Acid-Base Titrations
Rajni Kant Sharma
Pooja Sharma
(13/07/12)
1
Background information of Acid –Base Titration
Acids and bases
Acids and bases are chemical compounds that have distinctive
properties in water solution. The sour taste of a lemon, lime, or
grapefruit, for example, is caused by citric acid. The slippery feel of
ammonia, a common base, is characteristic of all bases. Bases tend to
taste bitter. Acids and bases also change the color of certain dyes, such
as phenolphthalein and litmus. Acids change litmus treated paper from
blue to red. Acids change basic phenolphthalein from red to colorless.
Bases change litmus treated paper from red to blue and phenolphthalein
from colorless to pink.
Neutralization
Acids and bases are sometimes described as the chemical opposites of
each other .Acids and bases neutralize the action of each other. This is
why we take antacids for stomach-aches, because the antacid is a base,
and neutralizes the increased concentration of an acid in the stomach.
If equivalent quantities of an acid and a base are combined, the two
compounds react to form a salt and water.
For example:
HCl(aq)
+ NaOH(aq) → NaCl(aq)
+ H2O(l)
hydrochloric
sodium
sodium
water
acid
hydroxide
chloride
This process is known as neutralization.
2
pH ( Power of hydrogen)
Acidity and alkalinity of the substance depends upon its pH value. The
pH is the concentration of hydrogen ions in solutions.
Numerically, pH is defined as the negative logarithm of the hydronium
ion concentration to the base 10
i.e. pH = - log10 [H3O+]
If pH < 7, then the substance is an acid.
If pH > 7, then the substance is a base.
If pH = 7, then the substance is neutral.
Titration
Titration is a common laboratory technique used to determine the
concentration of substances in solution. It’s a process in which
one solution is added to another solution such that it reacts under
conditions in which the added volume may be accurately measured.
Titrations are most commonly associated with acid-base reaction, but
they may involve other types of reactions as well.
Advance Preparation for Acid-Base Titrations
 Review safety procedures.
 Collect all the materials required.
 The teacher should do the demonstration himself/herself before
doing it with the students.
 Remember to add Acid to Water not Water to Acid.
Teaching Learning Strategies
Any of the following strategies can be used interactively with the class
to build in student accountability for learning
3
Brainstorm activity by whole class
 Divide class into groups of 3-4.
 Pre-lab activity by the teacher and check students’ prior knowledge
about the topic ‘Acids and Bases and their Properties’ by
brainstorming.
 Make connections to real life situations, for example, acidic foods and
drinks are harmful for teeth so avoid pops and sour candies and also
applications of acids and bases, such as vinegar is used in pickled
vegetables.
 Each group orally presents selected pre-lab questions without
repeating answers of other groups.
Mini-Lecture method
 Point out dangers associated with each chemical (MSDS related
information), proper disposal method, and general safety information.
 Use molecular models or computer animations to illustrate splitting
into ions for Arrhenius’ theory. If not available, use Styrofoam balls
and toothpicks or small plastic building blocks. Be sure to be
consistent in your choice when representing H+ and OH-.
 To show how pH and acidity are related, carry out a mini
investigation using everyday life examples, such as shampoo, bleach,
liquid detergent etc.
Model Lab
 Demonstrate lab to students including how to set up whole apparatus
(burette on stand )
4
Lab activity by whole class
 Members of groups are given roles (time keeper/safety monitor,
reporter / recorder, facilitator, materials manager)
 Time keeper/safety monitor keeps an eye on time and makes sure lab
safety rules are being followed, materials manager retrieves/returns
materials, recorder records data and reports final data to teacher
immediately, facilitator assists and makes sure everyone participates).
 Students to wash lab equipment and clean lab bench.
 Appoint auditor roles to responsible students (one student inventories
all returned equipment; one student ensures benches are clean etc).
 Students must follow clean up rules without any relaxation before
working on lab handout.
Assignment
 Lab report.
Teacher lab/ demonstrations, watching videos, gizmos and
use of other online resources.
Curriculum Expectations
 E2. Investigate qualitative and quantitative properties of solutions,
and solve related problems.
 E2.7 Determine the concentration of an acid or a base in a solution
(e.g., the concentration of acetic acid in vinegar), using the acid–base
titration technique [PR, AI]
 E3. Demonstrate an understanding of qualitative and quantitative
properties of solutions.
5
Lesson Sequences
Lesson 1: Acid and Bases
Properties and their reactions
Lesson 2: Neutralization
Process of neutralization with reactions
Lesson 3: pH value
Definition, Role and Importance of pH value
Lesson 4: Titration
Role of most common types of qualitative acid-base titrations
Lesson 5: Demonstration of acid –base titration
By using Gizmo’s and videos
Lesson 6: Lab activity by the students with record of data and
calculations
HCl(aq)
+ NaOH(aq) → NaCl(aq)
+ H2O(l)
hydrochloric
sodium
sodium
water
acid
hydroxide
chloride
Students’ Lab Activity
Equipment and Materials
Chemical safety goggles, lab apron, large test tube, Berol pipette, test
tube rack, burette clamp, retort stand, wash bottle, burette, 100 ml
beaker, 250 mL flask, two 250 ml beakers, dropper, dilute hydrochloric
6
acid (0.1mol/L), sodium hydroxide solution (concentration unknown),
Phenolphthalein indicator,.
Safety Precautions
Before starting the titration lab, review safety precautions and perform a
quick review to check how well students are at determining the
concentration of a diluted solution from a standard solution before they
perform any calculations. The solutions of sodium hydroxide and
hydrochloric acid are both irritants. Avoid skin contact. If some does
spill on your skin, wash the affected area with plenty of cool water.
Report any spills to your teacher.
Procedure
 Prepare a data table. Record all of your experimental results in the
table as soon as you obtain them.
 Clean all glassware before you use it.
 Obtain about 120 ml of hydrochloric acid solution in a 250 ml
beaker
 To clean the burette - make sure it is closed and, using a funnel,
pour about 10 ml of the hydrochloric acid solution into the burette.
7







Place the burette in a burette holder on a retort stand and place a
catch beaker under the spout of the burette and let the hydrochloric
acid run through. Repeat this procedure twice more using new 10
ml samples of hydrochloric acid each time.
Refill the burette so that the meniscus of the hydrochloric acid
solution is above the 0 ml mark and let the excess solution run out
so that the meniscus eventually rests on the 0 ml mark. If there is a
drop of solution hanging on the burette tip, remove it by touching
the drop to the inside wall of the 250 ml flask.
Obtain 120 ml of sodium hydroxide in another (clean!) 250 ml
beaker.
Pipette 25 ml of the sodium hydroxide into the flask.
Place 3 drops of phenolphthalein into the flask that contains the
base.
Place the flask under the burette.
Slowly add hydrochloric acid from the burette, one ml at a time.
Stop after every 1 ml addition to swirl the solution in order to
make sure that the acid is properly mixed with the base. You will
start to see the pink color change. When you get the sense that you
are getting close to the endpoint add the acid drop by drop and
swirl continuously so that you don’t miss it. The endpoint has been
reached (or passed) when the indicator changes color permanently.
The endpoint will occur suddenly and you may overshoot it the
first time you do the titration. If you think you passed the endpoint
by several drops redo the titration before recording the volume of
acid added.
Repeat the titration (steps 7 – 10) twice more. Do not refill the
burette unless you have run out of acid. Record the initial reading
of the burette and add acid from that point. Record all of your data.
8
Potential student’s difficulties
Acid-base titrations are common laboratory activities carried out in
high school chemistry courses. Using a series of qualitative and
computer-based tasks, this study examined sixteen American
students’ understanding of titrations. The findings indicated that
students having considerable difficulty with acid-base chemistry,
were unable to describe accurately acid-base concepts, such as pH,
neutralization, strength, and the theoretical description of acids and
bases. Further, most students could not relate the concepts to actual
solutions. Student difficulties stemmed from a lack of
understanding of some underlying chemistry, such as the nature of
chemical change and the particulate nature of matter. A number of
factors were identified as contributing to these difficulties,
including the overstuffed nature of introductory chemistry itself,
the emphasis during instruction on solving numerical problems,
and the dominant role played by the textbook. The conceptual
density of acid-base chemistry, the confusing nature of acid-base
terminology and the lack of agreement about what material should
be included in the chemistry curriculum were identified as being
problematic. [Chem. Educ. Res. Pract., 2006, 7 (1), 32-45]
Differentiated assessment strategies
(Solutions to student’s difficulties)
Assessment & Evaluation
 Quiz on Acids and Bases (Knowledge/Understanding)
Pre Lab- Revise Lab Safety Rules
Formal Lab- Acid – Base Titration (Thinking/Inquiry)
9
Activity for strong and weak acids and bases (Inquiry/investigation)
Reflective Response on Demonstration (Communication)
Students’ Lab Report on Titration (Inquiry/Communication)
 Formative assessment would be completely based on student’s
contributions to last discussions during role-play and participation
in the lab.
 Culminating Task Rubric for research project and oral presentations
(Communication, Application)
 Understanding of the concepts of acid –base titration would also be
evaluated on a unit test (Knowledge/Understanding, Application,
and Communication) with emphasis on Application of the concepts
learned.
ELL student accommodations
 By having access to computers and internet, students will have
access to different translational services (e.g. Google Translate)
and explanatory dictionaries (e.g. Wiki) which will help them
understand asked requirements.
 A Teacher Assistant (if available), might be invited to help with
the activity.
 Arranging groups in such a way that ELL students can be together
with English proficient student, who can speak their language too.
 Translating or illustrating Lab safety instructions (and operating
instructions for apparatuses and reagents) with little amount of
writing.
 Simplifying the language of procedural writing.
10
Special needs student accommodations
 An educator or Teacher Assistant (if available) who have
knowledge and / or experience in dealing with special needs
students might be invited to help in the activity.
 As much as possible, creating groups such that all members feel
comfortable with each other.
 Illustrating lab safety with little amount of writing and more
pictures.
 Providing additional time
 Simplifying the language of procedural writing
Practical Applications and Societal Implications
 Softening of water using soda lime process by municipalities and
wastewater treatment.
 Neutralization has many practical applications. Reclamation
(restoration) of land once used for mining also involves
neutralization reactions
 Neutralization is also used to deal with environmental problems.
 Acids and bases are used in the manufacture of fertilizers,
synthetic fabrics, pigments, petroleum, iron and steel, explosives,
dyes, plastics, pesticides, soaps and detergents, paper, film, and
many other chemicals
 They are also used for various other purposes, including cleaning
surfaces, refining oil and sugar, electroplating metals, and treating
food products.
 Sulphuric acid is the most widely used chemical in industry.
11
 Nitric acid, another important industrial acid, is used in the
manufacture of fertilizers, plastics, photographic film, and dyes
and explosives as dynamite and TNT.
 Hydrochloric acid is used to clean metals, brick and tile; it is used
in the manufacture of sugar and glue.
 pH plays an important role in biological reactions.
References
http://www.scienceclarified.com/A-Al/Acids-and-Bases.html
http://www.okstate.edu/jgelder/acidPage25.html
http://jseguin.weebly.com/solutions-and-solubility.html
wlouischemgrade12.wikispaces.co / Solutions + and + Solubility + SC
http://specialed.about.com/od/teacherstrategies/a/differentiated.htm
http://preparatorychemistry.com/Bishop_Titration.htm
http://www.isbe.net/assessment/pdfs/ell_guidance.pdf
http://www.teachervision.fen.com/special-education/resource/5347.html
http://www.spectrumtrainingsystemsinc.com/files/PatrickSchwarzListAc
tivity2.pdf
http://chemistry.about.com/od/chemistryquickreview/a/titrationcalc.htm
http://www.youtube.com/watch?v=XnHH-pXqqRs
http://www.youtube.com/watch?v=TcAdpVzTSlg
12