ACID BASE TITRATION

BY – VISHAL SINGH SOLANKI

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CONTENT

• INTRODUCTION
• ACID
• BASE
• TERMINOLOGY
• TYPES OF ACID BASE TITRATION
• TITRATION CURVE
• SUMMERY

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INTRODUCTION TO TITRATION

• a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration flask.
• A burette is used to deliver the second reactant to the flask.
• An indicator or pH Meter is used to detect the endpoint of the reaction.

INTRODUCTION

• An acid–base titration is a method of quantitative analysis for determining the concentration of an acid or base by exactly neutralizing it with a standard solution of base or acid having known concentration. A pH indicator is used to monitor the progress of the acid–base reaction.

Alkalimetry and acidimetry

• Alkalimetry and acidimetry are a kind of volumetric analysis in which the fundamental reaction is a neutralization reaction.
• Acidimetry is the specialized analytic use of acid-base titration to determine the concentration of a basic (synonymous to alkaline) substances using standard acid.
• Alkalimetry, is the same concept of specialized analytic acid-base titration, but for an acidic substance using standard base.

ACID

• A strong acid dissociates (or ionizes) completely in aqueous solution to form hydronium ions (H3O+)

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• A weak acid does not dissociate completely in aqueous solution to form hydronium ions 

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BASE

• A strong base dissociates completely in aqueous solution to form hydroxide ions (OH-)

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• A weak base does not dissociate completely in aqueous solution to form hydroxide ions (OH-)

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Examples of weak/strong acids and bases

CONTI…

• Weak acids and weak bases always exist as conjugate acid-base pairs in an aqueous solution as represented below

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• Here, HA is the acid and A-, termed as the conjugate base of HA

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• In the above reaction, A- base and HA is the conjugate acid of A-

RULE OF THUMB

• Rule of thumb is: Weak acids have strong conjugate bases, while weak bases have strong conjugate acids. As shown in the above two reactions, if HA is a weak acid, then its conjugate base A- will be a strong base. Similarly, if A- is a weak base, then its conjugate acid HA will be a strong acid.

TERMINOLOGY USED IN TITRATION

1. Titration – A process where a solution of known strength is added to a certain volume of a treated sample containing an indicator.
2. Titrant – A solution of known strength of concentration used in the titration.
3. Titrand/Analyte – The titrand is any solution to which the titrant is added and which contains the ion or species being determined.
4. Titration curve – A plot of pH Vs millilitres of titrant showing the manner in which pH changes Vs millilitres of titrant during an acid-base titration.
5. Equivalence point – The point at which just adequate reagent is added to react completely with a substance.
6. Endpoint - refers to the point at which the indicator changes color in an acid-base titration.
7. Buffer solution – A solution that resists changes in pH even when a strong acid or base is added or when it is diluted with water.

Types of Acid-Base Titration

• The types and examples of strong/weak acids and bases are tabulated below.

What is a titration curve?

• A titration curve is the plot of the pH of the analyte solution versus the volume of the titrant added as the titration progresses.
• In a titration, the equivalence point is the point at which exactly the same number of moles of hydroxide ions have been added as there are moles of hydrogen ions. In a titration, if the base is added from the burette and the acid has been accurately measured into a flask. The shape of each titration curve is typical for the type of acid-base titration.

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Choice of Indicators

• Acid-base indicators are substances which change colour or develop turbidity at a certain pH. They locate equivalence point and also measure pH. They are themselves acids or bases are soluble, stable and show strong colour changes. They are organic in nature.
• A resonance of electron isomerism is responsible for colour change. Various indicators have different ionization constants and therefore they show a change in colour at different pH intervals.
• Acid-base indicators can be broadly classified into three groups.
• The phthaleins and sulphophthaleins (eg; Phenolphthalein)
• Azo indicators (eg; Methyl orange)
• Triphenylmethane indicators (eg; Malachite green)

CONTI…

• The two common indicators used in acid-base titration is Phenolphthalein and methyl orange.
• In the four types of acid-base titrations, the base is being added to the acid in each case.
• A graph is shown in next slide where pH against the volume of base added is considered.
• The pH range over which the two indicators change colour.
• The indicator must change within the vertical portion of the pH curve.�

CHOICE OF INDICATOR

EXPERIMENT OF ACID – BASE TITRATION

To summarize

• In an acid-base titration, a known volume of either the acid or the base (of unknown concentration) is placed in a conical flask.
• The second reagent (of known concentration) is placed in a burette.
• The reagent from the burette is slowly added to the reagent in the conical flask.
• A titration curve is a plot showing the change in pH of the solution in the conical flask as the reagent is added from the burette.

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A titration curve can be used to determine:

1. The equivalence point of an acid-base reaction (the point at which the amounts of acid and of base are just sufficient to cause complete neutralization).
2. The pH of the solution at equivalence point is dependent on the strength of the acid and strength of the base used in the titration.

-- For strong acid-strong base titration, pH = 7 at equivalence point

-- For weak acid-strong base titration, pH > 7 at equivalence point

-- For strong acid-weak base titration, pH < 7 at equivalence point

REFERENCE

• https://courses.lumenlearning.com/introchem/chapter/acid-base-titrations/
• https://www.khanacademy.org/test-prep/mcat/chemical-processes/titrations-and-solubility-equilibria/a/acid-base-titration-curves
• https://en.wikipedia.org/wiki/Acid%E2%80%93base_titration#:~:text=An%20acid%E2%80%93base%20titration%20is,of%20the%20acid%E2%80%93base%20reaction.
• https://byjus.com/chemistry/acid-base-titration/

THANK YOU