pH
Definition from wiki- pH is a measure of the acidity or alkalinity of a solution. Solutions with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline). pH 7 is considered neutral because it is the pH of pure water at 25 °C. pH is formally dependent upon the activity of hydrogen ions (H+), but for very pure dilute solutions, the molarity may be used as a substitute with some sacrifice of accuracy. Because pH is dependent on activity, a property which cannot be measured easily or predicted theoretically, it is difficult to determine an accurate value for the pH of a solution. The pH reading of a solution is usually obtained by comparing unknown solutions to those of known pH, and there are several ways of doing this. The concept of pH was first introduced by Danish chemist S. P. L. Sørensen. The name, pH, has been purported to come from a variety of places including: pondus hydrogenii (Latin),potentiel hydrogène (French), and potential of hydrogen (English). However pH is actually a shorthand for its mathematical approximation: in chemistry a small p is used in place of writing - log10 and the H should more correctly be [H+], standing for concentration of hydrogen ions.
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Strong Acids- Due to the complete dissociation of strong acids in aqueous solution, the concentration of hydronium ions in the water is equal to the re-duplication of the acid introduced to solution:
[HA] = [H+] = [A−]; pH = −log[H+]
Calculate the pH of a 0.100 M solution of HCl.
Therefore, the [H+] equals 0.100 M. So, to solve it, you write:
pH = - log (0.100) = 1.000
Calculate the pH of a 1.00 M solution of HBr.
pH = - log (1.00) = 0.00 <--Answer
Strong Bases- Strong bases is pretty much the same as strong acids EXCEPT you'll be calculating a pOH first, then going to the pH.
pH + pOH = 14
Calculate the pH of a 0.100 M solution of NaOH.
Therefore, the [OH-] equals 0.100 M. So, to solve it, you write:
pOH = - log (0.100) = 1.000
pH = 14.000 - 1.000 = 13.000
Calculate the pH of a 0.050 M solution of KOH.
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Since the [OH¯] = 0.050 M (remember 100% dissociation), we have this:
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HONORS AND AP
AUTOIONIZATION of WATER
--->Auto Ionization of Water Tutorial<---
notes fromhttp://dbhs.wvusd.k12.ca.us/webdocs/AcidBase/Kw.html
H2O(l) + H2O(l) <==> H3O+(aq) + OH¯(aq)
Kw = [H3O+] [OH¯]
Kw = water autoionization constant=1.0 x 10-14 @ 25 °C
From the chemical equation just above, it can be seen that H3O+ and OH¯ concentrations are in the molar ratio of one-to-one. This means that [H3O+] = [OH¯].
Therefore the values of [H3O+] and [OH¯] can be determined by taking the square root of Kw. Hence, both [H3O+] and [OH¯] equal 1.00 x 10¯7 M in pure water.
Result #1: The pH of pure water is 7
By definition, pH = -log [H3O+]
The pH of pure water then equals -log 10¯7, which is 7.
Result #2: If the pH or the pOH is known, the other can be found.
Take the negative logarithm of each side of the Kw equation as follows:
- log Kw = -log [H3O+] + -log [OH¯]
-log 1.00 x 10¯14 = -log [H3O+] + -log [OH¯]
Note the use of the add sign on the right side of the equation. The result is ususally written as:
pKw = pH + pOH = 14
This is an extremely important equation. Learn it well.
Result #3: If the [H3O+] or the [OH¯] is known, the other can be found.
Simply divide Kw by the known value to get the other.
Suppose [H3O+] is known, then:
[OH¯] = Kw / [H3O+]
Suppose [OH¯] is known, then:
[H3O+] = Kw / [OH¯]
Result #4: If one variable ( [H3O+] or [OH¯] ) changes value (either up or down), the other variable will change in the opposite direction.
The change in values will still preserve this fundamental equality:
Kw = [H3O+] [OH¯]
Suppose [H3O+] became larger, therefore the [OH¯]
becomes smaller.
Suppose [OH¯] became larger, therefore the [H3O+] becomes
smaller.
The
acidity or alkalinity of a solution can be measured by its pH value.
True
False
Which pH change represents a hundredfold increase in the concentration of H30+?
[A] pH 3 to pH 2
[B] pH 7 to pH 9
[C] pH 5 to pH 3
[D] pH 13 to pH 14
The
pH of a pond water is 9.0, after a spill of acid the pond is 1000 more acidic.
What is the new pH of the pond?
[A] 12
[B] 6
[C] 7
[D] 5
Which
of these pH numbers indicates the lowest level of acidity?
[A] 1
[B] 3
[C] 8
[D] 12
Which
pH indicates an acidic solution?
[A] 1
[B] 7
[C] 9
[D] 12
Which
of these 1 M solutions will have the highest pH?
[A] CH3OH
[B] HCl
[C] NaCl
[D] NaOH
The
relative level of acidity or alkalinity of a solution can be shown by using
their pH values.
True
False
On
the pH scale, each decrease of one unit of pH represents a tenfold increase in
[A] hydroxide concentration
[B] hydronium concentration
[C] both hydronium and hydroxide concentration