Tuesday, August 17, 2010

Acids, Bases and Buffers

Electrolyte is a substrate that conducts electricity when in solution, such as sodium chloride (NaCl). Many fluids contain strong electrolytes that break down or ionize into ions. Most acid and bases are electrolytes. An acid is a substrate that releases hydrogen ions (H+), when dissolved in water. Hydrogen atom without its electron is only a proton, an acid can be described as a proton donor. One molecule of Hydrogen chloride dissolves in water to produce hydrochloric acid which dissociates into one Hydrogen ion and one chlorine ion.
HCl ====> H+ + Cl-
In contrast, a base (or alkali) is a substrate that releases hydroxyl ions (OH-) when dissolved in water one molecule of sodium hydroxide dissolves in water to produce one sodium ion and one hydroxyl ion.
NaOH ====> Na+ + OH-
When a base dissolves in water it removes free protons (H+) from water and it is proton acceptor
OH- + H+ ====> H2O
pH: Measuring acidity and alkalinity:
Hydrogen and hydroxyl ions often affect the chemical reactions involved with life processes. Therefore the concentrations of these ions in body fluids are important. Higher the concentration of hydrogen ions (H+), more acidic the solution be.
If the concentration of hydroxyl (OH+) ions is higher in a solution, more basic or alkaline the solution is. A solution is neutral when the number of hydrogen ions equals the number of hydroxyl ions.
The pH scale runs from 0 to 14, measures acidity and alkalinity. Acidic solutions have pH less than 7 and basic (alkaline) solutions have pH above 7. A pH of 7 is neutral. Each whole number on pH scale represents a tenfold change (logarithmic) in acidity; therefore a solution with pH of 3 is 10 times more acidic than a solution with pH of 4 and pH of 9 is 10 times more basic than a pH of 8. Actually pH value is equal to negative logarithm of hydrogen ion concentration.
pH = –log [H+] or pH = Log (1/[H+])

pH: Control with Buffers:
Maintenance of stable internal environment in an animal requires constant pH of body fluids. A strong acid or base can destroy cell stability. Like wise sudden change in pH, may also be destructive. Fluid systems of most animals contain chemical substances that help, regulate the acid base balance. These substances called buffers resist changes in pH by accepting H+ ions when they are in excess and donating H+ ions when they are depleted. Most important buffers are bicarbonates, phosphates and organic molecules such as amino acids and proteins.

Carbonic acid – Bicarbonate ion System:
It is important in buffering the blood of many vertebrates. Carbonic acid dissociates to form Hydrogen ion and bicarbonate ion.
H2CO3 <====> H+ + HCO3-
In this example if H+ ions are added to the system, they combine with HCO3 to form H2CO3. This reaction removes H+ ions and keeps pH from changing.

Molecules of animals:
The chemicals that enter into or are produced by metabolic reactions can be divided into two large groups, organic molecules that contain carbon and inorganic molecules without carbon atoms. Most important characteristics of organic molecules depend on properties of key element carbon, the indispensable element for all life. Carbon atom has four electrons in the outermost shell, also requires four electrons to fill its outer orbits. Carbon atoms may share one or two pairs of electrons. When they share one pair of electron, single covalent bond is formed and still leaving carbon atoms to bond with other atoms. In case of ethane C2H6, two Carbons form covalent bond among themselves and the remaining three electrons share with three hydrogen atoms to form additional three single covalent bonds. In case of ethane C2H4, two covalent bonds are formed between two carbons and the remaining two electrons are shared with two hydrogen atoms.

H – C = C
Acetylene

     H     H
       |      |
H - C = C
Ethylene

     H     H
       |      |
H - C - C - H
       |      |
      H    H
Ethane

The ability of carbon to bond with other carbon atoms helps to develop carbon chains or rings of variable length and sizes. Bonds between Carbon and Hydrogen are also source of energy for living organisms Hydrocarbons are organic molecules that contain only carbon and hydrogen. Carbons are bended with each other in a linear fashion. Hydrocarbons form the frame work of all organic molecules.
Carbon chain or ring of many organic molecules provides relatively inactive molecular backbone to which reactive group or atoms are attached. These functional groups of molecules are responsible for molecules unique chemical properties and behaviour.

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