Which of the following has the greatest concentration of hydrogen ions? How is this determined?

Human blood at pH 7
Baking soda at pH 9
Black coffee at pH 5
Household ammonia at pH 11
Cola at pH 3

1 Answer
Paul G. · Ernest Z.
Aug 30, 2016

Cola (pH 3)

Explanation:

pH is a shorthand numerical value that represents the concentration of hydrogen ions in solution.

The scale 0-14 represents the usual range of possible concentrations of protons (H+) in an aqueous system.

We can consider H+ to mean the same as H3O+ (a water molecule carries
the H+).

pH is the negative log of hydrogen ion concentration, meaning that:

pH=−log[H3O+]=−log[H+]

and therefore:

10−pH=[H+]
10−3=1.0×10−3lmol/L

Let's simplify:

pHm[H+](mol/L)
ll3mml1×10−3
ll5mml1×10−5
ll7mml1×10−7
ll9mml1×10−9
l11mm1×10−11

This is counter-intuitive without the background information (i.e. the negative log) but, as you increase pH, you decrease the concentration of H+.

As you decrease the pH, you increase the concentration of H+.

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