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TOPIC: pH

Do Now: Identify as acid, base, salt, or covalent Electrolyte or Not. 1. NaCl 2. C 2 H 5 OH 3. H 2 SO 4 4. NaOH 5 . C 12 H 22 O 11 6. CaI 2 7. HF 8. Mg(OH) 2 9. NH 3 10.CH 3 COOH. TOPIC: pH. 6. SALT - ELECTROLYTE. 1. SALT - ELECTROLYTE. 2. COVALENT -NO. 7. ACID- WEAK ELECTROLYTE.

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TOPIC: pH

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  1. Do Now: Identify as acid, base, salt, or covalentElectrolyte or Not 1. NaCl 2. C2H5OH 3. H2SO4 4. NaOH 5. C12H22O11 6. CaI2 7. HF 8. Mg(OH)2 9. NH3 10.CH3COOH TOPIC: pH 6. SALT - ELECTROLYTE 1. SALT - ELECTROLYTE 2. COVALENT -NO 7. ACID- WEAK ELECTROLYTE 8. BASE- ELECTROLYTE 3. ACID- ELECTROLYTE 9. BASE- WEAK ELECTROLYTE 4. BASE- ELECTROLYTE 5. COVALENT -NO 10. ACID- WEAK ELECTROLYTE

  2. Acid, Base, or Neutral • Neutral solution: [H+1] = [OH-1] • Acidic solution: H+1 > OH-1 pH= LESS THEN 7 • Basic solution: OH-1 > H+1 pH= GREATER THEN 7

  3. pH scale measure how acidic/basic a substance is.Ranges from 0-140 more acidic more basic 14more alkaline (another word for basic) Logarithmic scale (based on powers of 10)each decrease of one unit of pH represents a 10x increase inH+ concentrationE: pH 4 is ten times more acidic then pH 5 Ex: pH 10 is ten times more basic then pH 9

  4. Calculating pH • pH=-log [H+] • [H+] = concentration • Ex. 0.01M HCl has a pH of? • pH = -log(0.01) • pH=2

  5. Concentration from pH • Which is more concentrated a HCl solution with a pH or 2 or 3? • pH 2 is 10 times more concentrated (remember changes by 10) • Try it • Antilog (2nd log) 2 = 0.01M • Antilog 3 = 0.001M

  6. Try to remember: The lower the pH – the high the concentration of H+ ions

  7. So how do you find pH of a base? • All you have are OH- ions • ONLY CAN CALC pOH • pOH=-log [OH-] • [OH-] = concentration • pH + pOH = 14 • So 14 – pOH = pH • Ex. 0.01M NaOH has a pH of? • pOH = -log(0.01) • pOH=2 • pH = 14-2 = 12

  8. pH range • 0 to 14 • with 7 being neutral • pH = 0, strongly acidic • pH = 14, strongly basic

  9. Because it’s based on powers of 10 there is a trick • If molarity of acid is .001M =10-3 pH = 3 • If molarity of acid is .00001M = 10-5 pH = 5 • If molarity of base is .001M = 10-3pOH = 3 pH 14-3 = 11 • If molarity of base is .00001M = 10-5pOH = 5 pH 14-5 = 9

  10. Antilog(-pH) = [H+1] Antilog(-4) =1 x 10-4 M pH + pOH = 14 4 + X = 14 X =10 Antilog(-10) = [OH-1] 1x10-10 M = [OH-1] If pH = 4 • [H+1] = ? • pOH = ? • [OH-1] = ?

  11. pH + pOH = 14 X + 3 = 14 X = 11 Antilog(-11) = 1x10-11 M If the [OH-1] = 1 X 10-3 M pOH = -log[OH-1] = -log(10-3) = 3 • pOH = ? • pH = ? • [H+1] = ?

  12. pH=-Log (10-5) =5 pH + pOH =14 5+x =14 X=9 Antilog(-9)= 1x10-9M If the[H+1] = 1 x 10-5 M • The pH = ? • The pOH = ? • The [OH-] = ?

  13. How to safely test pH • Instruments – use a pH meter • Indicators – use a series of indicators • See if the substance reacts with a metal other than Cu, Ag, or Au • NEVER “taste”

  14. Indicator • substance that changes color over narrow pH range • Use several indicators to narrow down pH range of substance

  15. Practice using table M1. What indicator is yellow with a pH 9.82. Which indictor is blue with a pH of 5.6 0-3.0 Orange Green Pink Purple Green Green 3.1.-4.4 4.5-14 7.7-14 8.4-14 0-3.7 3.8-5.4 5.5-14 9.7-14

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