PH. In any solution the H 3 O + and OH - concentration is always very small. pH- method of representing the H 3 O + concentration in a solution. pH =

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Presentation transcript:

pH

In any solution the H 3 O + and OH - concentration is always very small. pH- method of representing the H 3 O + concentration in a solution. pH = -log [H 3 O + ] So the pH of water is… pH = - log 1 x10 -7 pH = 7

What is a log log stands for logarithm ~we can use them to solve for an exponent. log x y = y log x For example log 1 x10 -7 = -7 the log key on your calculator is log 10 meaning it will cancel out a 10^. To reverse a log 10 raise the whole thing to the 10 th power (10 ^ ), this is an antilog The reversed pH equation is [H 3 O + ] = 10^(-pH)

pH values pH of 7 is neutral- equal [H 3 O + ] and [OH - ] below 7 is acidic, higher [H 3 O + ] than [OH - ] above 7 is basic or alkaline, higher [OH - ] than [H 3 O + ]

Acid Base Equations [H 3 O + ] [OH - ] = 1 x pH = -log [H 3 O + ] [H 3 O + ] = 10^(-pH)

Sig Figs and pH The number of decimal places in the log value, pH value, is equal to the number of significant figures in the number that we took the logarithm of, concentration. So [H 3 O + ] = 2.45 x10 -4 M 3 sig figs pH = -log 2.45 x10 -4 M = decimal places

Reversing that Having a pH of 4.32 (2 decimal places) gives you a hydronium concentration of… [H 3 O + ] = 10^(-4.32) = 4.8 x10 -5 M (2 sig figs)

pH problems What is the pH of a 2.4 x M H 3 O + ? pH = - log 2.4 x pH = 3.62 What is the OH - concentration? [H 3 O + ] [OH - ] = 1 x x10 -4 [OH - ] = 1 x [OH - ] = 4.2 x M

Backwards problem What is the [H 3 O + ] and [OH - ] of a solution with a pH of 8.75? [H 3 O + ] = 10^(-pH) [H 3 O + ] = [H 3 O + ] = 1.8 x M 1.78…x10 -9 [OH - ] = 1 x [OH - ] = 5.6 x M

Last one What is the pH and [H 3 O + ] of a solution with a [OH - ] conc. of 2.9 x10 -4 M? [H 3 O + ] 2.9 x = 1 x [H 3 O + ] = 3.4 x M (2 sig figs) pH = -log x pH = (2 decimal places)

Homework What is the pH and [H 3 O + ] of a solution with a [OH - ] of 5.92 x10 -5 M?