The Notes: Which substances will have a higher hydrogen ion concentration?

Monday, May 10, 2010

Which substances will have a higher hydrogen ion concentration?

The pH Scale

The graphic that you attached is an illustration of the pH scale.

Substances that have pH numbers less than 7 are acids. Acids tend to disassociate into $\displaystyle~{{H}}^{+}$ ions and negatively charged anions when dissolved in water. The lower the pH number, the stronger the acid.

Pure water has a pH of 7. It is considered neutral. The concentration of $\displaystyle~{{H}}^{+}$ ions and $\displaystyle~{O}{{H}}^{{-{}}}$ ions in water is equal.

Substances that have pH numbers greater than 7 are bases. Bases tend to disassociate into positively charged cations and $\displaystyle~{O}{{H}}^{{-{}}}$ ions when dissolved in water. The higher the pH number, the stronger the base.

Calculating pH

The pH of a substance is a measure of the concentration of $\displaystyle~{{H}}^{+}$ ions.:

pH = -log[ $\displaystyle~{{H}}^{+}$ ]

The square brackets around the $\displaystyle~{{H}}^{+}$ stand for "the concentration of."

Calculating [ $\displaystyle~{{H}}^{+}$ ]

[ $\displaystyle~{{H}}^{+}$ ] ions can be calculated by rearranging the above formula to:

[ $\displaystyle~{{H}}^{+}$ ] = $\displaystyle~{{10}}^{{-}}^{{p}}^{{H}}$

The [ $\displaystyle~{{H}}^{+}$ ] for battery acid (pH 1) would be:

$\displaystyle~{{10}}^{{-}}^{1}$ = 0.1 M

The [ $\displaystyle~{{H}}^{+}$ ] for lye (pH 13) would be:

$\displaystyle~{{10}}^{{-}}^{13}$ = 1 x $\displaystyle~{{10}}^{{-}}^{13}$ M

Therefore, the lower a substance's pH, the higher the [ $\displaystyle~{{H}}^{+}$ ].

The order of substances from highest to lowest [ $\displaystyle~{{H}}^{+}$ ] is: battery acid, lemon juice, wine, normal rain, distilled water, baking soda, soft soap, ammonia, lye.

The Notes

Monday, May 10, 2010

Which substances will have a higher hydrogen ion concentration?

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