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In any solution the H 3 O + and OH - concentration is always very small.

pH. 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

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In any solution the H 3 O + and OH - concentration is always very small.

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  1. pH

  2. 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

  3. What is a log • log stands for logarithm • ~we can use them to solve for an exponent. • log xy = y log x • For example log 1 x10-7 = • -7 • the log key on your calculator is log10 meaning it will cancel out a 10^. • To reverse a log10 raise the whole thing to the 10th power (10^), this is an antilog • The reversed pH equation is • [H3O+] = 10^(-pH)

  4. pH values • pH of 7 is neutral- equal [H3O+] and [OH-] • below 7 is acidic, higher [H3O+] than [OH-] • above 7 is basic or alkaline, higher [OH-] than [H3O+]

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

  6. Sig Figs and pH • The number of decimal places in the log value, pH value, is equal to the number of significant figuresin 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

  7. 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)

  8. 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

  9. Backwards problem • What is the [H3O+] and [OH-] of a solution with a pH of 8.75? • [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

  10. Last one • What is the pH 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)

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

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