Friday, November 26, 2010
pH , CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL
A chemical parcel man must understand the pH scale.
For example--- Zinc tanks can take cargoes only between pH 6 to 9 or zinc will shed and contaminate the cargo. Most epoxies cannot take pH less than 3.5, though the manufacturer will NEVER declare this.
The pH scale is from zero to 14.
Neutral fresh water pH is zero . In pure water which is neutral, the conc of Hydrogen ion is 10 raised to -7 equivalent/litre which corresponds to pH of 7.
Zero pH is an acid of highest strength like Hydrochloric acid . pH 14 is a base of highest strength like Caustic .
pH is a measure of hydrogen ion concentration in that solution. A small change in pH represents a large change in hydrogen ion concentration. As the conc of H+ ions increase by 10 times, the value of pH decreases by one unit and vice versa. This is because the pH scale is logarithmic. This means each change of one in pH value is 10 times more acidic.
So a substance with pH 2 is 1000 times more acidic than one with pH 5. In other words ( better to understand this well ) diluting a strong acid of pH 2 , ten times increase the pH value to pH 3.
Acidic soil is infertile, so lime is added. Thiobacillus ferro oxidans ( bacteria ) lowers pH to 2 or even 0.7. Some lakes are fairly acidic ( pH 3.7 to 5.5 ). Be aware when a charterer while trying to save some money for TCFW tells you to dilute say molasses cargo with lake intake. Boiler feed water water cannot be acidic so additives are added to keep it basic.
Neutral or pure water has an equal conc of H+ ions and OH- ions. When an acid is added the conc of H+ ions become greater than that of OH- ions. Similarly when a base is added the conc of OH- ions increases while that of H+ decreases.
Thus an acid solution is one in which H+ is greater than 10 raised to -7.
pH changes with temp. It decreases on heating. pH of boiling water is 6.56.
The pH of DI water drops from 7 to 5.5 due to some reaction in water when splashed in air. Rain ph is 5.6 as CO2 dissolves to form carbonic acid. This is the reason why the DI water spray turns slightly acidic
Few pH values:---
Hydrochloric acid/ 0
Gastric stomach juice/ 1
Coca cola/ 2.5
Orange juice /3.0
Fresh water/ 7
Sea water/ 8
Tooth paste/ 9.9
Prior loading certain cargoes the pH value of the tank internals and attachments are taken to make sure they are neutral ( Phenol ).
Canned food is sterilized by lowering pH using acidulants like citric, acetic, fumaric, ascorbic, propionic, lactic, adipic, tartaric etc.
pH in water at room temp 25C-- there is only one hydrogen ion for every 555 million water molecules. Basically ph scale measures the amount of H+ and OH-.
A person cannot survive if his blood ph drops to 7 or rises to 7.8. The buffering capacity of blood prevents such swings in pH level.
The gentleman who invented pH wanted to know how acidic his beer was. Beer needs yeast and yeast uses enzymes. Enzymes work only if pH is right. Beer is pH3
For the erudite— The pH of a solution depends on the concentration of ionized protons and not the total concentration of acid. If there is an excess of protons it is an acidic solution. If there is a shortage of protons it is basic.
Bufferclean 5.5 removes all zinc white salts and brings it down like snow fall.
Buffer solution resists any change of its pH value due to dilution or an addition of solution of acid/ alkali. The process by which H+ or OH- ions are removed so that pH remains constant is known as buffer action.
CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )