IB Chemistry R3.1.13 Ph Curves of Acid-base Combinations Notes

Key Features of pH Curves

Before diving into specific examples, let’s define the key features of a pH curve:

Intercept with the pH axis:

This represents the initial pH of the solution, determined by the strength and concentration of the analyte (the substance being titrated).

Equivalence point:

The point where the moles of acid equal the moles of base added.
The pH at this point depends on the strength of the acid and base.

Buffer region:

A relatively flat section of the curve, observed in titrations involving weak acids or bases, where the solution resists changes in pH.

Points where $ \text{pH} = \text{pKa} $ or $ \text{pOH} = \text{pKb} $:

These occur halfway to the equivalence point in weak acid-base titrations and are critical for identifying the acid/base strength.

Tip

To identify the equivalence point on a pH curve, look for the steepest section of the graph where the pH changes rapidly.

Note

For the acid-base reactions outlined below, keep in mind that the opposite processes can occur.
For instance, instead of adding a strong acid to the weak base, you can add a weak base to a strong acid.
Correspondingly, the way the pH graph looks will change as well.

Strong Acid + Strong Base

The curve starts at a low initial pH (around 1 or lower for a 0.1 M strong acid) because strong acids like HCl or $\text{HNO}_3$ fully dissociate, producing a high concentration of $\text{H}^+$ ions.

The pH rises gradually at first, then increases sharply near the equivalence point.

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IB Chemistry R3.1.13 Ph Curves of Acid-base Combinations Notes

General Shapes of pH Curves

Key Features of pH Curves

Strong Acid + Strong Base

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General Shapes of pH Curves

Key Features of pH Curves

Strong Acid + Strong Base

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry R3.1.13 Ph Curves of Acid-base Combinations Notes

General Shapes of pH Curves

Key Features of pH Curves

Strong Acid + Strong Base

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Unlock the rest of this chapter with a free account

General Shapes of pH Curves

Key Features of pH Curves

Strong Acid + Strong Base

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

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Unlock the rest of this chapter with a free account

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics