Acid-Base Titrations

Concept Presentation byPooja Sharma

Rajni Kant Sharma(13/07/12)

ACID 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.

DEFINITIONS OF ACID AND BASES Vante Arrhenius- acids produce H+ ions in aqueous solutions- bases produce OH- ions in aqueous solutions

Johannes Nicolaus Brønsted - Thomas Martin Lowry

- acids are proton donors- bases are proton acceptors

Gilbert Newton Lewis- acids are electron pair acceptors- bases are electron pair donors

NEUTRALIZATION REACTIONS

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 chlorideThis process is known as Neutralization Reaction. 

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:

Brainstorm activity by whole class Mini-lecture method Model lab Lab activity by whole class Assignment on lab Teacher lab/ demonstrations, watching videos,

gizmos and use of other online resources. 

VIDEO DEMONSTRATION ON ACID BASE TITRATION

http://www.youtube.com/watch?v=TcAdpVzTSlg

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.

LESSON SEQUENCES

Lesson 1: Acid and BasesProperties and their reactions Lesson 2: NeutralizationProcess of neutralization with reactions Lesson 3: pH valueDefinition, Role and Importance of pH

value

Lesson 4: TitrationRole of most common types of qualitative acid-base titrations  Lesson 5: Demonstration of acid –base titrationBy 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 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.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 at the 0 ml mark. •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. The solution turns pink.

•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. Record the final reading when pick colour disappears.

•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

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. [Chem. Educ. Res. Pract., 2006, 7 (1), 32-45]

DIFFERENTIATED ASSESSMENT STRATEGIES

(SOLUTIONS TO STUDENT’S DIFFICULTIES)

Assessment & Evaluation

ELL student accommodations

Special needs student accommodations

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.

•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://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/

PatrickSchwarzListActivity2.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