chem 200/202
TRANSCRIPT
CHEM 200/202
Professor Byron W. Purse
Office: virtual only this semester
All course-related emails are to be sent to:
My office hours will be held on Zoom on
Monday from 3:00 to 5:00 PM. Appointments
can be made for special issues, but not one-
on-one tutoring.
ANNOUNCEMENTS
• Exam 1 starts 3:00 pm Friday, September 17th and will close at 3:00 pm
Saturday, September 18th
• OWL Assignments for Chapter 1 - 4: Chapter Problem Sets & Chapter
Assessments due Thursday, September 16th at 11:59 pm
• Due Sunday, Sep 19th at 11:59 PM
• Pre-Lab: Limiting Reagents(Canvas)
• Pre-Assignment: Limiting Reagenets(OWL Labs)
• Lab Report: Qualitative Analysis (Canvas)
• SIM: Qualitative Analysis of Group I Cations (Hayden McNeil)
CHAPTER 4
STOICHIOMETRY OF
CHEMICAL REACTIONS
REACTION
CLASSIFICATIONS• There are three principle aqueous
chemical reactions that we will focus on
in this course:
• Precipitation reactions (solid formation)
• Acid-Base reactions (neutralization)
• Redox reactions (oxidation-reduction)
EQUATIONS FOR AQUEOUS
IONIC REACTIONS• Molecular equation: shows all the reactants and
products as intact, undissociated compounds (sometimes
we will be required to balance the chemical equation
first).
• Ionic equation: shows all the soluble ionic substances
dissociated into ions.
• Net ionic equation: eliminates the spectator ions and
shows the actual chemical change that takes place.
NET IONIC EQUATIONS
• Steps:
• Write the balanced molecular equation - you may
have to predict the products of the reaction.
• Ionize all strong electrolytes in solution.
• Cancel all spectator ions.
• Write the leftover species.
PRECIPITATION
REACTIONS• Precipitation reactions occur when pairs of insoluble ions
(e.g. Ag+ and Cl-) both present in solution at the same time.
• A mixture of aqueous solutions may result in more than
one precipitate being formed, if more than one insoluble
pair is present.
• Knowledge of the common soluble and insoluble ions is
required to predict precipitations (The Solubility Rules).
• Write the leftover species.
SOLUBILITY RULES
1. All common compounds of Group 1A(1) ions (Li+, Na+, K+...) and
ammonium ions (NH4+)
2. All common nitrates (NO3-), acetates (CH3CO2
-) and most
perchlorates (ClO4-)
3. All common chlorides (Cl-), bromides (Br-) and iodides (I-);
except those of Ag+, Pb2+, Cu+ and Hg22+. All common fluorides
(F-) are soluble; except for Pb2+ & Group2A(2)
4. All common sulfates (SO42-); except Ca2+, Sr2+, Ba2+, Ag+ & Pb2+
Soluble
SOLUBILITY RULES
1) All common metal hydroxides are insoluble; except
those of Group 1A(1) and the larger members of
Group 2A(2) - beginning with Ca2+.
2) All common carbonates (CO32-), phosphates (PO4
3-)
and chromates (CrO42-) are insoluble; except those
from Group 1A(1) and ammonium (NH4+).
3) All common sulfides (S2-) are insoluble; except
those of Groups 1A(1), 2(A)2 and NH4+.
Insoluble
SOLUBILITY RULES FOR EXAMS
See Canvas:
PREDICTING
PRECIPITATION
1. Note the ions present in the reactants.
2. Consider the possible cation-anion combination.
3. Decide whether any of the ion combinations is
insoluble and thus, form a precipitate.
PROBLEM
•Balance the reaction below and provide
the ionic and net ionic equation for the
reaction. Does a precipitate form?
_Fe(NO3)3(aq) + _Na2CO3(aq) → _Fe2(CO3)3 + _NaNO3
PREDICTIONWhat happens when you mix a solution of lead nitrate
reacting with a solution of potassium iodide? Write the
balanced equation, ionic equation, and net ionic equation.
UPCOMING KAHOOTWhich common substance has the following elemental
composition?
5.04% H
35.00% N
59.59% O
ACIDS AND BASES
• (Brønsted) Acids - produce H+(aq) when dissolved in
water
• (Brønsted) Bases - produce OH-(aq) when dissolved in
water
• Strong acid/base - completely dissociates in water
• Weak acid/base - incompletely dissociates in water
ACID BASE THEORY• H+ (proton) forms H3O+ (hydronium ion) in water
• H+ is electron deficient, wants electrons, electron pair acceptor
• OH- is electron rich, can donate a pair of electrons
Water self-ionizes: 2H2O(l) → H3O+(aq) + OH-
(aq)
Acid-Base definitions:Arrhenius:
•Acid increases conc. of H3O+ when added to water
•Base increases conc. of OH- when added to waterBrønsted-Lowry:
•Acid = proton donor
•Base = proton
acceptor
Lewis:
•Acid: electron pair acceptor
•Base: electron pair donor
ACID-BASE THEORY• Arrhenius example: NaOH (aq) + HCl (aq) → H2O(l) + NaCl(aq)
• Net ionic equation for all Arrhenius acid-base reactions:
H+(aq) + OH-
(aq) → H2O(l)
• Brønstead example: HCl(benzene) + NH3(benzene) → NH4Cl(s)
• HCl donates a proton to NH3
• Lewis example: NH3(g) + BH3(g) → NH3BH3
• NH3 donates an electron pair to BH3
SELECTED ACIDS & BASES
Strong Acids
Hydrochloric acid, HCl
Hydrobromic acid, HBr
Hydroiodic acid, HI
Nitric acid, HNO3
Sulfuric acid, H2SO4
Perchloric acid, HClO4
Strong Bases
Sodium hydroxide, NaOH
Potassium hydroxide, KOH
Calcium hydroxide, Ca(OH)2
Strontium hydroxide, Sr(OH)2
Barium hydroxide, Ba(OH)2
Weak Acids
Hydrofluoric acid, HF
Phosphoric acid, H3PO4
Acetic acid, CH3COOH (or
HC2H3O2)
Weak Bases
Ammonia, NH3
ACIDS• Monoprotic: one ionizable hydrogen
• HCl + H2O → H3O+ + Cl-
• Diprotic: two ionizable hydrogens
• H2SO4 + H2O → H3O+ + HSO4-
• HSO4- + H2O → H3O+ + SO4
2-
• Triprotic: three ionizable hydrogens
• H3PO4 + H2O → H3O+ + H2PO4-
• H2PO4- + H2O → H3O+ + HPO4
2-
• HPO42- + H2O → H3O+ + PO4
3-
Polyprotic, generic
term meaning that
there is more than
one ionizable
hydrogen on the
molecule.
BASES
• Monobasic: yields one OH- ion
• KOH → K+ + OH-
• NH3 +H2O → NH4+ + OH-
• Dibasic: yields two OH- ions
• Ba(OH)2 → Ba2+ + 2OH-
• Ca(OH)2 → Ca2+ + 2OH-
ACID-BASE NEUTRALIZATION
Acid + Base → Water + SaltMolecular
equation
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
Total ionic
equationH+
(aq) + Cl-(aq) + Na+(aq) + OH-
(aq) → H2O(l) + Na+(aq) + Cl-(aq)
Net ionic
equationH+
(aq) + OH-(aq) → H2O(l)
Hint: Balance the H+ with OH- the rest will work itself out.
AN AQUEOUS STRONG ACID-BASE
REACTION ON THE ATOMIC SCALE
ACID-BASE TITRATION
QUESTIONA 20.00 mL solution of phosphoric acid is titrated
(neutralized) with 14.85 mL of a 1.205 M barium hydroxide
solution. From this information determine the concentration
of the phosphoric acid solution. Does a precipitate form?
SOLUBILITY RULES
1) All common metal hydroxides are insoluble; except
those of Group 1A(1) and the larger members of
Group 2A(2) - beginning with Ca2+.
2) All common carbonates (CO32-), phosphates (PO4
3-)
and chromates (CrO42-) are insoluble; except those
from Group 1A(1) and ammonium (NH4+).
3) All common sulfides (S2-) are insoluble; except
those of Groups 1A(1), 2(A)2 and NH4+.
Insoluble
QUESTIONWhat is the concentration of a sulfuric acid solution if it
requires 26.05 mL of a 2.045 M sodium hydroxide solution
to titrate 12.05 mL of the sulfuric acid solution?
REDOX REACTIONS
OXIDATION NUMBER RULES
General Rules1. For an atom in its elemental form (e.g. Na, O2, Cl2,...) the O.N. = 0.
2. For a monoatomic ion (e.g. Br-, Cu2+,...) the O.N. = ion charge.
3. The sum of the O.N. values for atoms in a compound equals zero. For
polyatomic ions the sum equals the charge of the ion.
Specific Rules
1. For Group 1(A)1 - O.N. is +1 in all compounds
2. For Group 2(A)2 - O.N. is +2 in all compounds
3. For hydrogen - O.N. is +1 when bound to nonmetals (-1 with metals)
4. For fluorine - O.N. is -1 when bound to metals & boron
5. For oxygen - O.N. is -1 when in peroxides (e.g. H2O2)
- O.N. is -2 for all others (except with fluorine)
6. For Group 7(A)17 - O.N. is -1 when with metals, nonmetals
(except O) & for other halogens lower in group
OXIDATION NUMBERSThe main group elements can have
different oxidation numbers depending
on the molecule they are part of.
CompoundO.N. of
nitrogen
NH3 -3
N2H4 -2
NH2OH -1
N2 0
N2O +1
NO +2
NO2- +3
NO2 +4
NO3- +5
ASSIGNING OXIDATION
NUMBERS(a) H2S
(b) SO32-
(c) Na2SO4
(d) KNO3
(e) AlH3
(f) NH4+
(g) H2PO4-
Balance this equation and assign oxidation
numbers
REDOX REACTION IN
COMPOUND FORMATIONElectrons are
transferred in the
formation of ionic
compounds.
Electrons are
shifted in the
formation of
covalent
compounds.
REDOX REACTIONS
REDOX TERMINOLOGY
• Mg loses electrons
• Mg is oxidized
• Mg is the reducing agent
• The oxidation number of
Mg is increased
2Mg(s) + O2(g) → 2MgO(s)
2Mg → 2Mg2+ + 4e- O2 + 4e- → 2O2-
• O gains electrons
• O is reduced
• O is the oxidizing agent
• The oxidation number
of O is decreased
O.N.: 0 +2 O.N.: 0 -2
OXIDATION REDUCTION
OIL RIG
Oxidation
is
loss of electrons
Reduction
is
gain of electrons
LEO GER
Lose
electrons is
oxidation
Gain
electrons is
reduction
QUESTION
What is the oxidation number of carbon in Na2C2O4?
Oxidation number:
0
+1
+2
+3
+4
QUESTIONIdentify the oxidizing agent and reducing
agent in the following reaction:
Sn(s) + 2H+(aq) → Sn2+
(aq) + H2(g)
Oxidizing
agent
Reducing
agentAnswer
H+ Sn A
H+ Sn2+ B
Sn H+ C
Sn H2 D
Sn2+ H2 E
TYPES OF REDOX
REACTIONS• The different types of redox reactions are classified by the
components of the reaction and what happens to those
components.
• There are four types of redox reactions which involve
elements - combination, decomposition, displacement
and combustion.
• In these reactions, elements may be reagents, products or
transferred during the reaction.
COMBINATION REACTION2K(s) + Cl2(g) → 2KCl(s)
2NO(g) + O2(g) → 2NO2(g)
DECOMPOSITION REACTION
2HgO(s) → 2Hg(l) + O2(g)∆
∆ = heat
2H2O(l)electricity
2H2(g) + O2(g)
DISPLACEMENT REACTIONAn active metal displacing
hydrogen from water2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
DISPLACEMENT REACTIONSDisplacing one metal by another metal
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
More
reactive
Less
reactive
Zn Cu
Write the redox equations to explain how this
lemon battery generates a current and 0.906 V.
COMBUSTION REACTIONS
•Combustion reactions always involve oxygen.
•The reactions reduce oxygen and release
energy, frequently as heat and light.
2CO(g) + O2(g) → 2CO2(g)
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
C6H12O6(g) + 6O2(g) → 6CO2(g) + 6H2O(g)
REACTION YIELDS
• The reaction yield is a measure of the completeness of a
reaction; quantifying how much of the possible product
was formed.
• Determining the theoretical yield for a reaction requires a
balanced chemical reaction, and the identification of the
limiting reagent.
• The limiting reagent is the reagent that will be entirely
consumed first, stoping the reaction (limiting the amount
of product formed).
LIMITING REAGENT
• The Haber-Bosch process produces ammonia from
nitrogen and hydrogen gas (unbalanced reaction
below).
• _N2(g) + _H2(g) → _NH3(g)
• Hydrogen limiting reagent: How many grams of
ammonia would be produced if 4.04 g of H2 and an
infinite amount of N2? How much N2 is consumed?
• The Haber-Bosch process produces ammonia from nitrogen and hydrogen gas (unbalanced reaction below).
• _N2(g) + _H2(g) → _NH3(g)
• Hydrogen limiting reagent: How many grams of ammonia would be produced if 4.04 g of H2 and an infinite amount of N2?
How much N2 is consumed?
REACTION YIELDS
• Not every reaction proceeds perfectly to produce 100% of the maximum product.
• Reactions that are imperfect have reaction yields of less than 100%.
• Considering the reaction: _N2(g) + _H2(g) → _NH3(g)
• The reaction was performed with 4.04 g of H2 and excess N2. At the end of the
reaction your yield is only 15.0%. What mass of NH3 is formed?
• If the reaction produced 7.24 g NH3. What would the yield be?
LIMITING REAGENT
PROBLEM
• What is the limiting reagent when 2.00 g of
Si and 1.50 g of N2 is reacted? How many
moles of Si3N4 will be produced? Be sure to
balance the equation first.
_Si(s) + _N2(g) → _Si3N4(s)
LIMITING REAGENT
PROBLEM• What is the limiting reagent when 2.00 g of Si and 1.50 g of N2 is reacted? How
many moles of Si3N4 will be produced? Be sure to balance the equation first.
_Si(s) + _N2(g) → _Si3N4(s)
QUESTIONIdentify the oxidizing agent and reducing
agent in the following reaction:
Sn(s) + 2H+(aq) → Sn2+
(aq) + H2(g)
Oxidizing
agent
Reducing
agentAnswer
H+ Sn A
H+ Sn2+ B
Sn H+ C
Sn H2 D
Sn2+ H2 E
• An aqueous solution of H2SO4 is added to an aqueous solution of
Ba(OH)2. The reaction is monitored using a conductivity meter.
Predict the correct statement(s):
1. Both H2SO4 & Ba(OH)2 are strong electrolytes
2. This is a neutralization reaction
3. This is a precipitation reaction
4. The light bulb will glow at the neutralization point
•Statement 2
•Statements 1 & 2
•Statements 1, 2 & 3
•All of the statements are true
•All of the statements are lies
Answers
A
B
C
D
E
