## pH Value

 6.2 pH Value

### The pH scale

• The pH scale is a set of number that determines the degree of acidity or alkalinity of a substance.
• The pH value would be:
• 7 for neutral substance.
• > 7 for alkaline substance ($$OH^- > H^+$$)
• < 7 for acidic substance ($$H^+ > OH^-$$$$OH^-$$)

 $$\xleftarrow[]{\textbf{Acidity } \uparrow}$$ Neutral $$\xrightarrow[]{\textbf{Alkalinity } \uparrow}$$ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

• pH: a logarithmic measurement of the concentration of hydrogen ions, $$H^+$$ contained in an aqueous solution.

 Formula for pH $$pH = -log[H^+]$$

• The concentration of hydroxide ions, $$OH^-$$ is also used to calculate the pOH value.

 Formula for pOH $$pOH = -log[OH^-]$$

 Relationship of pH with pOH \begin{aligned} pH + pOH &= 14\\ pH&=14-pOH \end{aligned}

### Hubungan nilai pH dengan kepekatan ion hidrogen dan ion hidroksida

Relationship of concentration $$H^+$$ with pH
 Concentration $$H^+$$ $$\uparrow$$, pH value $$\downarrow$$

Relationship of concentration $$OH^-$$ with pH
 Concentration $$OH^-\, \uparrow$$, pH value $$\uparrow$$

### Measurement of the pH value of a solution

• The pH value can be measured by using:

Universal indicator

• The universal indicator will change colour, and it indicates what the pH based on the colour produced is.
• The universal indicator can be found in two forms; solution or paper strips.

pH meter

• The pH meter is an instrument that is used to measure the pH value of a solution accurately.
• pH meter shows the number of the pH value in the screen.