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Understanding pH Calculations and Equations for Acid-Base Chemistry

This lesson provides a comprehensive overview of pH calculations essential for understanding acid-base chemistry. Key equations related to water ionization at 25°C are included, such as Kw=[H+][OH-]=1.00×10^-14 and calculations for pH and pOH. Detailed examples illustrate how to compute pH from hydrogen ion concentrations and calculate pOH using hydroxide ion concentrations. The lesson also emphasizes significant figures in calculations and the distinction between acidic and basic solutions based on pH values.

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Understanding pH Calculations and Equations for Acid-Base Chemistry

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  1. Acids Lesson 10 pH Calculations

  2. pH Equations You must know the following equations, which are all based on the ionization of water at 250 C! H2O ⇄ H+ + OH- Kw = [H+][ OH-] = 1.00 x 10-14 pH= -Log[H+]pOH= -Log[OH-] [H+]= 10-pH [OH-]= 10-pOH pH + pOH = pKw = 14.000

  3. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M Calculation

  4. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M Calculation The number of sig figs are 2 (green)

  5. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M Calculation pH = -Log[H+] pH = -Log[2.5 x 10-4] pH = 3.60The digit before the decimal does not count as a sig fig. Both digits after the decimal count for 2 sig figs.

  6. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 3.60 Calculation pH = -Log[H+] pH = -Log[2.5 x 10-4] pH = 3.60keep all digits on the calculator- do not round!

  7. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 3.60 Calculation pH + pOH = 14.00 3.60 + pOH = 14.00 pOH = 10.40

  8. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 3.60 10.40 Calculation [OH-] = 10-pOH [OH-] = 10-10.40 [OH-] = 4.0 x 10-11 M

  9. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 Calculation Note that all of the entries in the last line have two sig figs!

  10. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 9.435 Calculation pH + pOH = 14.000 9.435 + pOH = 14.000 pOH = 4.565

  11. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 9.435 4.565 Calculation [OH-] = 10-pOH [OH-] = 10-4.565 [OH-] = 2.72 x 10-5 M

  12. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 2.72 x 10-5 M9.435 4.565 Calculation [H+][OH-] = 1.00 x 10-14 [H+][2.72 x 10-5 ] = 1.00 x 10-14 [H+] = 3.67 x 10-10 M

  13. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 Calculation Note that all of the entries in the last line have three sig figs!

  14. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 2.6 x 10-4 M Calculation pOH = -Log[OH-] pOH = -Log[2.6 x 10-4] pOH = 3.59

  15. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 2.6 x 10-4 M3.59 Calculation pH + pOH = 14.000 pH +3.59 = 14.000 pOH = 10.41

  16. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 2.6 x 10-4 M10.413.59 Calculation [H+] = 10-pH [H+] = 10-10.41 [H+] = 3.8 x 10-11 M

  17. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 Calculation Note that all of the entries in the last line have two sig figs!

  18. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 8.40

  19. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 4.0 x 10-9 M8.40

  20. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 4.0 x 10-9 M8.40

  21. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 2.5 x 10-6 M4.0 x 10-9 M8.40

  22. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 2.5 x 10-6 M4.0 x 10-9 M5.608.40

  23. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 2.5 x 10-6 M4.0 x 10-9 M5.608.40 Calculation Note that all of the entries in the last line have two sig figs!

  24. pH Calculations [H+] [OH-] pH pOH 2.5 x 10-4 M 4.0 x 10-11 M 3.60 10.40 acid 3.67 x 10-10 M2.72 x 10-5 M9.435 4.565basic 3.8 x 10-11 M 2.6 x 10-4 M10.413.59 basic 2.5 x 10-6 M4.0 x 10-9 M5.608.40 acid If the pH is lower than 7, the solution is acidic! If the pH is greater than 7, the solution is basic!

  25. 1. Calculate the pH of 0.40 M HI. HI H+ + I- 0.40 M 0.40 M 0.40 M pH = -Log[H+] pH = -Log[0.40] pH = 0.40

  26. 2. Calculate the pH of 0.030 M Ba(OH)2. Ba(OH)2 Ba2+ + 2OH- 0.030 M 0.030 M 0.060 M pOH = -Log[OH-] pOH = -Log[0.060] pOH = 1.22 pH + pOH = 14.000 pH +1.22 = 14.000 pH = 12.78

  27. 3. Calculate the pH of 100.0 mL of 1.0 M HCl after 300.0 mL of water is added to it. HCl H+ + Cl- 1001.0M 400 0.25M0.25M pH = 0.60

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