)

Ex.
NH4Cl (aq) + NaOH (aq) –> H2O (l) + NH3 (g) + NaCl (aq)

Question 17

OXIDATION - REDUCTION REACTIONS (Redox)

Answer 17

• Oxidation and reduction always occur together.

OXIDATION: when an atom or ion LOSES ELECTRON(s)
REDUCTION: when an atom or ion GAINS ELECTRON(s)

Ex. Combustion reactions and corrosion [reactions] (rusting of metals)

Question 18

REDOX REACTIONS:

OXIDATION NUMBERS

Answer 18

Oxidation Numbers:

• ELEMENTS in natural elemental state = 0 (ex. C (s) = 0)
• MONATOMIC ION = its charge (ex. Na^- = -1)
• OXYGEN = -2, except in the peroxide ion (O2^-2), where its oxidation number is -1
• HYDROGEN = +1 when bonded to a nonmetal; -1 when bonded to a metal
• FLUORINE = (always) -1
• Other Halogens: = -1 when they are negative (they can have a positive oxidation no., typically in oxyanions)

SUM OF OXIDATION NUMBERS IN A NEUTRAL COMPOUND = 0
SUM OF OXIDATION NUMBERS IN A POLYATOMIC ION = charge on the ion

Question 19

Oxidized vs. Reduced & Oxidizing / Reducing Agents

Answer 19

Oxidized element: the ELEMENT that LOSES ELECTRON(S)
Reduced element: the ELEMENT that GAINS ELECTRON(S)

Oxidizing agent: ENTIRE COMPOUND (containing element that was reduced) that causes the OXIDIZED element to lose electrons

Reducing agent: ENTIRE COMPOUND (containing element that was oxidized) that causes the REDUCED element to lose electrons