brian corry summer 2012/13

Choosing Contexts and Experiments that Help Students Make Connections in Chemistry

RET Program Summary

Brian CorrySummer 2012/13

Designing Curriculum Units that Help Students Make Connections in Chemistry

RET Program Summary

Brian CorrySummer 2012/13

My background• Arrowhead High School

– Hartland, WI– AP Chemistry– General Physics and AP Physics

• Procter & Gamble– Cincinnati, OH– Researcher, Drying and Particle

Formation

• University of Illinois– Champaign, IL– BS Chemistry

Presentation Outline• Summary of RET Experiences and

Research• Connecting the research to chemistry

education / instructional model• Design criteria for curriculum that

helps students make connections• Curriculum Unit Example

RET Program• Research Experience for

Teachers– University of Wisconsin –

Milwaukee– Supported by NSF– Objective: collaborate with

MS / HS science teachers to improve the quality of science education

My Faculty Mentor• Dr. Alan Schwabacher

– UWM– PhD, Columbia– Organic Chemistry– Research focuses on

mimicking the selective binding of biological molecules

Catalyzed Hydrolysis of

BNPPChem 582 at UWM

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

bis(p-nitrophenyl) phosphate (BNPP) p-nitrophenol

Slow

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

p-nitrophenol

Cu2+, Fast

bis(p-nitrophenyl) phosphate (BNPP)

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

p-nitrophenol

Cu2+, Fast

bis(p-nitrophenyl) phosphate (BNPP)

Michaelis-Menten Kinetics

Hydrolysis of BNPP

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

Hydrolysis of a phosphate diester

Phosphate diesters are extremely important biologically

Hydrolysis of BNPP

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

Biochemistry

Hydrolysis of a phosphate diester

Kinetics / Catalysis

RateCatalyst?

O-

NO2

pKa = 7.16

Acid / Base

Yellow

pKa = 2.79pKa1 = 0.30 pKa2 = 4.96

O2N

O

P

OH

O-

O

O-

NO2

+

O2N

O

P

O

O-

O

NO2

+ OH2

Hydrolysis of BNPP

O2N

O

P

O

OHO

NO2

+ OH2

OH

NO2O2N

O

P

OH

OHO

+

Biochemistry

Hydrolysis of a phosphate diester

Kinetics / Catalysis

RateCatalyst?

O-

NO2

pKa = 7.16

Acid / Base

Yellow

Analytical / Spectroscopy

pKa = 2.79pKa1 = 0.30 pKa2 = 4.96

Hydrolysis of BNPP

Biochemistry

Kinetics / Catalysis Acid / Base

Analytical / Spectroscopy

10 g BNPP = $31510 g NaBNPP = $1500

Synthesis of BNPP

Synthesis of TNPP

250 g = $36 50 g = $27

O2N O

P

O

O

O

O2N

NO2

Et3N, CH 2Cl2+ 3 Et3NH+Cl-

1st time: 53% yield2nd time: 70% yield

PCl

O

Cl

Cl + 3

OH

NO2

TNPP

O2N O

P

O

O

O

O2N

NO2

+ OH2M EK, reflux

O2N

O

P

O

OHO

NO2

+

OH

NO2BNPP

1st time: 46% yield2nd time: 52% yield $400

Hydrolysis of BNPP

Biochemistry

Kinetics / Catalysis Acid / Base

Analytical / Spectroscopy

Hydrolysis of BNPP

Biochemistry

Kinetics / Catalysis Acid / Base

Analytical / Spectroscopy

Synthesis of TNPP/BNPP

Organic Synthesis

NMR / Characterization

Extraction / Purification TLC / Polarity

Absorbance is directly proportional to [PNP] =

Beer’s Law

O-

NO2

We can monitor the progress of reactions.

OH-

O2N

O

P

O

O-

O

NO2

O2N

O

P

OH

O-

O

+

O-

NO2

Rate is not first order…

…if you ignore ionic strength.

OH-

O2N

O

P

O

O-

O

NO2

O2N

O

P

OH

O-

O

+

O-

NO2

Rate is first order with respect to hydroxide.

OH-

O2N

O

P

O

O-

O

NO2

O2N

O

P

OH

O-

O

+

O-

NO2

Rate is first order with respect to BNPP.

OH-

O2N

O

P

O

O-

O

NO2

O2N

O

P

OH

O-

O

+

O-

NO2

A catalyst increases the rate of reaction.

Outcomes• Chemistry 582

– More effective synthetic route for BNPP– Students make their own reagents– Michaelis-Menten kinetics (not yet?)

• AP Chemistry– Access to expensive materials– Phosphate esters– PNP in Beer’s Law activity– BNPP to study kinetics/catalysis

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Collaboration Infrequent. Perhaps different groups pooling data.

Constant. Shared ownership of separate pieces.

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Collaboration Infrequent. Perhaps different groups pooling data.

Constant. Shared ownership of separate pieces.

Peer learning / communication

Rare. Some models of project-based learning.

Researchers and students teach one another.

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Collaboration Infrequent. Perhaps different groups pooling data.

Constant. Shared ownership of separate pieces.

Peer learning / communication

Rare. Some models of project-based learning.

Researchers and students teach one another.

Role of content Content is the focus. Laboratory experiences are a vehicle for investigating the content.

Chemistry content is obtained and used in the service of answering a research question.

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Collaboration Infrequent. Perhaps different groups pooling data.

Constant. Shared ownership of separate pieces.

Peer learning / communication

Rare. Some models of project-based learning.

Researchers and students teach one another.

Role of content Content is the focus. Laboratory experiences are a vehicle for investigating the content.

Chemistry content is obtained and used in the service of answering a research question.

Assessment of outcomes

Separates content and lab practices objectives. Original research findings seldom critiqued.

Integrates laboratory and content. Research findings necessarily critiqued.

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Primary owner Instructor Researcher or student

Collaboration Infrequent. Perhaps different groups pooling data.

Constant. Shared ownership of separate pieces.

Peer learning / communication

Rare. Some models of project-based learning.

Researchers and students teach one another.

Role of content Content is the focus. Laboratory experiences are a vehicle for investigating the content.

Chemistry content is obtained and used in the service of answering a research question.

Assessment of outcomes

Separates content and lab practices objectives. Original research findings seldom critiqued.

Integrates laboratory and content. Research findings necessarily critiqued.

Topics / disciplines One at a time. Some topics will be merged in advanced classes.

Multidisciplinary. Boundaries between topics blurred.

“When a school subject is taught for which there is a

professional counterpart, there should be a conceptual

connection to post-secondary studies and to the practice of that subject in the real world.”

National Research Council. (2009). Engineering in K-12 education: Understanding the status and improving the prospects. Washington, DC: The National Academies Press.

Standard Chemistry Education

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Structure

Content / Context

ChemistryExpected Outcome

Standard Chemistry Education

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Structure

Actual Outcome Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

“Your system is perfectly designed

to give you the results you're

getting.”W. Edwards Deming

Which outcome do we want?

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Content / Context

Chemistry

Outcome 1

Outcome 2

Unit Expectations

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Structure

Content / Context

ChemistryExpected Outcome

Course Expectations

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Structure

Content / Context

ChemistryExpected Outcome

Alternative Model

Content

Unit 1

Context

Content

Unit 2

Content

Unit 3

Content

Unit 4

Structure

Content / Context

ChemistryExpected Outcome

Alternative Model

Content

Unit 1

Context

Content

Unit 2

Content

Unit 3

Content

Unit 4

Structure

Content / Context

ChemistryExpected Outcome

Alternative Model

Content

Unit 1

Context

Content

Unit 2

Content

Unit 3

Content

Unit 4

Structure

Content / Context

ChemistryExpected Outcome

Important Design Consideration

Content

Unit 1

Content

Unit 2

Content

Unit 3

Content

Unit 4

Structure

ChemistryExpected Outcome

Context

Content / Context

Important Instructional Consideration

Context

Content

Unit 2

Content

Unit 3

Content

Unit 4

Structure

Content / Context

ChemistryExpected Outcome

Content

Unit 1

http://chemistry.beloit.edu/modules.html

These 2-4-week modules start with relevant real-world questions and develop the chemistry needed to answer them. In the process, students model how chemistry is actually done and discover connections between chemistry and other sciences, technology, and society.

Other curriculum materials

ACS CLUE Living by Chemistry

3 Important Design Criteria

Context

Connections

Questions

AP Chemistry “Big Ideas”

Big Ideas

Atomic Structure

Structure and

Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

AP Chemistry “Big Ideas”

Big Ideas

Atomic Structure

Structure and

Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

UnitsAtomic

Structure

Structure and Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

1

2

3

4

5

6

Context

Atomic Structure

Structure and Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

ACS Anchoring Concept Content Map (ACCM)

Context

Atoms

Bonding

Structure & Function

Inter-molecular

forces

ReactionsEnergy / Thermo-dynamics

Kinetics

Equilibrium

Experiments, Measurement

& Data

Visualizations

Context Example: NH3

• Bonding and structure• IMFs and Properties• Reactions and Stoichiometry

– Haber Process– Acid-base / Complex Ions

• Kinetics• Equilibrium• One problem: Data and experimentation

(Haber)

NH3 Production

Atomic Structure

Structure and Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

Context

Atomic Structure

Structure and Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

3 Important Design Criteria

•Rich enough to touch all “big ideas”•Explicitly developed to address them all•Appropriate level / familiarity

Context•Modeling the use of the big ideas to make

connections•Students are challenged to make these

connections

Connections

•Effective vehicle for making connections•Requires/promotes student engagement•Teachers need well-planned progressions

Questions

Classroom vs. Research LabFeature High School Chemistry Graduate Chemistry Research

Focus of work Units of content Research question

Science, 1987, 235, 1173-1178

Organic Phosphates

Atomic Structure

Structure and Properties

Reactions

Kinetics

Thermo-dynamics

Equilibrium

Traditional: How is DNA built?

DNA

Bases Ribose Phosphate

Introductory Activity

DNA is made up of…

Traditional: How is DNA built?

DNA

Bases

Structure

Function

Ribose

Structure

Function

Phosphate

Structure

Function

Introductory Activity

Alternative: What does DNA have to do?(and what about its structure allows it to do this?)

DNA

Functions

Information

Bases

Structure

Framework

Ribose

Structure

Glue

Phosphate

Structure

Introductory Activity

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

Why not A/G and T/C?

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

N

N

N

N

NH H

Ribose

A den ine

N

N

N O

H

H

Ribose

C ytos ine

N

N

N

N

N

O

Ribose

H

H

H

G uan ine

N

N

O

O

CH3

Ribose

H

Thym ine

PurinesPyrimidines

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

How do they hold together?

Why not A/G and T/C? Structural models / “rung” building Uneven spacing of ladder rails

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

Structural models

C ytos ineG uan ine

N

N

ON

NRibose

N

H

H

H

N

N

RiboseO

N

H

H

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

How do they hold together? Structural models Hydrogen bonds

Why not A/G and T/C? Structural models / “rung” building Uneven spacing of ladder rails

Why not A/C and T/G?

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

DNA Base Pairing Applet

http://chemmac1.usc.edu/java/bases/basepairs.html

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

What do base pairs do (dynamically) in DNA? Replication process

How do they hold together? Structural models Hydrogen bonds

Why not A/G and T/C? Structural models / “rung” building Uneven spacing of ladder rails

Why not A/C and T/G? Structural models / pairing applet No H-bond match up

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

What do base pairs do (dynamically) in DNA? Replication process Hold together and break apart

How do they hold together? Structural models Hydrogen bonds

How do they break apart?

Replication animations

Why not A/G and T/C? Structural models / “rung” building Uneven spacing of ladder rails

Why not A/C and T/G? Structural models / pairing applet No H-bond match up

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/

Driving QuestionWhy did nature choose those bases and pair them that way?

What do base pairs do (statically) in DNA?

Questions Investigations

Structure of DNA polymers

Explanations

“Rungs” of the ladder

What do base pairs do (dynamically) in DNA? Replication process Hold together and break apart

How do they hold together? Structural models Hydrogen bonds

How do they break apart?

Replication animations DNA helicases

Why not A/G and T/C? Structural models / “rung” building Uneven spacing of ladder rails

Why not A/C and T/G? Structural models / pairing applet No H-bond match up

What must each “rung” do? Ladder

1) Code information2) Space the rails evenly3) Hold the rails together

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate?

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate? Drawing LDS Common oxyanion with resonance forms, conjugate base of H3PO4

What is phosphoric acid? Working with LDS

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate? Drawing LDS Common oxyanion with resonance forms

What is phosphoric acid? Working with LDS Phosphate group with a hydrogen

attached to three oxygens

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

How acidic is phosphoric acid? Titration curve

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate? Drawing LDS Common oxyanion with resonance forms

What is phosphoric acid? Working with LDS Phosphate group with a hydrogen

attached to three oxygens

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

How acidic is phosphoric acid? Titration curve pKa values for three acidic

hydrogens

How does pH affect ionization?

Henerson-HasselbalchChemistry Version (what’s the pH?)

acidbaselogppH aK

Biochemistry Version (what’s there at that pH?)

aKppH10acidbase

H2PO4- HPO4

2-H3PO4

PO43-

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate? Drawing LDS Common oxyanion with resonance forms

What is phosphoric acid? Working with LDS Phosphate group with a hydrogen

attached to three oxygens

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

How acidic is phosphoric acid? Titration curve pKa values for three acidic

hydrogens

How does pH affect ionization?

HH Calculations / Speciation Curve

pH determines extent of ionizationAt pH=7, 50/50 H2PO4

-/HPO42-

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester?

OHP

O

OHOH

OP

O

OHOH

R

Phosphoric Acid Phosphate Ester

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

How many hydrogens are replaced?

OHP

O

OHOH

OP

O

OHOH

CH3

OP

O

OHO

CH3

CH3

OP

O

OO

CH3

CH3

CH3

Phosphoric Acid Phosphate monoester

Phosphate triesterPhosphate diester(like DNA)

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

What does replacing hydrogen do to acidity?

Mono/di/tri ester consideration

How many hydrogens are replaced? Research It depends. There are phosphate

mono-, di-, and tri- esters.

OHP

O

OHOH

OP

O

OHOH

CH3

OP

O

OHO

CH3

CH3

OP

O

OO

CH3

CH3

CH3

Phosphoric Acid Phosphate monoester

Phosphate diester(like DNA)

Phosphate triester

1

23 1

1

2

No acidic hydrogens

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

What does replacing hydrogen do to acidity?

Mono/di/tri ester consideration

Triesters have 0 acidic hydrogens. Diesters have 1, monoesters 2.

What are the relative pKas for each of these?

How many hydrogens are replaced? Research It depends. There are phosphate

mono-, di-, and tri- esters.

Handbook of Biochemistry and Molecular Biology

OHP

O

OHOH

OP

O

OHOH

CH3

OP

O

OHO

CH3

CH3

OP

O

OO

CH3

CH3

CH3

Phosphoric Acid Phosphate monoester

Phosphate triester

1

23 1

1

2pKa1 = 2.1

pKa2 = 7.2 pKa3 = 12.3 pKa1 = 1.5

pKa2 = 6.3

pKa = 1.3 No acidic hydrogens

Phosphate diester(like DNA)

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

What does replacing hydrogen do to acidity?

Mono/di/tri ester consideration

Triesters have 0 acidic hydrogens. Diesters have 1, monoesters 2.

What are the relative pKas for each of these? Research pKa1 ≈ 1-2 for all

How many hydrogens are replaced? Research It depends. There are phosphate

mono-, di-, and tri- esters.

What are the major species at pH = 7?

OHP

O

OHOH

OP

O

OHOH

CH3

OP

O

OHO

CH3

CH3

OP

O

OO

CH3

CH3

CH3

Phosphoric Acid Phosphate monoester

Phosphate triester

1

23 1

1

2pKa1 = 2.1

pKa2 = 7.2 pKa3 = 12.3 pKa1 = 1.5

pKa2 = 6.3

pKa = 1.3 No acidic hydrogens

Phosphate diester(like DNA)

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

What does replacing hydrogen do to acidity?

Mono/di/tri ester consideration

Triesters have 0 acidic hydrogens. Diesters have 1, monoesters 2.

What are the relative pKas for each of these? Research pKa1 ≈ 1-2 for all

How many hydrogens are replaced? Research It depends. There are phosphate

mono-, di-, and tri- esters.

What are the major species at pH = 7?

pKa, Calculations, graphs

Phosphate diesters are ionized at pH 7.

Where is the “A” in DNA?

Driving QuestionWhy did nature choose phosphates?

How is DNA like phosphoric acid?

Questions Investigations

Structure of DNA polymers

Explanations

Two hydrogens replaced by a carbon of the ribose

What is a phosphate ester? Research Phosphoric acid with carbon groups

replacing the hydrogens

What does replacing hydrogen do to acidity?

Mono/di/tri ester consideration

Triesters have 0 acidic hydrogens. Diesters have 1, monoesters 2.

What are the relative pKas for each of these? Research pKa1 ≈ 1-2 for all

How many hydrogens are replaced? Research It depends. There are phosphate

mono-, di-, and tri- esters.

What are the major species at pH = 7?

pKa, Calculations, graphs

Phosphate diesters are ionized at pH 7.

Where is the “A” in DNA? Discussion DNA is not an “acid” at pH 7

Driving QuestionWhy did nature choose phosphates?

What does that piece of the chain have to

do?

Questions Investigations

Structure of DNA polymers

Explanations

Link things in the DNA chain.

What type of bonding behavior is required? Discussion The unit in that space has to be

able to link at least two times

What elements / groups could do this? Brainstorming Yes: O, S, N, P, As, molecule

No: H, Halogens

What is a phosphate? Drawing LDS Common oxyanion with resonance forms

What is phosphoric acid? Working with LDS Phosphate group with a hydrogen

attached to three oxygens

Nature uses phosphates. Let’s learn about those and assess some of the alternatives later.

How acidic is phosphoric acid? Titration curve pKa values for three acidic

hydrogens

How does pH affect ionization?

HH Calculations / Speciation Curve

pH determines extent of ionizationAt pH=7, 50/50 H2PO4

-/HPO42-

O

P OO-

O

R2

R1

O

R1

R2 O

CO

O

R2

R1

O

S OO

O

R2

R1

O

As OO-

O

R2

R1

OO

O OO

-O

OH

R2R1

Phosphate esterEther

Ester Sulfate Ester

Citrate(?) EsterArsenate Ester

Driving QuestionWhy did nature choose phosphates?

What’s the importance of being ionized?

Questions

Solubility

Kinetics

Energetics

3 Important Design Criteria

•Rich enough to touch all “big ideas”•Explicitly developed to address them all•Appropriate level / familiarity

Context•Modeling the use of the big ideas to make

connections•Students are challenged to make these

connections

Connections

•Effective vehicle for making connections•Requires/promotes student engagement•Teachers need well-planned progressions

Questions

The role of experiments

Content

Unit 1

Context

Content

Unit 2

Context

Content

Unit 3

Context

Content

Unit 4

Context

Design 1

Design 2Questions Investigations Explanations

How acidic is phosphoric acid? Titration curve pKa values for three acidic

hydrogens

Questions?corry@arrowheadschools.org