PH.

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PH worksheet (#1).

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Presentation transcript:

pH

pH In any solution the H3O+ and OH- concentration is always very small. pH- method of representing the H3O+ concentration in a solution. pH = -log [H3O+] So the pH of water is… pH = - log 1 x10-7 pH = 7 Anything with a pH below 7 is acidic, above 7 is basic.

pOH pOH- very similarly to pH, this is a method of representing the OH- concentration in a solution. pH = - log [OH-] So the pH of water is… pH = - log 1 x10-7 pH = 7 This is the reverse of pH. Below 7 is basic, above 7 is acidic.

Acid Base Equations pH = -log [H3O+] [H3O+] = 10^(-pH) pOH = -log [OH-] [OH-] = 10^(-pOH) pH + pOH = 14 [H3O+] [OH-] = 1 x 10-14

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 [H3O+] = 2.45 x10-4 M 3 sig figs pH = -log 2.45 x10-4 M = 3.611 3 decimal places

Reversing that Having a pH of 4.32 (2 decimal places) gives you a hydronium concentration of… [H3O+] = 10^(-4.32) = 4.8 x10-5 M (2 sig figs)

pH problems What is the pH of a 2.4 x 10-4 M H3O+? pH = - log 2.4 x 10-4 pH = 3.62 What is the OH- concentration? [H3O+] [OH-] = 1 x 10-14 2.4 x10-4 [OH-] = 1 x 10-14 [OH-] = 4.2 x10-11 M What is the pOH pOH = -log 4.2x10-11 M or pOH = 14-3.62 pOH = 10.38

Backwards problem What is the pOH, [H3O+] and [OH-] of a solution with a pH of 8.75? pOH = 14- 8.75 pOH = 5.25 [H3O+] = 10^(-pH) [H3O+] = 10-8.75 [H3O+] = 1.8 x 10-9 M 1.78…x10-9 [OH-] = 1 x 10-14 [OH-] = 5.6 x 10-6 M

Last one What is the pH, pOH and [H3O+] of a solution with a [OH-] conc. of 2.9 x10-4 M? [H3O+] 2.9 x 10-4 = 1 x 10-14 [H3O+] = 3.4 x 10-11 M (2 sig figs) pH = -log 3.448275 x 10-11 pH = 10.46 (2 decimal places) pOH =14 -10.46 pOH = 3.54 (2 decimal places)

Homework What is the pH, pOH, and [H3O+] of a solution with a [OH-] of 5.92 x10-5 M?