Question

Explain why the pH scale is a convenient tool to measure the acidity or basicity of a substance.

The definition for acids and bases provided in the introduction to this experiment is called theBronsted-Lowry formulation. Another formulation, that of Arrhenius, defines an acid as a speciesthat supplies H+ to solution and a base as something that supplies OH- to solution. Whichexplanation is more inclusive than the other, and why?

Answer 1

Solutions with a pH less than seven are acidic. Solutions with a pH greater than seven are basic. If a solution has a pH exactly equal to seven, it is neutral.

It's possible to discover the pH of a solution by using compounds known as "indicators."

Indicators are compounds that change colors as the pH of the solution changes.

The two most commonly used indicators are litmus (red in acid and blue in base) and phenolphthalein (colorless in acid, pink in base).

Strong acids are acids that very nearly completely dissociate when you put them into water.

That is, almost every molecule of the acid HA that's placed into water breaks up completely to form H⁺ and A^- ions.

Some common strong acids include HCl, HBr, HI, HNO₃, and HClO₄.

Weak acids are acids that only dissociate to a small degree in water.

As a result, when we place weak acids in water, the H⁺ concentration is not the same as the original concentration of the acid.

We can use our knowledge of aqueous equilibria (Solution Chemistry/emical Equilibria) to find the acid concentration.

What's the pH of a 0.050 M LiOH solution?

• K_w = [H⁺][OH^-]
• 1.00 × 10^-14 = [H⁺][0.0500]
• [H⁺] = 2.00 × 10^-13 M

To find pH, we simply use the equation:

• pH = -log[H⁺]
• pH = -log[2.00 × 10^-13]
• pH = 12.7

This answer indicates a very basic solution.

Hence Arrhenius explanation than the other to measure pH values.