why does the ph scale range from 0 to 14

Introduction and Definitions: Acidic and basic are two extremes that describe a chemical
property chemicals. Mixing acids and bases can cancel out or
neutralize their extreme effects. A substance that is neither
acidic nor basic is neutral. The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH
less than 7 is acidic. A pH greater than 7 is basic. The pH scale is logarithmic and as a result, each whole pH
value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100
times (10 times 10) more acidic than pH 6. The same holds true
for pH values above 7, each of which is ten times more alkaline
(another way to say basic) than the next lower whole value.


For
example, pH 10 is ten times more alkaline than pH 9 and 100 times
(10 times 10) more alkaline than pH 8. Pure water is neutral. But when chemicals are mixed with water,
the mixture can become either acidic or basic. Examples of acidic
substances are vinegar and lemon juice. Lye, milk of magnesia,
and ammonia are examples of basic substances.
pH is a scale which quantities the concentration of hydrogen ion in a solution. The range of pH scale is between 0 to 14. The pH value increases with decrease in hydrogen ion concentration. If the value of pH is 0, this shows maximum hydrogen ion concentration. pH value equal to 14 shows lowest hydrogen ion concentration.


PH scale ranges from -infinity to infinity. It does not go below 0 and PH (0-14) corresponds to the 1 molar concentration of H+ and OH-В ions. for more concentrated solutions it will be out of scale and will not give accurate measurement. The pH of a solution is a measure of the molar concentration of hydrogen ions in the solution and as such is a measure of the acidity or basicity of the solution. The letters pH stand for "power of hydrogen" and numerical value for pH is just the negative of the power of 10 of the molar concentration of H ions. The usual range of pH values encountered is between 0 and 14, with 0 being the value for concentrated hydrochloric acid (1 M HCl), 7 the value for pure water (neutral pH), and 14 being the value for concentrated sodium hydroxide (1 M NaOH).


It is possible to get a pH of -1 with 10 M HCl, but that is about a practical limit of acidity. At the other extreme, a 10 M solution of NaOH would have a pH of 15. Numerical examples from Shipman, Wilson and Todd. In pure water, the molar concentration of H M. Actually, when looked at in detail, it is more accurate to classify the concentrations as those of [H. The product of the positive and negative ion concentrations is 10 in any aqueous solution at 25 C. An important example of pH is that of the blood. Its nominal value of pH = 7. 4 is regulated very accurately by the body. If the pH of the blood gets outside the range 7. 35 to 7. 45 the results can be serious and even fatal.


If you measure the pH of tap water with a pH meter, you may be surprised at how far from a pH of 7 it is because of dissolved substances in the water. Distilled water is necessary to get a pH near 7. Meters for pH measurement can give precise numerical values, but approximate values can be obtained with various indicators. Red and blue litmus paper has been one of the common indicators. Red litmus paper turns blue at a basic pH of about 5, and blue litmus paper turns red at an acid pH of about 8. Neither changes color if the pH is nearly neutral. Litmus is an organic compound derived from lichens. Phenolpthalein is also a common indicator, being colorless in solution at pH below 8 and turning pink for pH above 8.

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