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Titrations

Titrations. Acid-base indicators are…. Compounds whose color is sensitive to pH. Either weak acids or weak bases. pH paper is a universal indicator. It is made by soaking the paper in several different indicators. Phenolphthalein.

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Titrations

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  1. Titrations

  2. Acid-base indicators are… • Compounds whose color is sensitive to pH. • Either weak acids or weak bases. • pH paper is a universal indicator. It is made by soaking the paper in several different indicators.

  3. Phenolphthalein • An indicator that changes color from clear in acid to pink in base (pH 8-10). • This is the indicator that we will use in the lab during titrations.

  4. Titrations • The controlled addition and measurement of the amount of a solution of known concentration (NaOH) required to react completely with a measured amount of a solution of unknown concentration (HCl). • Neutralization: A + B  Salt + H2O • The point of neutralization is the endpoint = change in color of indicator

  5. Good color! Too much base!

  6. Drill #10 5/7, 5/8/14 • Fill in the following table. Need to use your scientific calculator.

  7. 11 3.0 1.0×10-3M 1.0×10-11M 2.0 12 1.0×10-2M 1.0×10-12M 8 6 1×10-8M 1×10-6M 10.8 3.22 6.00×10-4M 1.67×10-11M 13 .70 2.0×10-1M 5.0×10-14M 2.22 11.8 6.00×10-3M 1.67×10-12M

  8. 11 3.0 1.0×10-3M 1.0×10-11M 2.0 12 1.0×10-2M 1.0×10-12M 8 6 1×10-8M 1×10-6M 10.8 3.22 6.00×10-4M 1.67×10-11M 13 .70 2.0×10-1M 5.0×10-14M 2.22 11.8 6.00×10-3M 1.67×10-12M

  9. Agenda • Go over Titration Curve Graph • Acid and Base strength • Titration Calculation Problems • Titration Lab

  10. Homework • Titration Problems • Titration Lab

  11. Titration Curve for strong acid & strong base

  12. Equivalence Point • The point at which the two solutions used in a titration are present in equal amounts • Amount of acid in moles = Amount of base in moles • This can be found using an indicator – in a perfect world, the endpoint (point at which the indicator changes color) would be the same. *Note: this is not the same volume or the same concentration, just the same MOLES

  13. Equivalence Point • Strong acid + strong base = equivalence point at pH of 7 • Strong acid + weak base = equivalence point at pH of <7 • Weak acid + strong base = equivalence point at pH of >7

  14. How to solve titration problems: • Write the balanced neutralization equation • Solve for moles of given (using molarity and volume) • Convert from moles of given to moles of unknown using mole ratio • Use moles of unknown to solve for molarity or volume. NOTE: If moles are equivalent (coefficients) then: MAVA =MBVB

  15. Assignment • Titration Problems

  16. Titration Lab • Place 5 ml of HCl in Erlenmeyer flask • Add 2 drops of phenolphthalein indicator to the flask • Take an initial volume buret reading • Place sheet of white paper under flask during titration • Titrate with .50 M NaOH until you get a pale pink color that stays pink for about 10 secs • Make sure you carefully swirl flask after each titration • If you think you have reached the endpoint, record final volume of NaOH.

  17. Sample Titration Prob • Record calculations on half sheet of paper.

  18. Drill #18 5/24 & 28/13 • A student titrates a 20 ml sample of a solution of HBr with unknown molarity. The titration requires 20.05 ml of a 0.1819 M solution of NaOH. What is the molarity of the HBr solution? • Answer: 0.1824 M • A 35 ml sample of ammonium hydroxide is titrated to the end point with 54.95 ml of a 0.400 M sulfuric acid. What is the molarity of the ammonium hydroxide? • Answer: 1.26 M

  19. Agenda • Go over Review Packet • Test

  20. Drill #16 5/22 & 23/13 Calculate the pH for the following solutions and indicate whether the solution is acidic (A), basic (B), or neutral (N). • [H+] = 1 x 10-2 M • [OH-] = 1 x 10-2 M • [OH-] = 1 x 10-8 M • [H+] = 1 x 10-6 M What are the [OH-] for solutions with the following ph values? 5. 4.0 6. 8.0

  21. Drill #16 5/22 & 23/13 Calculate the pH for the following solutions and indicate whether the solution is acidic (A), basic (B), or neutral (N). • [H+] = 1 x 10-2 M – 2, A • [OH-] = 1 x 10-2 M – 12, B • [OH-] = 1 x 10-8 M – 6, A • [H+] = 1 x 10-6 M – 6, A What are the [OH-] for solutions with the following ph values? 5. pH = 4.0; pOH = 10; [OH-] = 1 x 10-10 M 6. pH = 8.0; pOH = 6; [OH-] = 1 x 10-6 M

  22. Drill #17 5/22 & 23/13Write the names for the following acids and bases: a) KOH b) HF c) H2SO3 d) Fe(OH)2 e) HCN Write the formulas for the following acids: a) phosphorous acid b) hydrobromic acid c) carbonic acid

  23. Drill #17 5/22 & 23/13Write the names for the following acids and bases: a) KOH - potassium hydroxide b) HF - hydrofluoric acid c) H2SO3 - sulfurous acid d) Fe(OH)2 – iron (II) hydroxide e) HCN - hydrocyanic acid or cyanic acid Write the formulas for the following acids: a) phosphorous acid - H3PO3 b) hydrobromic acid - HBr c) carbonic acid - H2CO3

  24. Agenda • Titration Calculations • Titration Lab (4B – postponed until next wk) Announcements • Turn in Naming Bases and Crossword Puzzle • Test next class.

  25. If we know the molarity and the volume of acid used, then can we calculate the amount of moles of acid? How? • MolA = MAVA

  26. Worksheet!

  27. Green workbook, pg. 272 -275

  28. Test Topics • Properties of acids, bases, and salts • Bronsted-Lowry definition of acids/bases • Amphoteric substance • Neutralization reaction – must be balanced • Purpose of calculating an Acid or Base dissociation constant • Naming acids • Equations for pH, pOH, [H+], and [OH-] • Titration calculations

  29. Objective • SWBAT calculate molarity of acid using data from titration.

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