Potentiometric titration curve of strong acid weak base
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indicator changes color in an acid-base titration.
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.

Titration curve chart
Let’s attempt to draw some titration curves now.
1) Titration of a strong acid with a strong base
Suppose our analyte is hydrochloric acid HCl (strong acid) and the titrant is sodium hydroxide NaOH (strong base). If we start plotting the pH of the analyte against the volume of NaOH that we are adding from the burette, we will get a titration curve as shown below.

Titration curve of a strong acid with a strong base
Point 1: No NaOH added yet, so the pH of the analyte is low (it predominantly contains H_{3}3O^\text{+}+ from dissociation of HCl).

Diagram of solution transformation prior to titration
As NaOH is added dropwise, H_{3}3O^\text{+}+slowly starts getting consumed by OH^\text{-}-produced by dissociation of NaOH. Analyte is still acidic due to predominance of H_{3}3O^\text{+}+ ions.
Point 2: This is the pH recorded at a time point just before complete neutralization takes place.
Point 3: This is the equivalence point (halfway up the steep curve). At this point, moles of NaOH added = moles of HCl in the analyte. At this point, H_{3}3O^\text{+}+ions are completely neutralized by OH^\text{-}-ions. The solution only has salt (NaCl) and water and therefore the pH is neutral i.e. pH = 7.

Diagram of solution transformation at equivalence point
Point 4: Addition of NaOH continues, pH starts becoming basic because HCl has been completely neutralized and now excess of OH^\text{-}- ions are present in the solution (from dissociation of NaOH).

Diagram of solution transformation after equivalence point
2) Titration of a weak acid with a strong base
Let’s assume our analyte is acetic acid CH_{3}3COOH (weak acid) and the titrant is sodium hydroxide NaOH (strong base). If we start plotting the pH of the analyte against the volume of NaOH that we are adding from the burette, we will get a titration curve as shown below.

Titration curve of a weak acid with a strong base
Point 1: No NaOH added yet, so the pH of the analyte is low (it predominantly contains H_{3}3O^\text{+}+ from dissociation of CH_{3}3COOH). But acetic acid is a weak acid, so the starting pH is higher than what we noticed in case 1 where we had a strong acid (HCl).

Diagram of solution transformation as titration begins
As NaOH is added dropwise, H_{3}3O^\text{+}+slowly starts getting consumed by OH^\text{-}-(produced by dissociation of NaOH). But analyte is still acidic due to predominance of H_{3}3O^\text{+}+ ions.
Point 2: This is the pH recorded at a time point just before complete neutralization takes place.
Point 3: This is the equivalence point (halfway up the steep curve). At this point, moles of NaOH added = moles of CH_{3}3COOH in the analyte. The H_{3}3O^\text{+}+ions are completely neutralized by OH^\text{-}-ions. The solution contains only CH_{3}3COONa salt and H_{2}2O.

Diagram of solution transformation at equivalence point
Hopefully it helps
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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.

Titration curve chart
Let’s attempt to draw some titration curves now.
1) Titration of a strong acid with a strong base
Suppose our analyte is hydrochloric acid HCl (strong acid) and the titrant is sodium hydroxide NaOH (strong base). If we start plotting the pH of the analyte against the volume of NaOH that we are adding from the burette, we will get a titration curve as shown below.

Titration curve of a strong acid with a strong base
Point 1: No NaOH added yet, so the pH of the analyte is low (it predominantly contains H_{3}3O^\text{+}+ from dissociation of HCl).

Diagram of solution transformation prior to titration
As NaOH is added dropwise, H_{3}3O^\text{+}+slowly starts getting consumed by OH^\text{-}-produced by dissociation of NaOH. Analyte is still acidic due to predominance of H_{3}3O^\text{+}+ ions.
Point 2: This is the pH recorded at a time point just before complete neutralization takes place.
Point 3: This is the equivalence point (halfway up the steep curve). At this point, moles of NaOH added = moles of HCl in the analyte. At this point, H_{3}3O^\text{+}+ions are completely neutralized by OH^\text{-}-ions. The solution only has salt (NaCl) and water and therefore the pH is neutral i.e. pH = 7.

Diagram of solution transformation at equivalence point
Point 4: Addition of NaOH continues, pH starts becoming basic because HCl has been completely neutralized and now excess of OH^\text{-}- ions are present in the solution (from dissociation of NaOH).

Diagram of solution transformation after equivalence point
2) Titration of a weak acid with a strong base
Let’s assume our analyte is acetic acid CH_{3}3COOH (weak acid) and the titrant is sodium hydroxide NaOH (strong base). If we start plotting the pH of the analyte against the volume of NaOH that we are adding from the burette, we will get a titration curve as shown below.

Titration curve of a weak acid with a strong base
Point 1: No NaOH added yet, so the pH of the analyte is low (it predominantly contains H_{3}3O^\text{+}+ from dissociation of CH_{3}3COOH). But acetic acid is a weak acid, so the starting pH is higher than what we noticed in case 1 where we had a strong acid (HCl).

Diagram of solution transformation as titration begins
As NaOH is added dropwise, H_{3}3O^\text{+}+slowly starts getting consumed by OH^\text{-}-(produced by dissociation of NaOH). But analyte is still acidic due to predominance of H_{3}3O^\text{+}+ ions.
Point 2: This is the pH recorded at a time point just before complete neutralization takes place.
Point 3: This is the equivalence point (halfway up the steep curve). At this point, moles of NaOH added = moles of CH_{3}3COOH in the analyte. The H_{3}3O^\text{+}+ions are completely neutralized by OH^\text{-}-ions. The solution contains only CH_{3}3COONa salt and H_{2}2O.

Diagram of solution transformation at equivalence point
Hopefully it helps
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