There are many ways to fluoridate water. One approach is to add a salt of the fluoride ion, such as NaF. Let's calculate the pH of a 0.15 M NaF solution. (HF: Ka = 7.2 x 10-4) (a) 2 (b) 5.8 (c) 8.2 (d) 10.9 (e) 12

To calculate the pH of a NaF solution, we need to consider the dissociation of NaF in water. NaF is a salt that consists of a sodium cation (Na+) and a fluoride anion (F-). In water, the NaF salt will dissociate into its respective ions: Na+ and F-.

The fluoride ion (F-) can react with water to form hydrofluoric acid (HF) and hydroxide ions (OH-):

F- + H2O -> HF + OH-

Since HF is an acidic compound, it will partially dissociate in water, releasing hydrogen ions (H+):

HF -> H+ + F-

Now, we can calculate the concentration of HF and F- in the solution. Since we know that the initial concentration of NaF is 0.15 M, the concentration of F- is also 0.15 M. However, the concentration of HF is not the same as the concentration of F- due to the dissociation of HF.

To calculate the concentration of HF, we can use the equation for the acid dissociation constant (Ka):

Ka = [H+][F-] / [HF]

We know that the value of Ka for HF is 7.2 x 10^-4, and we can assume that the concentration of [H+] is equal to the concentration of [F-], denoted as x. The concentration of [HF] is 0.15 - x, as it is the difference between the initial concentration of NaF and the concentration of [F-].

Now, we can plug in these values into the equation for Ka:

7.2 x 10^-4 = x * x / (0.15 - x)

Solving this equation will yield the value of x, which represents the concentration of H+. Once we have the concentration of H+, we can calculate the pH using the formula:

pH = -log[H+]

After going through these calculations, we can determine the correct pH value from the given options.

Fluoridation of water is a process that involves adding fluoride to water sources in order to maintain oral health and prevent tooth decay. Fluoride ions have the ability to strengthen the tooth enamel and make it more resistant to acid attacks from bacteria. This helps to prevent the formation of cavities.

In this case, NaF is used as the source of fluoride ions. When NaF is added to water, it dissociates into Na+ and F- ions. The F- ions can then interact with water to form hydrofluoric acid (HF), which further contributes to the overall pH of the solution.

To determine the pH of the NaF solution, we need to consider the equilibrium between F- and HF. This equilibrium is governed by the acid dissociation constant (Ka) of HF. The value of Ka tells us how much HF will dissociate into H+ and F- ions.

By solving the Ka equation, we can find the concentration of H+ ions in the solution, which directly affects the pH. The pH scale measures the concentration of hydrogen ions in a solution, with lower pH values indicating high acidity and higher pH values indicating alkalinity or basicity.

In conclusion, the pH of the 0.15 M NaF solution can be calculated by determining the concentration of H+ ions using the acid dissociation constant (Ka) of HF. The correct pH value can then be identified from the given options.