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Calculating pH

Calculating pH. Students will calculate the pH of strong acid and base solutions. Show How Water Becomes an Acid and an Base at the Same Time. Explain How Water Becomes An Acid and a Base. Using an Equation H 2 O  H + + OH -. What does it mean if an ion is put in brackets?.

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Calculating pH

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  1. Calculating pH Students will calculate the pH of strong acid and base solutions.

  2. Show How Water Becomes an Acid and an Base at the Same Time

  3. Explain How Water Becomes An Acid and a Base • Using an EquationH2O  H+ + OH-

  4. What does it mean if an ion is put in brackets? • [H+] means the concentration of the hydrogen ion in moles/liter. (M) • [OH-] means the concentration of the hydroxide ion in moles/liter. (M)

  5. ANOTHER CONSTANT! • In all solutions made with water as the solvent ………………… ta dut ta da!

  6. Why Does [H+] = [OH-] in Pure Water? • For each H+ ion formed a OH- ion also forms. So they have to be equal

  7. Values of [H+] and [OH-] in pure water • [H+] = 0.000 000 100 • Or [H+] = 1.0 x 10-7 • [OH-] = 0.000 000 100 • Or [OH-] = 1.0 x 10-7 • What happens to the [H+] when acid is added? • What happens to the [OH-] when acid is added?

  8. Instant Question 1. What happens to the [OH-] when acid is added? A. It goes up B. It goes down C. No change

  9. Instant Question 2. What happens when a water molecule breaks apart in a sample of water? a. It breaks into an H+ ion and a OH- ion. b. It breaks into two acid molecules c. It breaks into 2 H+ ions d. It breaks into 2 OH- ions.

  10. Instant Question 3. How does the [OH-] compare to the [H+] in pure water? a. the [H+] is greater b. the [OH-] is greater c. they equal one another

  11. 10.0 grams of HCl is dissolved in enough water to make 300 ml of solution • How is [H+] calculated? [H+] = molarity of the acid. • Find M of the acid and [H+] is that value.

  12. How is [OH-] calculated? • Just calculate the molarity of the base. • If the base has more than one OH- like Ba(OH)2 for example, then double the molarity. • Calculate the [OH-] if 15.0 grams of NaOH is dissolved in enough water to make 500 ml.

  13. Instant Question 4. Calculate the [OH-] if 25.0 grams of KOH is dissolved in enough water to make 3500 ml Report 3 decimal places for example 0.326

  14. What is pH? • pH is the negative log of the [H+] • pH = -Log [H+] • Why is the pH of water 7? • Recall: [H+] = 0.000 000 100 • Log 0.000 000 100 = -7 • -Log = 7

  15. Find the -log of these numbers • 0.001 ______________ • 0.000001 ___________ • 0.1 ______________ • 1 ______________ • 10 ______________ • 0.000000001 _________

  16. Define pOH • pOH is the –log of the [OH-] • How are pH and pOH related? • pH + pOH = 14

  17. Instant Questions! 5. Find the [H+], if pH = 5 Write the answer in this form 0.001 6. Find the [OH-] if pH = 9

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