1. Acids/base list
Acids
0 - Hydrochloric Acid (HCl)
1.0 - Battery Acid (H2SO4 sulfuric acid)
2.0 - Lemon Juice
2.2 - Vinegar
3.0 - Apples
4.0 - Wine and Beer
4.5 - Tomatoes
6.6 - Milk
Neutral
7.0 - Pure Water
Bases
7.4 - Human Blood
8.3 - Baking Soda (Sodium Bicarbonate)
10.5 - Milk of Magnesia
11.0 - Ammonia
12.4 - Lime (Calcium Hydroxide)
13.0 - Lye
14.0 - Sodium Hydroxide (NaOH)
pH is a logarithmic measure of the hydrogen ion concentration of an aqueous solution:
pH = -log[H30+
]
log is the base 10 logarithm and [H30+
] is the hydrogen ion concentration in moles per liter
The term "pH" was first described by Danish biochemist Søren Peter LauritzSørensen in 1909. pH
is an abbreviation for "power of hydrogen" where "p" is short for the German word for
power, potenz and H is the element symbol for hydrogen.
Question: Is a Negative pH Possible?
Is it possible to have a negative pH value? If you are given the molarity of hydrogen ions of an
acid that is greater than one, you'll calculate a negative pH value for the acid. Can that really
happen? Here's the answer.
Answer: It's definitely possible to calculate a negative pH value. On the other hand, whether or
not an acid actually has a negative pH value isn't something you can verify very well in the lab.
Any acid that yields a concentration of hydrogen ions with a molarity greater than 1 will be
calculated to have a negative pH. For example, the pH of 12M HCl is calculated to be -log(12) = -
1.08. However, you can't just dip a glass pH electrode in the HCl and measure a negative pH.
Glass pH electrodes suffer from a defect called 'acid error' which causes them to measure a higher
pH than the real pH. It is very difficult to apply a correction for this defect to obtain the true pH
value.

2. Also, strong acids do not fully dissociate at high concentrations. In the case of HCl, some of the
hydrogen would remain bound to the chlorine, so in this respect the true pH would be higher than
the pH you would calculate from acid molarity.
To further complicate the situation, the activity or effective concentration of hydrogen ions in a
concentrated strong acid is higher than the actual concentration. This is because there is so little
water per acid unit. While pH commonly is calculated as -log [H+
] (negative of the logarithm of the
hydrogen ion molarity), it would be more accurate to write pH = - log aH+
(negative pf the
logarithm of the hydrogen ion activity). This effect of the enhanced hydrogen ion activity is very
strong, and makes the pH much lower than you'd expect from the acid molarity.
So... you can't accurately measure extremely low pH with a glass pH electrode and it is difficult to
tell whether the pH is lowered by the increased hydrogen ion activity more than it is raised by
incomplete dissociation. Negative pH is possible, but not something you can show.
The pH scale usually runs from 0 to 14, but you can calculate a negative pH value for 12 Mstrong
acid. Of course, calculating a negative pH is different from an aqueous solution actuallyhaving a
negative pH. It turns out experimental verification of negative pH values is slightly complicated.
You can't use a glass pH meter to get an accurate pH measurement under extremely acidic
conditions. The glass meter will give a high reading for which you can't apply some standard
correction. Even strong acids don't completely dissociate at high concentrations, so a concentrated
strong acid might be expected to have a higher pH than you would calculate. On the other hand,
the hydrogen ion activity is higher for a concentrated strong acid than for a more dilute solution,
giving the pH a lower value than you would calculate. Which has more of an effect... the
incomplete dissociation or the increased hydrogen ion activity? I'm not sure it's possible to say,
but if the hydrogen ion activity wins out, the acid could have a negative pH.