pH and Titrations

Lesson Created by: Lauryn Atwood

Length of lesson: 1 week

Description of the class: Heterogeneous

Name of course: Chemistry

Grade level: 10-12

Honors or regular: Regular

Source of the lesson:

http://www.ausetute.com.au/titrcurv.html

http://www.cstephenmurray.com/Acrobatfiles/IPC/chapter22to25/chap25no1.pdf

http://www.sciencecompany.com/images/phscale.gif

http://teachers.ausd.net/classlink/getfile.ausd?fileid=45821

TEKS addressed:

(2) Scientific processes. The student uses scientific methods to solve investigative questions. The student is expected to:

(E) Plan and implement investigative procedures, including asking questions, formulating testable hypotheses,

and selecting equipment and technology, including graphing calculators, computers and probes,

sufficient scientific glassware such as beakers, Erlenmeyer flasks, pipettes, safety goggles, and burettes,

and an adequate supply of consumable chemicals;

(F) Collect data and make measurements with accuracy and precision;

(G) Express and manipulate chemical quantities using scientific conventions and mathematical procedures,

including dimensional analysis, scientific notation, and significant figures.

(I) communicate valid conclusions supported by the data through methods such as lab reports, labeled

drawings, graphs, journals, summaries, oral reports, and technology-based reports.

(10) Science concepts. The student understands and can apply the factors that influence the behavior of solutions. The

student is expected to:

(I) define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution

I. Overview

The purpose of this lesson is to familiarize students with the concept of pH. Students will conduct neutralization

reactions and understand how the pH changes. Students will construct titration curves and determine endpoints

of titration from these curves, then use this endpoint to help in the calculations of molarity of an unknown base.

The students will also conduct an investigation of pH of household products.

II. Performance or learner outcomes

Students will be able to:

Write balanced neutralization reaction equations

Find the endpoint of titration

Construct a titration curve

Titrate an unknown concentration of base with an acid

Calculate the molarity of an unknown base

Investigate the pH of household products

III. Resources, materials and supplies needed Engage:

5 test tubes per group

1 beaker per group

5 test tubes for the teacher

1 beaker for the teacher

1 pipette per group

Universal Indicator

Litmus paper (5 pieces per group)

Phenolphthalein

Chemicals: 0.1 M HCl, 0.1 M NaOH, 0.1M CH3COOH, 0.1 M NH3, water

Goggles per student

Explore:

1 burette per group

1 graduated cylinder per group

2 beakers per group

Goggles per student

1 funnel per group

pH meter per group

Chemicals: 0.1 M HCl, ~0.1 M NaOH

Computer per group (with Excel)

Elaborate:

Universal Indicator

Buffers (pH 1-14)

8 test tubes per group

pH meter per group

Milk

Lemon juice

Aspirin

Shampoo

Bleach

Windex

Coca-cola

Dishwashing soap

IV. Supplementary materials, handouts. (Also address any safety issues

Concerning equipment used)

pH exit slip, titrations quiz, indicators quiz, Titrations lab, pH of household products lab, Acids/Bases PowerPoint,

MSDS Sheets

V. Safety Issues

Chemicals are used in this lesson. Students should wear goggles, long pants (past the knee), and close-toed shoes at any

time they have chemicals. Students may opt to wear aprons as well to protect their clothes. MSDS Sheets for each of the

four chemicals (HCl, NaOH, CH3COOH, and NH3) are provided at the end of the lesson.

If any glass breaks, students should notify the teacher immediately and keep people clear from the area. The teacher

should then dispose of the broken glass properly (not in a trash can).

VI. Accommodations for learners with special needs (ELLs, Special Ed, 504, G&T)

ELL, Special Ed, 504: Guided notes

G&T: lesson extentions (polyprotic acids)

Five-E Organization

Teacher Does Probing Questions Student Does

Engage: Learning Experience(s)

[Indicator Activity]

Advanced preparation: Fill

five labeled (A-E) test tubes ¼

full with chemicals of

different pH levels before

class. (1-HCl, 2-CH3COOH,

3-H2O, 4-NH3, 5-NaOH)

Also, prepare the Universal

Indicator, by putting ~5 drops

in each table’s beaker, then

fill the beaker with water.

Each group has 5 test tubes

with different liquids in each.

Put 3 drops of the liquid from

your beaker into test tube A.

Add 3 drops of the liquid from

the beaker into test tube A to

each of the other 4 test tubes.

In your beaker, there is water

with something we call a pH

indicator. It tells us about an

important property of

compounds, called pH.

Critical questions that will

establish prior knowledge and

create a need to know

What observations can you

make about these 5 liquids?

What observations can you

make about your beaker?

What do you think will happen

when you add 3 drops of the

liquid from the beaker into test

tube A?

What happened?

Why?

What will happen when you

add 3 drops of the liquid from

the beaker into test tubes B-E?

What happened?

Why?

Expected Student

Responses/Misconceptions

They are clear; they might be

different.

It is also clear.

It might change colors;

nothing.

The solution turned red!

A chemical reaction

They will also turn red; they

may turn different colors.

They turned different colors!

There were different chemicals

in each of the beakers that

reacted differently with the

liquid from the beaker

The pH of a compound is a

measure of acids and bases

and goes by a scale from 0-14.

The more acidic a compound

is, the lower the pH. The more

basic a compound is, the

higher the pH. Neutral

compounds, like water, have a

pH of 7.

Show the Universal

Indicator scale. This scale

shows the different colors that

the solution will turn when it

hits a certain pH. We can

essentially figure out the

concentration of H+ ions in a

solution by knowing its pH.

Use phenolphthalein as a

demonstration and then have

students use litmus paper to

demonstrate uses of other

indicators.

Approx. Time 20 mins

What is a Universal Indicator?

How is it different from a

specific color indicator?

What is pH?

Shows pH at a variety of levels

A specific color indicator only

changes color once, while a

universal indicator can change

to a bunch of different colors,

depending on the pH.

A measure of acids and bases.

It measures the hydrogen ion

concentration.

Evaluation(Decision Point

Assessment):

Indicators quiz.

pH exit slip.

The assessment you will use to

determine what to do next.

What student outcome will

indicate that you should move

on to the exploration? What

will you do if the outcome is

something else?

Explore:

Learning Experience(s)

Today, we’ll be talking about

neutralization reactions. We

discussed neutralization

Critical questions that will

allow you to decide whether

students understand or are

able to carry out the assigned

task (formative)

Expected Student

Responses/Misconceptions

reactions last week and a

group gave a presentation on

them.

You are going to conduct two

neutralization reactions, or

titrations, using a strong acid

and a strong base. One

titration will be done with a

color indicator. The other will

be done with a pH probe.

Write down a hypothesis in

the correct space on your lab

sheets.

Separate students into

groups of four. Pass out job

cards.

You will have a specific job

for this experiment.

Titrator: Adds a few drops of

the titrant (base).

Burette reader: Reads the

burette after every few drops

of titrant are added.

pH Probe Reader: Reads the

pH meter to get a value for

each burette reading.

Recorder: Records the pH and

What is a neutralization

reaction?

Where would a strong acid be

on the pH scale? A strong

base?

If we are mixing these two

substances, which are on

opposite ends of the pH

spectrum, together, what might

we want to know?

What do you think will happen

to the pH when you mix these

substances together?

Why?

What are we forming in a

neutralization reaction?

What is the pH of water?

What does this mean for the

pH of the substances you mix

together?

When an acid and a base

combine to form a salt and

water.

0; 14

What the ending pH will be.

Misconceptions: Nothing; they

will change colors; they will

become more acidic/basic.

Various responses.

A salt and water.

7 (neutral)

They should be about 7.

burette reading on a blank

sheet of paper after each few

drops.

[Teacher Note: If students

don’t have access to a pH

probe, a universal indicator

can be used, marking the

volumes of base used for each

color change.]

If you are the recorder, rinse

the burette. pH probe readers,

set up the pH probe in the

beaker. Burette readers, fill

the burette after it is rinsed

and tell the recorder the initial

reading on the burette.

Titrators, prepare the analyte.

Pass out lab skills checklist.

Conduct titrations and assess

lab skills.

After you finish conducting

the titration, clean up

properly.

[Constructing a Titration

Curve]

Construct a titration curve by

following the instructions

given.

Find and record the endpoint

of titration for your

experiment.

What do you notice about this

curve?

What do you think is

happening when the pH is

steady at the beginning?

What is happening during the

steep, quick rise?

What is happening when the

pH becomes steady again

towards the end of your

titration?

How can we determine the

endpoint of titration?

It gets really straight and

perpendicular in the middle

and levels off horizontally on

both ends.

Moles acid >> moles base

Moles acid ~ moles base

Moles base >> moles acid

Find the middle of the steep

part of the curve.

Approx. Time 70 mins

Evaluation(Decision Point

Assessment):

Titration Lab Skills Checklist

during the lab.

Alternative Assessment: Skill

Tasks – Titration lab

Titrations quiz

The assessment you will use to

determine what to do next.

What student outcome will

indicate that you should move

on to the explanation? What

will you do if the outcome is

something else?

Students should all average

proficient lab skills. If not, go

over important lab skills

needed for this lab.

Students will use cooperative

roles to conduct titrations.

Explain:

Learning Experience(s)

[Acids/Bases PowerPoint]

[Stoichiometry Review]

Review stoichiometry and

dimentional analysis.

[Calculating the Molarity of

an Unknown Base]

If we know the concentration

of the acid, we will be able to

calculate the concentration of

the base!

Write the balanced chemical

equation on the board.

The coefficient for each

compound (the number in

front) represents the number

of moles of that compound.

Critical questions that will

allow you to help students

clarify their understanding

and introduce information

related to concepts to be

learned

Why is stoichiometry useful?

How can stoichiometry be

used in this experiment?

What is the balanced chemical

equation for the titration we

did?

There are no numbers in front

of any of these compounds,

what does this mean?

So does this mean there was

constantly 1 mole of HCl when

we titrated?

Expected Student

Responses/Misconceptions

It allows us to do conversions

To find the concentration of

the base.

HCl + NaOH NaCl + H2O

That it represents only one

mole for each compound.

No.

These numbers are ratios.

This means that at equilibrium

for every one mole of HCl, we

have one mole of NaOH, one

mole of NaCl, and one mole

of water.

This gives us (0.025X) moles.

Now we know the number of

moles of base, but we’re

trying to find the

concentration of the base.

Looking at your titration

curves, find the endpoint of

titration.

Looking at this stoichiometry,

let’s take our balanced

equation and look at both

sides to find the concentration

a different way. [Use the

empirical formula, M1V1 =

What is the known

concentration of acid? (Given)

If we have X M of acid, what

does the M stand for?

How can we figure out how

many moles of acid we started

out with?

What do we know about the

ratio of moles in this titration?

What does this mean about

moles at the endpoint of

titration?

How many moles of base got

us to the endpoint of titration?

What are the units for

concentration, again?

What else do we know about

the base in this experiment?

At which point in our titration

curve are we looking?

Why?

How much base did you add to

get to the endpoint of

titration?

How can we use this

information to find the

concentration of the base?

[value - X]

Molarity; moles per liter

Multiply by the amount (in

liters) of acid used.

There is a 1:1 ratio.

There will be an equal number

of moles of acid and base.

(0.025X) moles

Molarity; moles per liter

How much we added.

The endpoint

Because that is when the pH is

7 and the moles acid = moles

base for this experiment.

Y mL

Convert mL to L, then divide

the number of moles by this

number.

M2V2 to find the

concentration again]

Approx. Time 45 mins

Evaluation(Decision Point

Assessment)

Titrations quiz

The assessment you will use to

determine what to do next.

What student outcome will

indicate that you should move

on to the extension? What will

you do if the outcome is

something else?

Extend / Elaborate:

Learning Experience(s)

[pH Testing of Household

Products]

We are going to investigate

pH of household products.

First, hypothesize whether

each of the items we are

testing are acids or bases.

Justify your hypotheses.

Conduct investigation. (from

http://teachers.ausd.net/classli

nk/getfile.ausd?fileid=45821)

Approx. Time 45 mins

Critical questions that will

allow you to decide whether

students can extend conceptual

connections in new situations

Expected Student

Responses/Misconceptions

Evaluation(Decision Point

Assessment):

Alternative assessment -

Investigation

The assessment you will use to

determine what to do next.

What student outcome will

indicate that you should move

on to the final evaluation?

What will you do if the

outcome is something else?

Evaluate:

Lesson Objective(s)

Learned (WRAP –UP at end)

-> Summarize

Submit a 1 page paper taking

the stance of either a company

that manufactures pH meters,

a company that produces a

specific indicator (like

phenolphthalein), or a

company that produces a

universal indicator. Give an

Critical questions that will

allow you to decide whether

students understood main

lesson objectives

Expected Student

Responses/Misconceptions

explanation as to why the

consumer would be better off

using your product for their

experiments than another.

Prepare a poster to sell your

product to the class.

Project question:

How do pH and titrations

relate to my topic of interest?

Approx. Time 40 mins

Acids/Bases PowerPoint Presentation – Page 1

Acids/Bases PowerPoint Presentation – Page 2

Titrations Materials:

2 beakers

1 burette

1 funnel

1M HCl

Unknown concentration of NaOH

Stir/hot plate

Magnetic stir bar

Job Roles: (CIRCLE YOUR JOB ROLE)

Titrator: Adds a few drops of the titrant (base).

Burette reader: Reads the burette after every few

drops of titrant are added.

pH Probe Reader: Reads the pH meter to get a

value for each burette reading.

Recorder: Records the pH and burette reading on a

blank sheet of paper after each few drops.

Your task: To determine the unknown concentration of NaOH

Preparation Procedure: Rinse a burette with your base – Recorder

Put a waste beaker underneath the burette. Using your funnel, put a small amount of base in the burette and let it

run through, with the stopcock open.

Preparing the titrant – Burette Reader

The titrant is the substance you will use to titrate (in this case, it is the base). Carefully fill the burette to the 5mL

mark (at the top of the burette) with sodium hydroxide (NaOH), using your funnel. Record this as your initial

reading.

Preparing the analyte – Titrator

The analyte is the substance you will be titrating (in this case, it is the acid). Collect 25mL of 0.1M hydrochloric

acid (HCl) in a graduated cylinder. Record the exact amount of HCl you have collected. Transfer the HCl into a

clean, dry beaker.

Preparing the setup – pH Probe Reader

Put the beaker with the analyte underneath the burette that is filled with the titrant. Secure the pH probe on the

side of the beaker. Be sure that the glass bulb is submerged in the liquid, but does not touch the bottom of the

beaker. Put a magnetic stir bar in the beaker and turn the stirrer on (not the heat!).

Titration Procedure: Titrate the analyte with the titrant with a few drops, then stop record the burette reading and pH. Your solution’s

pH will not change much in the beginning. It is okay to titrate 2-3mL when it doesn’t change much. When the numbers do

start changing rapidly, only titrate 1-3 drops at a time. Do this until the pH of your solution becomes steady again.

Data:

Volume of HCl

Initial Burette

Reading:

mL of NaOH added pH

0 Initial pH: _______

(continued)

mL of NaOH added pH

Constructing a Titration Curve: Open Microsoft Excel. In the first column, enter the amount of base you added (This is equal to the Burette

Reading – Initial Reading).

In the second column, enter each corresponding pH reading.

Create a scatter plot of the amount of base added vs. the pH. Include a title and axes labels. Don’t add a smooth

curve.

Print out a copy for each group member.

Clean up: Put any leftover acid in the acid waste container.

Put any leftover base in the base waste container.

Put the titrated chemicals in the neutral waste container.

Wash all glassware.

Titration Lab Skills Checklist:

1. Correctly read a meniscus.

Level: Needs Improvement ________ Proficient ________ Exemplary ________

2. Know the lab materials and safety equipment for this lab.

Level: Needs Improvement ________ Proficient ________ Exemplary ________

3. Know the procedure of the lab.

Level: Needs Improvement ________ Proficient ________ Exemplary ________

4. Use and interpret indicators (pH paper and cabbage juice).

Level: Needs Improvement ________ Proficient ________ Exemplary ________

5. Collect, organize, and graph data.

Level: Needs Improvement ________ Proficient ________ Exemplary ________

6. Formulate conclusions of the experiment.

Level: Needs Improvement ________ Proficient ________ Exemplary ________

pH of Household Products Lab Source: http://teachers.ausd.net/classlink/getfile.ausd?fileid=45821

Introduction: Many kinds of solutions must be tested to determine whether they are acidic, basic, or neutral. The pH scale represents the

hydronium ion concentration of a solution and is used to indicate how acidic or basic a solution is. The normal pH range is

from acidic pH 1 to neutral pH 7 to basic pH 14. The most accurate method of pH determination is by use of an electronic

instrument known as a pH meter. For simpler, though less accurate pH determinations, pH indicators are commonly used.

Indicators are organic compounds that change color with changing pH. Some indicators are mixtures of compounds, each

of which changes color at a different pH. In part I, you will observe the variation in color with pH of a natural indicator. In

part II, you will use the same natural indicator to determine the pH of various household products.

Materials:

Cabbage juice, Buffers (pH 1-14), 8 test tubes, pH

meter, household products

Safety: Wear safety goggles and aprons.

Objective:

1. Observe the color of cabbage juice in solutions with pH ranging from 1-14

2. Determine the approximate pH of household products using cabbage juice

3. Determine the pH of household products using a pH meter

4. Determine whether the household products are acidic, basic, or neutral

Procedure:

Part I:

1. Observe the colors of the cabbage juice in the test tubes labeled pH 1-14 and record the colors in table 1. This will be

used as a reference.

Part II:

2. Add approximately 2 mL of the household products into 8 labeled test tubes.

3. Add approximately 2 mL of cabbage juice into the above test tubes.

4. Observe and record the colors of the solutions in table 2.

5. Compare the colors of the products with the cabbage juice to the colors from table 2 and determine the approximate

pH of your products.

6. Test the pH of each of the household products using a pH meter. Record in table 2.

Part I

pH

1

pH

2

pH

3

pH

4

pH

5

pH

6

pH

7

pH

8

pH

9

pH

10

pH

11

pH

12

pH

13

pH

14 Color of

Cabbage

juice

Part II

Product Name Milk Lemon

Juice Aspirin Shampoo Bleach Windex Coca-Cola

Dishwashin

g Soap

Color of

Product &

Cabbage Juice

Approximate

pH

pH using pH

meter

Page 1

Post-Lab Questions

1. What are the advantages and limitations of using an acid-base indicator such as cabbage juice to test the pH of

household products?

2. How do the pH values obtained from the cabbage juice compared with the one obtained from the pH meter? Explain

any discrepancy.

3. Draw a pH scale (1-14) and place the products at the appropriate pH.

4. Which products are acidic? Basic? Neutral? Explain your reasoning.

5. Which product contains the highest concentration of hydrogen ions? Lowest? Explain your reasoning.

6. Many commercial products are advertised as pH balanced. Explain what is meant by the term “pH balanced”?

7. Normal rain has an approximate pH of 5 whereas acid rain has an approximate pH of 3. Acid rain is how many times

more acidic than normal rain? Explain.

Page 2

Conclusion:

Summarize the results of the experiment. List possible sources of errors and suggest ways to improve the

accuracy/precision of the results.

Page 3

Name: _____________________

pH Exit Slip

1. _____ To mix acids and bases to cancel each other out and make salt water.

2. _____ A compound that adds H+ ions to water.

3. _____ Equal number of H+ and OH- ions; water is an example.

4. _____ A compound that adds OH- ions to water.

5. _____ When caused by pollution (pH < 5.6).

A. Acid B. Base C. Neutral D. Neutralize E. Acid Rain

Name: ______________________

Titrations Quiz

Balance this neutralization reaction:

_____ H2SO4 + _____ KOH _____ K2SO4 + _____ H2O

What is the difference between the endpoint and the equivalence point of a titration?

Solution A (pH 4); Solution B (pH 2)

Which has more H+ ions?

Which has less OH- ions?

Name: ______________________

Indicators Quiz

What is the purpose of an indicator?

What is a Universal Indicator?

How is using an indicator different than using a pH probe?