what is meaning of the buffer solution?

Question

when we are use the I.R Spectroscopy

Answer 1

Buffer solutions are solutions which resist change in hydronium ion and the hydroxide ion concentration (and consequent pH) upon addition of small amounts of acid or base, or upon dilution. Buffer solutions consist of a weak acid and its conjugate base (more common) or a weak base and its conjugate acid (less common). The resistive action is the result of the equilibrium between the weak acid (HA) and its conjugate base (A-):

Answer 2

Buffer solutions are solutions which resist change in hydronium ion and the hydroxide ion concentration (and consequently resists changes to the pH) upon addition of small amounts of acid or base, or upon dilution.

Buffer solutions most commonly consist of a weak acid, though a buffer solution made from a weak alkaine is also possible.

Answer 3

A buffer solution stabilizes the pH of a solution.

Answer 4

buffers resist small changes in ph value when an acid or base is added or even when diluted

Answer 5

buffer solution is that solution whose PH does not change by adding acidic or basic solution.

Answer 6

buffer suppresses the action of acid or the base present in the soln. by acting as complimentary acid or base

Answer 7

Definition

A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it.

Acidic buffer solutions

An acidic buffer solution is simply one which has a pH less than 7. Acidic buffer solutions are commonly made from a weak acid and one of its salts - often a sodium salt.

A common example would be a mixture of ethanoic acid and sodium ethanoate in solution. In this case, if the solution contained equal molar concentrations of both the acid and the salt, it would have a pH of 4.76. It wouldn't matter what the concentrations were, as long as they were the same.


You can change the pH of the buffer solution by changing the ratio of acid to salt, or by choosing a different acid and one of its salts.

Note: If you need to know about calculations involving buffer solutions, you may be interest in my chemistry calculations book.


Alkaline buffer solutions

An alkaline buffer solution has a pH greater than 7. Alkaline buffer solutions are commonly made from a weak base and one of its salts.

A frequently used example is a mixture of ammonia solution and ammonium chloride solution. If these were mixed in equal molar proportions, the solution would have a pH of 9.25. Again, it doesn't matter what concentrations you choose as long as they are the same.


How do buffer solutions work?

A buffer solution has to contain things which will remove any hydrogen ions or hydroxide ions that you might add to it - otherwise the pH will change. Acidic and alkaline buffer solutions achieve this in different ways.

Acidic buffer solutions

We'll take a mixture of ethanoic acid and sodium ethanoate as typical.

Ethanoic acid is a weak acid, and the position of this equilibrium will be well to the left:



Adding sodium ethanoate to this adds lots of extra ethanoate ions. According to Le Chatelier's Principle, that will tip the position of the equilibrium even further to the left.

Note: If you don't understand Le Chatelier's Principle, follow this link before you go any further, and make sure that you understand about the effect of changes of concentration on the position of equilibrium.

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The solution will therefore contain these important things:

lots of un-ionised ethanoic acid;

lots of ethanoate ions from the sodium ethanoate;

enough hydrogen ions to make the solution acidic.

Other things (like water and sodium ions) which are present aren't important to the argument.

Adding an acid to this buffer solution

The buffer solution must remove most of the new hydrogen ions otherwise the pH would drop markedly.

Hydrogen ions combine with the ethanoate ions to make ethanoic acid. Although the reaction is reversible, since the ethanoic acid is a weak acid, most of the new hydrogen ions are removed in this way.



Since most of the new hydrogen ions are removed, the pH won't change very much - but because of the equilibria involved, it will fall a little bit.

Adding an alkali to this buffer solution

Alkaline solutions contain hydroxide ions and the buffer solution removes most of these.

This time the situation is a bit more complicated because there are two processes which can remove hydroxide ions.

Removal by reacting with ethanoic acid

The most likely acidic substance which a hydroxide ion is going to collide with is an ethanoic acid molecule. They will react to form ethanoate ions and water.



Note: You might be surprised to find this written as a slightly reversible reaction. Because ethanoic acid is a weak acid, its conjugate base (the ethanoate ion) is fairly good at picking up hydrogen ions again to re-form the acid. It can get these from the water molecules. You may well find this reaction written as one-way, but to be fussy about it, it is actually reversible!


Because most of the new hydroxide ions are removed, the pH doesn't increase very much.

Removal of the hydroxide ions by reacting with hydrogen ions

Remember that there are some hydrogen ions present from the ionisation of the ethanoic acid.



Hydroxide ions can combine with these to make water. As soon as this happens, the equilibrium tips to replace them. This keeps on happening until most of the hydroxide ions are removed.



Again, because you have equilibria involved, not all of the hydroxide ions are removed - just most of them. The water formed re-ionises to a very small extent to give a few hydrogen ions and hydroxide ions.


Alkaline buffer solutions

We'll take a mixture of ammonia and ammonium chloride solutions as typical.

Ammonia is a weak base, and the position of this equilibrium will be well to the left:



Adding ammonium chloride to this adds lots of extra ammonium ions. According to Le Chatelier's Principle, that will tip the position of the equilibrium even further to the left.

The solution will therefore contain these important things:

lots of unreacted ammonia;

lots of ammonium ions from the ammonium chloride;

enough hydroxide ions to make the solution alkaline.

Other things (like water and chloride ions) which are present aren't important to the argument.

Adding an acid to this buffer solution

There are two processes which can remove the hydrogen ions that you are adding.

Removal by reacting with ammonia

The most likely basic substance which a hydrogen ion is going to collide with is an ammonia molecule. They will react to form ammonium ions.



Most, but not all, of the hydrogen ions will be removed. The ammonium ion is weakly acidic, and so some of the hydrogen ions will be released again.

Removal of the hydrogen ions by reacting with hydroxide ions

Remember that there are some hydroxide ions present from the reaction between the ammonia and the water.



Hydrogen ions can combine with these hydroxide ions to make water. As soon as this happens, the equilibrium tips to replace the hydroxide ions. This keeps on happening until most of the hydrogen ions are removed.



Again, because you have equilibria involved, not all of the hydrogen ions are removed - just most of them.

Adding an alkali to this buffer solution

The hydroxide ions from the alkali are removed by a simple reaction with ammonium ions.



Because the ammonia formed is a weak base, it can react with the water - and so the reaction is slightly reversible. That means that, again, most (but not all) of the the hydroxide ions are removed from the solution.
Full details refer to:
http://www.chemguide.co.uk/physical/acidbaseeqia/buffers.html

Spectroscopy is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from them or absorbed in them. A device for recording a spectrum is a spectrometer. Spectroscopy can be classified according to the physical quantity which is measured or calculated or the measurement process.

SPTRY used for
Spectroscopy is also heavily used in astronomy and remote sensing. Most large telescopes have spectrographs, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of spectral lines.

Also
IR spectroscopy has been used to study distant galaxies, weather-resistant finishes for cars, and pollutants in the atmosphere. Farmers can locate soggy spots in their fields using the IR signal from water, and food processing companies can identify rotten fruit or bug-infested breakfast cereals as they go by on the conveyor belt. In the crime lab, IR helps to identify illegal drugs and trace the sources of tiny pieces of evidence from a crime scene.

The instrument used for this analysis is called an IR spectrophotometer, and most of the instruments used today are variations on the same basic design. The light source, which can be a heated ceramic-coated wire or a tungsten or mercury lamp, emits light in all directions over a wide range of wavelengths in the visible and IR regions.
For IR spectroscopy refer to
http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm