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Formulate an operational definition of pH Solve problems involving pH

Formulate an operational definition of pH Solve problems involving pH Describe how an acid-base indicator works in terms of colour shifts and Le Chatelier’s Principle. Additional KEY Terms. Acidic: [H 3 O + ] > [OH - ] Alkaline (basic): [OH - ] > [H 3 O + ]

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Formulate an operational definition of pH Solve problems involving pH

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  1. Formulate an operational definition of pH • Solve problems involving pH • Describe how an acid-base indicator works in terms of colour shifts and Le Chatelier’s Principle Additional KEY Terms

  2. Acidic: [H3O+] > [OH-] Alkaline (basic): [OH-] > [H3O+] Neutral: [OH-] = [H3O+] 1909 - Soren Sorensen developed a simplified system for the degree of acidity of a solution. pH - the potenz (power) of hydrogen - German potentia hydrogenii - Latin

  3. Convenient and simple way to express [H+] • Equation 1: pH = - log [H+] • Equation 2: [H3O+] = 10-pH pOH has its own scale – like pH – that runs from 0-14 for strength of bases. Equation 3:pOH = - log [OH-] Equation 4: [OH-] = 10-pOH

  4. In a neutral solution pH & pOH = 7 Acidic - pH < 7 Basic - pH > 7 Equation 5:pH+pOH = 14

  5. Calculate the pH of an HCl solution whose concentration is 5.0 x 10-6 mol/L. remember strong acids are 100% dissociating: [HA]i = [H+]e = [A-]e pH = -log[H+] = -log(5.0 x 10-6 M) = -(-5.30) = 5.30

  6. The pH of a solution is 3.25. Calculate the hydrogen ion concentration in the solution. [H3O+] = 10-pH Find the “10 x” button on your calculator. = 10-3.25 = 5.6 x 10-4 M

  7. The pH of a solution is 10.30, what is the hydroxide ion concentration? OR solved this way pOH = 14.00 - pH pOH = 14.00 - 10.30 = 3.70 [H+] = 10-pH [OH-] = KW [H+] [OH-] = 10-pOH = 10-3.70 = 2.0 x 10-4 mol/L

  8. Mg(OH)2 (s) Mg2+(aq) + 2 OH-(aq) xi xf 2xf What is the pH of 5.0 x 10-5 M Mg(OH)2 solution? remember strong bases are 100% dissociating x 0 0 [I] [C] - x + x + 2x x 2x 0 [E] [OH-] = 2x = 2(5.0 x 10-5 M) = 1.0 x 10-4 M pOH = -log[OH-] = 4.00 pH = 14.00 - 4.00 = 10.00

  9. YOUR ACID/BASE FORMULAE: • Kw = [H+][OH-] = 1.0 x 10-14 • The pH and pOH scales goes from 0 - 14. • pH = -log[H+] and[H+] = 10-pH • pOH = -log[OH-] and[OH-] = 10-pOH • pOH + pH =14

  10. Measuring pH There are two ways to measure pH: pH Meters Indicators The [H+] inside the probe (reference electrode) is compared to [H+] outside the probe. Probe must be calibrated first. (inserted into known pH solution)

  11. Indicator: a weak acid or base that undergoes a colourchange when they gain or lose hydrogen ions. • Colour change occurs at various pH depending on indicator • Le Chatelier’s applies to the colour change Natural pH indicators Beets, Blackcurrant juice, Blueberries , Carrots , Cherries , Curry Powder , Grapes , Onion , Petunia Petals , Poison Primrose , Poppy Petals , Red cabbage , Red Radish , Rhubarb , Rose Petals , Strawberries ,Tea , Thyme , Turmeric , Tulip Petals , Violet Petals

  12. Red Litmus stays red in the presence of an acid.

  13. It turns blue in presense of a base.

  14. Phenolphthaleinis a commonly used indicator. • Weak acid is colourless and its conjugate base ion is bright pink

  15. CAN YOU / HAVE YOU? • Formulate an operational definition of pH • Solve problems involving pH • Describe how an acid-base indicator works in terms of colour shifts and Le Chatelier’s Principle Additional KEY Terms

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