2 The Big PictureUse a solution of known concentration (the standard solution) to determine the concentration of an unknown solution
3 What we need The chemical equation A way to measure amounts of solution addedFixed and variableA way to determine that the titration is completeReaction should be fast
4 NaOH(aq) + H2SO4(aq) Na2SO4(aq) + H2O(l) The Chemical ReactionMust know the equation and correct stoichiometric ratiosExample:Write the equation for the titration of sulfuric acid with sodium hydroxideNaOH(aq) + H2SO4(aq) Na2SO4(aq) + H2O(l)22Not balancedTherefore the base to acid ratio is 2:1
5 Volume MeasurementsTitrate a variable amount of solution into a known volume of solution until titration is completeFixed (known) volume should be measured with high precision:Use pipette (p.17)Variable volume should be as high precision as possible: Use burette
6 How to determine titration is complete Usually an indicator is usedTermsEnd point: when indicator changes colorEquivalence point: when a stoichio-metrically equivalent amount of titrant has been added to solution
7 Phenolphthalein is a very common acid-base indicator More on indicatorsPhenolphthalein is a very common acid-base indicatorColorless in acidPink in base
8 Example25.00 mL of M sulfuric acid is titrated with NaOH, requiring mL to reach the endpoint. What is the NaOH concentration?
9 2 NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2 H2O(l) ExampleWe place mL of acid and a couple drops of the indicator into the flask and titrate with base until the solution turns slightly pink.2 NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2 H2O(l)
10 Example25.00 mL of M sulfuric acid is titrated with NaOH, requiring mL to reach the endpoint. What is the NaOH concentration?
11 ExampleMoles of acidMoles of baseConcentration of base
12 Some Titration Techniques Start with burette at or beyond 0.00 mLIt doesn’t matter, just record it!Don’t waste time getting exactly 0.00 mLTitrate to the ½ dropAdd extra water if neededHow does this affect calculations?
13 Some Titration Techniques Stir!Place on white paperPalest and most reproducible pink possible
14 Common Abbreviations for Acetic Acid CH3COOHHCH3CO2C2H4O2C2H3O2HHOAc
15 This Week’s AnalysisGoal: Determine molar concentration and mass percentage acetic acid in vinegarUnits of concentration of acetic acid in vinegar:Units on mass % of acetic acid in vinegar:
16 This Week’s Analysis Oxalic acid as a primary standard Why?One oxalic acid solution per 2 groupsNote that oxalic acid is a hydrateHow does this affect you?10 mL pipettes250 mL volumetric flasks
17 Procedure ProposalHow you will prepare your oxalic acid solution (~0.25 M)How you will determine NaOH concentration including calculations and chemical reactionsHow you will determine the concentration of the acetic acid in vinegar (and how many trials)Road map of calculations for calculating C and mass % acetic acid from your dataDon’t even think of using C1V1=C2V2
18 This investigation, Author 3: Introduction and Conclusion1: Discussion2: Data/Results and ExperimentalA: Introduction, Conclusion, Data/ResultsB: Discussion and Experimental