examples of chemical % yield (continued) mw 32 44 44 18 given excess 2.2 g mol c 3 h 8 =2.2 =0.050...

Examples of chemical % yield (continued)

MW 32 44 44 18

Given excess 2.2 g Mol C3H8 =2.2 =0.050

44= 4 x 0.05 =0.2 mol 1

Product H2O moles theory

5O2 + C3H8 3CO2 + 4H2O

Bob reports making 4.0 g H2O from 2.2 g C3H8. Is Bob an idiot or okay ?

Bob Reports 4.0 g H2O

Maximum g H2O=18 g/mol*0.2 mol=3.6 g

Bob’s an idiot

Moles level 1Mol-mass-count

Moles level 2•Body parts: mole ratios within a compound•Balancing•% composition/combustion

Moles level 3•Reaction stoichiometry•Limiting and %yields

More practice with ?????

We is done with moles !!!Where we are on the mole road trip….

And now, after many weeks of &^%!! Moles

….for something completely different….CLASSICAL REACTIONs

SLO #6Students will be able to:write, balance, identify and predict common reaction classes (metatheses, acid-base, redox).

Today’s Student Learning Objective (SLO):

Translation:

What happens when I add this to that ?

What to read… chapter 4 ( + a bit of Ch. 14)

Metatheses 153-162

Acid-base 163-170; 653-656

Oxidation-reduction 171-177

CLASSICAL REACTIONs (continued)

Classical Reactions

1) Metathesis (double replacement)

Pb(NO3)2 (aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

Complete Molecular reaction

Pb2+ + 2I- PbI2(s)

Net Ionic Reaction

Pb2+ +2NO3- +2K+ +2I- PbI2(s) + 2K+ +2NO3

-

Complete Ionic Reaction

METATHESIS REACTIONS THIS WEEK IN LAB

1) Metathesis (double replacement) –continued

General characteristics

Ionic, aqueous salts are reactants

Product formed from cation swap is a solid

Low energy…no appreciable heat in/out

Pb2+ + 2I- PbI2(s) Net ionic

CLASSICAL REACTIONs overview (continued)

Let,’s practice a few on the board, kids !

2) Acid-base

HCl(aq) + NaOH(aq) NaCl(aq) + HOH + heat

acid base salt water

Complete Molecular reaction

H+ + OH- H2O

Net ionic reaction

`neutralization

H+ + Cl- + Na+ +OH- Na+ + Cl- +H2O

Complete Ionic reaction

CLASSICAL REACTIONs overview (continued)

Demo reaction: ID the acid, base and salt below

H2SO4 + 2NaOH Na2SO4 + 2H2OAcid Base

Sulfuric acid(car battery acid)

sodium hydroxide(essence of Lye)

sodium sulfate(`Glauber’s Salt =laxative)

salt

2H+ + SO42- +2Na+ + 2OH- 2Na+ + SO4

2- +2H2O

Complete ionic reaction?

Net ionic reaction ?

2H+ + 2OH- 2H2O

Let’s run this one

General characteristicsReactants are specially defined `acid’ and `base’ ionic solutions

Products are soluble salt and water

Significant heat is generated

Indicators signal endpts

H+ + OH- H2O

Net ionic reaction

2) Acid-base…- continued

CLASSICAL REACTIONs overview (continued)

Acid-Base Theories (pp 163-170, 652-655)0) Pre-science: acids and bases are eternal opposites

ACID + BASE = `BALANCE’

Positive + negative = null

Hot + cold = just right

Taoist version

CLASSICAL REACTIONs overview (continued)

Acid-Base Theories (pp 653-656)Modern Theory: Try #1

Svante Arrhenius: Father of the first modern acid/base theory

Young Arrhenius(not considered promising)

Old Arrhenius(wins Nobel prize in 1903 for same acid base theory)

Thesis on Acids & Bases derided by his research committee…

Graduates with Ph.D ordinare(no distinction) see p. 144

CLASSICAL REACTIONs overview (continued)

A measure of this Ph.D `ordinaire’’s brilliance…In 1896 Arrhenius predicted green house gas (CO2) from profligate burning of the the newly popular fuel source …

petroleum oil…would cause (gasp !) measurable and catastrophic global warming…

…starting in 1990-2000 AD

…the entire scientific establishment (and Standard Oil) laughed at him (again)

CLASSICAL REACTIONs OVERVIEW(continued)

FYI….Until 2013 not a single current Republican member of the US Congress admitted that global warming is caused by burning of fossil fuels.

Oil burning starts here

1) Arrhenius Model

HF HCl HBrHNO3 HClO4 H2SO4

H2CO3

H3PO4

BASE

NaOH KOH NH4OH Ca(OH)2 Mg(OH)2

Al(OH)3

Fe(OH)3

ACID =H+ donor

=OH- donor

CLASSICAL REACTIONs overview(continued)

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

ACID + BASE = SALT + WATER

Acid-Base reactions ala’ Arrhenius: A+B= neutral

H2SO4 + Mg(OH)2 MgSO4(aq) + 2H2O

General rule for Arrhenius acid-base

CLASSICAL REACTIONs (continued)

The `Inconvenient Truth’ about the Arrhenius model: basic salts

EXAMPLE: Na2CO3

(sodium carbonate)

No H+ or OH-….=> salt only

CLASSICAL REACTIONs OVERVIEW continued)

The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued)

•Turns pink in presence of phenolphthalein

• gas-forming reaction with HCl, pink disappears

experimental results of adding to water:

EXAMPLE: Na2CO3 (sodium carbonate)

=> A base !!!!????? Where’s OH ???

CLASSICAL REACTIONs OVERVIEW(continued)

The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued)

Other examples of `basic’ salts

Na3PO4 K2SiO3 NaC2H3O2

Basic salts cannot be rationalized using Arrhenius’ acid/base model

CLASSICAL REACTIONs OVERVIEW (continued)

Bronsted to the rescue…

Young Bronsted…Swedish chemist circa 1910…

Young James Dean…American actor circa 1955…(“Rebel Without a Cause,”“East of Eden”, “Giant” )

Winner of the Bronsted look alike contest….

Bronsted a few years after marriage and kids

CLASSICAL REACTIONs (continued)

Bronsted Model of Acids/Bases3 new concepts (see pp 452-453 & 623-6)

Acid=

HF, HCl, HBrHNO3 HClO4 H2SO4 H2CO3

H3PO4

No real change from Arrhenius

proton donor (=H+)

CLASSICAL REACTIONs OVERVIEW(continued)

ARRHENIUS ACIDS = BRONSTED ACIDS

New Concept #1: Follow the protons

BASE=

OH-

CO3-2 ,PO4

-3, C2H3O2-,SiO3

-2…

proton acceptor

CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES: New Concept #1: following the protons (cont.)

The set of Bronsted bases includes Arrhenius bases + ….

…nearly any negative ion (=anion) that even weakly attracts protons

Examples of Bronsted Bases

How the proton acceptor creates the basic salt effect:

CO32- + H-OH

..Bronsted Base is basic in water because it splits water to make OH- !

Hydrolysis reaction

CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:

New Concept #2

Hydrolysis…Bronsted bases `split’ water !!!

EXAMPLE

HCO3- + OH-

Conjugate idea is like going drag…Men=acid Women=base

BASE ACIDCONJUGATE ACID

CONJUGATEBASE

Identify `acids’ and bases

BRONSTED’S MODEL OF ACIDS/BASES: New Concept #3a: conjugate

acid/base pairs

CO32- + H-OH

Acid conjugate baseBase conjugate acid

Base Acid

Conjugate acid

Conjugate base

CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:

New Concept #3a: conjugate acid/base pairs

HCO3- + OH-

Identify `acid’ and baseIdentify conjugate acid and base

PO43- + HCO3 - HPO4

2- + CO32-

Acid conjugate baseBase conjugate acid

acidbaseconjugate base

conjugateacid

new concept #3a: Conjugates (continued)

When acid and base reacts….

EXAMPLE: IDENTIFY ACID, BASE AND THEIR CONJUGATE BASE AND ACID ABOVE

ACID + BASE CONJUGATE BASE + CONJUGATE ACID

Bronsted Model

Contrast to Arrhenius Model

ACID + BASE SALT + WATER

CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:

New Concept #3b:

spontaneous acid + base reactions produce weaker acids + bases

Both products `neutral’

ARRHENIUS

ACID-BASE THEORIES SUMMARIZED

BRONSTED

ACID = H+ DONOR PROTON DONOR

BASE= OH- DONOR PROTON DONOR

ACID + BASE

SALT + WATER

CONJUGATE ACID + CONJUGATE BASE

What observation required Bronsted to create a new Acid/Base Theory different than Arrhenius’s model ?

A. Many salts formed conjugate acids.

B. Spontaneous acid+base reactions only occurred if weaker acids and bases formed.

C. H2O spontaneously decomposed to OH- and H+ in presence of various salts.

D. Many salts without OH- somehow created OH- in water.

Many sa

lts fo

rmed co

nju...

Spontaneous a

cid+base

r...

H2O spontaneously

dec...

Many sa

lts w

ithout O

H-...

25% 25%25%25%

Which part of the Bronsted salt K3PO4 is the proton acceptor ?

A. K+

B. O2-

C. P3-

D. PO43-

E. K3PO4

F. OH-

K+O2-

P3-

PO43-

K3PO4OH-

17% 17% 17%17%17%17%

What new concept of Bronsted’s most directly explains why many salts are bases?

A. The anionic part of salts can hydrolyze water.

B. Spontaneous acid/base reactions lead to weaker conjugate acids/bases.

C. Bronsted bases are proton acceptors.

D. Bronsted acids are proton donors.

The anionic part

of salts

...

Spontaneous a

cid/b

ase r.

..

Bronste

d bases a

re pro

to...

Bronste

d acids a

re pro

to...

25% 25%25%25%

In-class reaction Jeopardy

Low heat, precipitates, cation swap metathesis

WHAT IS…

Na2CO3 for example A Bronsted baseWhat’s my reaction type:

HCl + KOH KCl + H2O

Acid/base neutralization (Arrhenius)

Pick the Arrhenius acids

H2O HNO3 NaHCO3 HBr NaCl HNO3 HBr

In-class reaction JeopardyWHAT IS…

What’s my reaction type:K3PO4 + H2O HK2PO4 + KOH

Acid/base hydrolysis(Bronsted)

Write my products ?

AgNO3(aq) + NaCl(aq) ?AgCl(s) + NaNO3(aq)

Pick the Bronsted base(s)

NaOH HBr NaHCO3 K3PO4

NaOH NaHCO3 K3PO4

Pick the Arrhenius basesNaOH