pH Scales and Calculating pH Levels
Explore the basics of pH, distinguishing between acids, bases, salts, and covalent compounds. Learn about the pH scale, calculating pH levels, and determining concentration based on pH values in this informative content.
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Presentation Transcript
TOPIC: pH Do Now: Identify as acid, base, salt, or covalent Electrolyte or Not 1. NaCl 6. CaI2 7. HF 6. SALT - ELECTROLYTE 1. SALT - ELECTROLYTE 2. C2H5OH 3. H2SO4 4. NaOH 2. COVALENT -NO 7. ACID- WEAK ELECTROLYTE 8. Mg(OH)2 9. NH3 10.CH3COOH 8. BASE- ELECTROLYTE 3. ACID- ELECTROLYTE 9. BASE- WEAK ELECTROLYTE 4. BASE- ELECTROLYTE 5. C12H22O11 5. COVALENT -NO 10. ACID- WEAK ELECTROLYTE
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
pH scale measure how acidic/basic a substance is. Ranges from 0-14 0 more acidic more alkaline (another word for basic) Logarithmic scale (based on powers of 10) each decrease of one unit of pH represents a 10x increase in H+ concentration E: pH 4 is ten times more acidic then pH 5 Ex: pH 10 is ten times more basic then pH 9 more basic 14
Calculating pH pH=-log [H+] [H+] = concentration Ex. 0.01M HCl has a pH of? pH = -log(0.01) pH=2
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
Try to remember: The lower the pH the high the concentration of H+ ions
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
pH range 0 to 14 with 7 being neutral pH = 0, strongly acidic pH = 14, strongly basic
Because its 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 = 10-3 pOH = 3 pH 14-3 = 11 If molarity of base is .00001M = 10-5 pOH = 5 pH 14-5 = 9
If pH = 4 Antilog(-pH) = [H+1] Antilog(-4) = 1 x 10-4 M [H+1] = ? pH + pOH = 14 4 + X = 14 X =10 pOH = ? [OH-1] = ? Antilog(-10) = [OH-1] 1x10-10 M = [OH-1]
If the [OH-1] = 1 X 10-3 M pOH = -log[OH-1] = -log(10-3) = 3 pOH = ? pH = ? pH + pOH = 14 X + 3 = 14 X = 11 [H+1] = ? Antilog(-11) = 1x10-11 M
If the [H+1] = 1 x 10-5 M The pH = ? pH=-Log (10-5) =5 pH + pOH =14 5+x =14 X=9 Antilog(-9)= 1x10-9M The pOH = ? The [OH-] = ?
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
Indicator substance that changes color over narrow pH range Use several indicators to narrow down pH range of substance
Practice using table M 1. What indicator is yellow with a pH 9.8 2. Which indictor is blue with a pH of 5.6 0-3.0 4.5-14 3.1.-4.4 Orange Green Pink 7.7-14 8.4-14 Purple 3.8-5.4 0-3.7 5.5-14 Green 9.7-14 Green
