IB Chemistry Topic R3.1.9 Poh Scale Revision Notes (HL)

IB Chemistry Topic R3.1.9 Poh Scale Revision Notes (HL) | RevisionDojo

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The pOH Scale and Its Relationship with pH

The pOH scale, like the pH scale, is logarithmic.
However, instead of measuring the concentration of hydrogen ions $ [H^+] $, it measures the concentration of hydroxide ions $ [OH^-] $.
The pOH of a solution is defined by the formula: $$\text{pOH} = -\log_{10}[\text{OH}^-]$$
Here, $ [OH^-] $ represents the molar concentration of hydroxide ions.

Note

This formula allows us to express very small concentrations of $ [OH^-] $ as manageable numbers.

Example

A solution with $ [OH^-] = 1 \times 10^{-3} \, \text{mol dm}^{-3} $ has a pOH of:

$$\text{pOH} = -\log_{10}(1 \times 10^{-3}) = 3$$

Tip

The pOH decreases as the hydroxide ion concentration, $ [OH^-] $, increases, because $\text{pOH} = -\log_{10}[\text{OH}^-]$.
As $ [OH^-] $ increases, the pOH decreases.

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The pOH Scale and Its Relationship with pH

The pOH scale, like the pH scale, is logarithmic.
However, instead of measuring the concentration of hydrogen ions $ [H^+] $, it measures the concentration of hydroxide ions $ [OH^-] $.
The pOH of a solution is defined by the formula: $$\text{pOH} = -\log_{10}[\text{OH}^-]$$
Here, $ [OH^-] $ represents the molar concentration of hydroxide ions.

Note

This formula allows us to express very small concentrations of $ [OH^-] $ as manageable numbers.

Example

A solution with $ [OH^-] = 1 \times 10^{-3} \, \text{mol dm}^{-3} $ has a pOH of:

$$\text{pOH} = -\log_{10}(1 \times 10^{-3}) = 3$$

Tip

The pOH decreases as the hydroxide ion concentration, $ [OH^-] $, increases, because $\text{pOH} = -\log_{10}[\text{OH}^-]$.
As $ [OH^-] $ increases, the pOH decreases.

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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 R3.1.9 Poh Scale Notes

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

The pOH Scale and Its Relationship with pH

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The pOH Scale and Its Relationship with pH

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