Lesson Notes By Weeks and Term - Senior Secondary 2

Acid Base Reaction I

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TERM׃ 1ST TERM

WEEK NINE

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:        

Subject: Chemistry

Topic: ACID BASE REACTION 1

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Define acid base reaction.
  2. Discuss the types of qualitative analysis.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher introduces the acid base reaction to the students.

 

Students pay attention

STEP 2

EXPLANATION

Teacher explains the types of qualitative analysis.

Students pay attention and participates

STEP 3

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

ACID BASE REACTION

An acid-base reaction involves the transfer of protons (H+ ions) between substances. Acids donate protons, while bases accept them. The resulting products are often water and a salt. Example: HCl (acid) + NaOH (base) → H2O + NaCl (salt).

An acid dissociates onto H+ and lower pH while a base dissociates into OH- and raises the pH. Buffers can absorb the excess ion to maintain pH.

Ionization of water.

Hydrogen ions are spontaneous generated into pure water by the dissociation (Ionization) of a small percentage of water molecules into equal number of hydrogen(H+) and hydroxide (OH-) ions.

The hydroxide ion remains in the solution because of their hydrogen bond with the water molecules; the hydrogen ions consisting of naked protons are immediately attracted to the un-ionized water molecules and form hydronium ions (H3O+).

By convention, scientist refer to hydrogen ions and their concentration as they were free in this state in liquid water.

2H2O      H3O+ + OH-

The concentration of the hydrogen ions dissociating from pure water is 1 x 10-7 moles H+ ions per liter of water. The pH is calculated as the negative of the logarithm of the concentration:

pH = - log[H+]

The negative log of 1 x 10-7 is equal to 7.0, which is also known as neutral pH. Human cells and blood each maintain near neutral pH.

PH scale

The acidity and alkalinity of substances are measured using a scale of numbers from 0 to 14, called the pH scale. A solution with a pH value of 7 is neutral, i.e, neither acidic nor alkaline. A solution with a pH value less than 7 is acidic, while one with a value more than 7 is alkaline. Acidity increases with decreasing pH value, while alkalinity increases with increasing pH values.

Acid base indicators

Acid base indicators are dyes which change colour according to the pH of the medium. Litmus is a common indicator which is red in acid and blue in alkali. It's changes from red to purple to blue in alkali over a pH range of 5.0 to 8.0, phenolphthalein (colorless in acidic and pink in basic solutions), and bromothymol blue (yellow in acidic and blue in basic solutions). Each indicator has its own specific pH range over which it changes colour.

Measuring pH of a solution.

The pH of a solution may be measured by

- universal indicator and the

- pH meters.

Indicators and their pH ranges:

  1. Litmus Paper:

   - Red Litmus: pH 4.5 - 7

   - Blue Litmus: pH 8 - 9.5

  1. Universal Indicator:

   - pH 0-3: Strong acid

   - pH 4-6: Weak acid

   - pH 7: Neutral

   - pH 8-11: Weak base

   - pH 12-14: Strong base

  1. Phenolphthalein:

   - pH 8.2 - 10 (Colorless below pH 8.2, pink above pH 10)

  1. Bromothymol Blue:

   - pH 6 - 7.6 (Yellow below pH 6, blue above pH 7.6)

NOTE: Colors may vary slightly depending on factors like concentration and the specific conditions of the solution.

Acid base Titration

 Titration is a laboratory technique used to determine the concentration of a solution by reacting it with a solution of known concentration. In acid-base titrations, an acid or base of known concentration (titrant) is slowly added to a solution of the substance being analyzed (analyte) until the reaction is complete.

The point at which the reaction is just complete is called the equivalence point, and it's often detected using an indicator or a pH meter- the best indicator being the universal indicator. The change in the pH during the course of the titration depends on the strength of the acid and the alkali used.

Some of the instrument during acid base titration and precautions in using some of them.

  1. Weighing bottle
  2. Chemical balance
  3. Pipette
  4. Burette
  5. Retort stand
  6. Filter paper
  7. Funnel
  8. White tile
  9. Standard volumetric flask
  10. Conical flask.

Precautions in using pipette, burette and conical flask.

A. Pipette

  1. Rinse the pipette with the solution it should be used to measure, i.e, base.
  2. Avoid bubbles in the pipette
  3. Make sure the mark to read is the level with your eyes.
  4. Do not blow the last drop

B. Burette

  1. Rinse the burette with acid or allow it to drain after rinsing with distilled water.
  2. Make sure the burette jet is filled.
  3. Avoid air bubbles.
  4. Make sure the burette is not leaking.
  5. Take your burette readings with your eyes at the same level as the meniscus to avoid error due to parallax.
  6. Remove the funnel before taking your reading.

C. Conical flask

  1. Do not rinse it with any of the solution to be used for titration except distilled water.
  2. Wash down with distilled water any drop of the solution that stick by the sides of the conical flask during titration.

EVALUATION: - Discuss acid base reaction.

                         -  How is water ionized?

                        -  Identify the common indicators used for determining the pH of a solution and their pH range.

                        - What acid base titration?

                       - Identify 5 instruments used during acid base titration.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively