Kates Playground Hardcpre

pH of acidic and basic solutions

At this stage of development of our course, we all know that the acidity of the acids is due to the positive hydrogen ions or protons and the basicity or alkalinity of hydroxides is due to hydroxide ions. In this section, we will learn to express the acidity or alkalinity of the solutions or different ways, in terms of the proton concentration that exists in them, but to achieve this end we must, above, to clarify our ideas about acids and bases.

THEORIES ACIDS AND BASES .- Among them are the following two.

Arrhenius theory .- states that an acid is any substance in solution is capable of yielding positive hydrogen ions or protons (H +) and bases is any substance in solution water is able to give hydroxide ions (OH-), as suggested in the following examples:

Brønsted-Lowry Theory .- It states:

a) ACID .- Any molecule or ion capable yield positive hydrogen ions or protons (H +) in aqueous solution.

now know that protons that protons can not exist in free state, but rarely are immediately combined with a water molecule forming a hydronium ion.

From the above it follows that the hydronium ion is the predominant ionic species in acidic solutions, but for reasons practical is often said that in an acidic environment dominated by positive hydrogen ions or protons

b) BASE .- Any molecule or ion capable of accepting positive hydrogen ions or protons.

From observation of the last equation we can deduce that the substances in the hydroxide ion present structure are fundamental in nature.

ELECTROLYTES AND WEAKNESSES .- Recall that all acids, hydroxides and salts, when dissolved in water partially or completely dissociate into ions, which is why they are called electrolytes.

An electrolyte that dissociates wholly or almost wholly on strong electrolyte ions are called, but few molecules dissociate into ions below 5%, are called weak electrolytes.

strong electrolytes are: HCl, HBr, HI, HNO3, HClO4, H2SO4, NaCl, LiOH, NaOH, RbOH, CsOH, Mg (OH) 2, Ca (OH) 2, Sr (OH) 2, Ba (OH) 2, etc.

are weak electrolytes: H2S, H3PO4, HF, H3BO3, H2SO3, HNO2, H2CO3, HClO, HCN, NH3, etc..

acids and bases that have a high degree of ionization are strong acids or bases, while those with low degree of ionization are weak acids or bases.

Ionic product of water (kW) .- It has been shown experimentally that very little water is ionized, as suggested below:

liter of water in a 10-7 moles dissociate water and there therefore 10-7 moles of protons and 10-7 moles of hydroxide ions.

The ionic product of water (Kw) is a constant that results from theoretically multiply the proton concentration [H +] and hydroxide ion concentration [OH-] that exist in a liter of water.

acid solution, basic and neutral .- If we add acid to water, increase the concentration protons, H +, above 10-7 mol / L, but as the ionic product of water is a constant and should remain as such, the concentration of hydroxide ions, OH-, must decrease.

It follows that a solution is acidic if the concentration of protons is greater than 10-7 mol / L.

Given the above reasoning, we must conclude the following:

CONCEPT .- pH pH is a way of expressing the acidity or basicity (alkalinity) of a medium, using simple whole numbers 1 to 14.

These are calculated valortes the negative logarithm of the concentration of positive hydrogen ions or protons that success in a particular environment.

In correspondence with the above, the pH is defined as the negative logarithm of the concentration of protons that exist in a medium or as the decimal logarithm of the reciprocal of the concentration of protons.

IMPORTANCE OF pH .- From a biological standpoint, the pH is very important because living organisms must remain more or less constant due to the existence of adequate regulatory mechanisms. Any significant variation of it is incompatible with life. The pH of blood is approximately 7.

The land usually has a pH of between 5 and 7. We must stress that each plant species requires a specific pH for normal development, hence the great importance of studying the pH of soils in agricultural activities.

or buffer BUFFER SOLUTIONS .- Mixtures of weak acids and their salts, or mixture of weak bases and their salts, are called buffer solutions or buffer because they resist changes in hydrogen ion concentration positive or protons (H +) produced by the addition of small amounts of acids or bases.

The following are some cushions important

Blood is an important example of buffer in which the acid and the ion damping action exerted are carbonic acid, H2CO3, and bicarbonate or hydrogen carbonate ion, HCO3-. When you receive a hydrogen ion excess blood, eliminated almost entirely by the reaction:

And when there is an excess of hydroxide ion, it is absorbed by the reaction:

By this mechanism, the pH human blood is kept close to 7.35, ie slightly alkaline. If blood pH is less than 7.35 the condition is called acidosis, and if it rises above of 7.45 will have a condition called alkalosis. If the elevation is above 7.8 or below 6.8 (due to a defective breathing, starvation, renal failure or some other disease) the person can suffer irreversible brain damage or even death.