Define (i) an acid, (ii) a base - Leaving Cert Chemistry - Question 9 - 2019

The pH is defined as:

$pH = - ext{log} [H^+]$

where [H extsuperscript{+}] is the concentration of hydrogen ions in moles per liter.

The completed equation is:

$pH + pOH = 14$

The pOH can be calculated using the relationship between pH and pOH:

$pOH = 14 - pH = 14 - 7 = 7$

To calculate the pH of a sodium hydroxide (NaOH) solution, we first determine the pOH:

NaOH is a strong base and completely dissociates to provide hydroxide ions:

$[OH^-] = 0.01 ext{ M}$

Using the relationship:

$pOH = - ext{log} [OH^-] = - ext{log} (0.01) = 2$

Now, we can calculate the pH:

$pH = 14 - pOH = 14 - 2 = 12$

During the flocculation stage, suspended particles clump together to form larger aggregates, or flocs, which can then be more easily removed from the water.

The purpose of chlorinating the water supply is to kill microorganisms, such as bacteria and pathogens, to sterilize the water and prevent it from becoming re-contaminated after purification.

Fluorine compounds are added to the water to prevent tooth decay and strengthen tooth enamel.

When the pH of the water is too low, a base such as lime (Ca(OH) extsubscript{2}) is added to raise the pH to a more neutral level.