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 `~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 `~H^+` ions and `~OH^-` ions in water is equal.

  • Substances that have pH numbers greater than 7 are bases. Bases tend to disassociate into positively charged cations and `~OH^-` 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 `~H^+` ions.:


   pH = -log[`~H^+` ]


The square brackets around the `~H^+` stand for "the concentration of."


Calculating [`~H^+` ]


[`~H^+` ] ions can be calculated by rearranging the above formula to:


   [`~H^+` ] = `~10^-^p^H`


The [`~H^+` ] for battery acid (pH 1) would be:


    `~10^-^1` = 0.1 M


The [`~H^+` ] for lye (pH 13) would be:


   `~10^-^13` = 1 x `~10^-^13` M


Therefore, the lower a substance's pH, the higher the [`~H^+` ].


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

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