<< Chapter < Page Chapter >> Page >

We consider a final note on the autoionization of water. The pH of pure water is 7 at 25°C. Adding any acidto 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, pH is less than 7, or on the other hand, anysolution 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 strengthsof bases. We have defined a base molecule as one which accepts a positive hydrogen ion from another molecule. One of the most commonexamples is ammonia, NH 3 . When ammonia is dissolved in aqueous solution, the followingreaction occurs:

N H 3 ( aq ) + H 2 O ( l ) N H 4 + ( aq ) + O H - ( aq )

Due to the lone pair of electrons on the highly electronegative N atom,NH 3 molecules will readily attach a free hydrogen ion forming theammonium ion NH 4 + . When we measure the concentration ofOH for various initial concentration of NH 3 in water, we observe the results in [link] . We should anticipate that a base ionization equilibrium constant might exist comparable to the acidionization equilibrium constant, and in [link] , we have also calculated the value of the function K b defined as:

K b [ N H 4 + ] [ O H - ] [ N H 3 ]
Equilibrium concentrations and kb for ammonia
C 0 (M) [OH ] K b pH
0.50 3.2 × 10 –3 2.0 × 10 –5 11.5
0.20 2.0 × 10 –3 2.0 × 10 –5 11.3
0.10 1.4 × 10 –3 2.0 × 10 –5 11.1
0.050 9.7 × 10 –4 1.9 × 10 –5 11.0
0.020 6.0 × 10 –4 1.9 × 10 –5 10.8
0.010 4.2 × 10 –4 1.9 × 10 –5 10.6
0.005 3.0 × 10 –4 1.9 × 10 –5 10.5
0.001 1.3 × 10 –4 1.8 × 10 –5 > 10.1
0.0005 8.7 × 10 –5 1.8 × 10 –5 9.9

Given that we have dissolved a base in pure water, we might be surprised to discover the presence of positivehydrogen ions, H 3 O + , in solution, but a measurement of the pH for each of the solutionsreveals small amounts. The pH for each solution is also listed in [link] . The source of these H 3 O + ions must be the autoionization of water. Note, however, that in each case in basic solution, the concentration ofH 3 O + ions is less than that in pure water. Hence, the presence of the base in solution has suppressed the autoionization. Because ofthis, in each case the pH of a basic solution is greater than 7.

Base ionization is therefore quite analogous to acid ionization observed earlier. We now consider a comparisonof the strength of an acid to the strength of a base. To do so, we consider a class of reactions called "neutralizationreactions" which occur when we mix an acid solution with a base solution. Since the acid donates protons and the base acceptsprotons, we might expect, when mixing acid and base, to achieve a solution which is no longer acidic or basic. For example, if we mixtogether equal volumes of 0.1M HCl(aq)and 0.1M NaOH(aq),the following reaction occurs:

H Cl ( aq ) + Na O H ( aq ) Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )

The resultant solution is simply a salt solution withNaCl dissolved in water. This solution has neither acidic nor basicproperties, and the pH is 7; hence the acid and base have neutralized each other. In this case, we have mixed together astrong acid with a strong base. Since both are strong and since we mixed equal molar quantities of each, the neutralization reactionis essentially complete.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Berger describes sociologists as concerned with
Mueller Reply
what is hormones?
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Chemistry of life: bis2a modules 2.0 to 2.3 (including appendix i and ii). OpenStax CNX. Jun 15, 2015 Download for free at https://legacy.cnx.org/content/col11826/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry of life: bis2a modules 2.0 to 2.3 (including appendix i and ii)' conversation and receive update notifications?