pH scales

pH definition

• pH is a measure the concentration of hydrogen ions.​

• pH measures the acidity or basicity (alkalinity) of a substance.

pH scale

pH scale: 0-14​

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pH < 7 : acid​

pH of 7: neutral​

pH > 7 : base (alkaline) 

pH equation

pH is the “negative logarithm of” the hydrogen ion concentration​

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pH = -log[H+]​

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This means if the pH changes by 1, there’s 10 times difference in the concentration​

If the pH changes by 2, there’s a 100 times difference in the concentration​

If the pH changes by 3, there’s a 1000 times difference in the concentration

log rules

Equation to calculate pH​

pH = -log[H+]​

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Equation to calculate concentration of H+ ions​

10-pH = [H+]

concentration will be in molL/if it is the square brackets, which means it is also in molL.

pOH

• a measure of hydroxide ion (OH-) concentration. ​

• measure of the alkalinity of a solution​

• pOH less than 7 are alkaline, pOH greater than 7 are acidic and pOH equal to 7 are neutral. O PPOSITE to pH! There are several ways to define acids and bases, but pH and pOH refer to hydrogen ion concentration and hydroxide ion concentration, respectively. ​

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what does the “p” stand for?

"negative logarithm of" and is used to make it easier to work with extremely large or small values. pH and pOH are only meaningful when applied to aqueous (water-based) solutions.​

relating pOH and pH

Calculate the pH of a 0.2 mol L–1 solution of sodium hydroxide.

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