Lecture 9OWL ONLINE HOMEWORK • Homework sets will be provided for each chapter’s materials (11...

CHEM 200/202Professor Gregory P. Holland

Office: GMCS-213C

All emails are to be sent to:chem200@mail.sdsu.edu

My office hours will be held in GMCS-212 on Monday from 12 pm to 2:00 pm or by

appointment.

ONLINE TOOLS• Blackboard: one section for each lab.

• Links on sidebar to various resources:

• OWL - online homework and quizzes http://www.cengage.com/owlv2/

• eBook - a pdf version of the book https://openstaxcollege.org/details/chemistry

• New website this semester: sdsuchem200.com

OWL ONLINE HOMEWORK• Homework sets will be provided for each chapter’s

materials (11 chapters in total). HW for CH 3 and 4 due 9/20, next Friday by 11:55 PM

• Four quizzes will be done through OWL, the Thursday prior to each exam. Quiz 1 is 9/19 in OWL, 60 mins timed, 10 questions

• Exam 1 is one week from tomorrow, 9/21 at 2 PM

• Room Assignments for the Exam will be announced next week

SUPPLEMENTAL INSTRUCTION (SI)

• Study sessions lead by former CHEM 200/202 students that excelled in the previous semesters class.

• Occur ~15 times a week.

• Free to access, no reporting to faculty.

• Students who attend SI regularly score on average ~5% higher than those who do not.

LECTURE OBJECTIVES• Chapter 4.1 Writing and Balancing Chemical Equations.

• Write and balance chemical equations in molecular, total ionic and net ionic formats.

• Chapter 4.2 Classifying Chemical Reactions.

• Define 3 types of chemical reactions (precipitation, acid-base, oxidation-reduction).

• Predict solubility of common inorganic compounds by using solubility rules.

• Compute the oxidation states for elements in compounds.

ACID-BASE NEUTRALIZATIONAcid + Base → Water + Salt

Molecular equation

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

Total ionic equation

H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → H2O(l) + Na+(aq) + Cl-(aq)

Net ionic equation

H+(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

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?

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?

GAS FORMATION WITH AN ACID-BASE REACTION

Molecular equation

NaHCO3(aq) + CH3CO2H(aq) → H2O(l) + CH3CO2Na(aq) + CO2(g)

Total ionic equation

Na+(aq) + HCO3-(aq) + H+(aq) + CH3CO2-(aq)→ H2O(l) + Na+(aq) + CH3CO2-(aq) + CO2(g)

Net ionic equationHCO3-(aq) + CH3CO2H(aq) → CH3CO2- + H2O(l) + CO2(g)

• 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

AnswersABCDE

OXIDATION NUMBER RULESGeneral 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 compounds2. For Group 2(A)2 - O.N. is +2 in all compounds3. For hydrogen - O.N. is +1 when bound to nonmetals4. For fluorine - O.N. is -1 when bound to metals & boron5. 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.

Compound O.N. of nitrogenNH3 -3N2H4 -2

NH2OH -1N2 0

N2O +1NO +2NO2- +3NO2 +4NO3- +5

ASSIGNING OXIDATION NUMBERS

(a) H2S(b) SO32-

(c) Na2SO4(d) KNO3(e) AlH3(f) NH4+

(g) H2PO4-

REDOX REACTION IN COMPOUND FORMATION

Electrons 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 REDUCTIONOIL RIG

Oxidationisloss of electrons

Reductionisgain of electrons

LEO GER

Loseelectrons isoxidation

Gainelectrons isreduction

QUESTIONWhat 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 agent AnswerH+ Sn AH+ Sn2+ BSn H+ C

Sn H2 DSn2+ 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 REACTION2HgO(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

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).