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Weak acid ionization constants, k
HNO 2 5∙10 -4 3.3
HCN 4.9∙10 -10 9.3
HIO 2.3∙10 -11 10.6
HF 3.5∙10 -4 3.4
HOCN 3.5∙10 -4 3.4
HClO 2 1.1∙10 -2 2.0
CH 3 COOH (acetic acid) 1.7∙10 -5 4.8
CH3CH 2 COOH (propionic acid) 1.4∙10 -5 4.9

We make two final notes about the results in Table 5. First, it is clear the larger the value of K a , the stronger the acid. That is, when K a is a larger number, the percent ionization of the acid is larger, and vice versa. Second, the values of K a vary over many orders of magnitude. As such, it is often convenient to define the quanity pK a , analogous to pH, for purposes of comparing acid strengths:

pK a = -log 10 K a

The value of pK a for each acid is also listed in Table 5. Note that a small value of pK a implies a large value of K a and thus a stronger acid. Weaker acids have larger values of pK a . K a and pK a thus give a simple quantitative comparison of the strength of weak acids.

Observation 3: autoionization of water

Since we have the ability to measure pH for acid solutions, we can measure pH for pure water as well. It might seem that this would make no sense, as we would expect [H 3 O + ] to equal zero exactly in pure water. Surprisingly, this is incorrect: a measurement on pure water at 25 ºC yields pH = 7, so that [H 3 O + ] = 1.0·10 -7 M. There can be only one possible source for these ions: water molecules. The process

H 2 O(l) + H 2 O(l) → H 3 O + (aq) + OH - (aq)

is referred to as the "autoionization" of water. Note that, in this reaction, some water molecules behave as acid, donating protons, while other acid molecules behave as base, accepting protons.

Since at equilibrium [H 3 O + ] = 1.0·10 -7 M, it must also be true that [OH - ] = 1.0·10 -7 M. We can write the equilibrium constant for Reaction (6), following our previous convention of omitting the pure water from the expression, and we find that, at 25 ºC,

K w = [H 3 O + ][OH - ] = 1.0·10 -14

(In this case, the subscript "w" refers to "water.")

Reaction (6) occurs in pure water but must also occur when ions are dissolved in aqueous solutions. This includes the presence of acids ionized in solution. For example, we consider a solution of 0.1 M acetic acid. Measurements show that in this solution, [H 3 O + ] = 1.3·10 -3 M and [OH - ] = 7.7·10 -12 M. We note two things from this observation: first, the value of [OH - ] is considerably less than in pure water; second, the autoionization equilibrium constant remains the same at 1.0·10 -14 . From these notes, we can conclude that the autoionization equilibrium of water occurs in acid solution, but the extent of autoionization is suppressed by the presence of the acid in solution.

We consider a final note on the autoionization of water. The pH of pure water is 7 at 25 ºC. Adding any acid to pure water, no matter how weak the acid, must increase [H 3 O + ], thus producing a pH below 7. As such, we can conclude that, for all acid solutions at 25 ºC, their pH is less than 7, or in other words, any solution with pH less than 7 is acidic.

Observation 4: base ionization, neutralization and hydrolysis of salts

We have not yet examined the behavior of base molecules in solution, nor have we compared the relative strengths of bases. We have defined a base molecule as one which accepts a positive hydrogen ion from another molecule. One of the most common examples is ammonia, NH 3 . When ammonia is dissolved in aqueous solution, the following reaction occurs:

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
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