23_AcidBaseTitrationsFall2023Complete

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23. Acid-Base Titrations CH 229 – General Chemistry Laboratory Acid-base titrations – p. 1 CH 229 – General Chemistry Laboratory What will you be working on this week? Post-lab from Conductivity and pH of aqueous solutions due before beginning of lab. This weeks lab Prelab due before lab as usual. Procedure is NOT in your lab manual. See “AcidBaseTitration.pdf” Week 5 module on Canvas. Printed copies will be available in lab. Please leave so we can reuse them. Together with next week’s lab covers the topic of the lab practicum. This week is particularly close to the lab practicum. Remember, the practicum is open notebook so keep a good notebook. INDIVIDUAL EXCEL REPORTING SHEET DUE AT END OF LAB (no other post-lab work). Must be xls or xlsx format. Acid-base titrations – p. 2 CH 229 – General Chemistry Laboratory

What will you be working on this week (cont)? Introduction for next week’s lab This cover’s lab 24 in your lab manual – Antacid Effectiveness Introduction due before start of next week’s lab Specific instructions are provided on writing the introduction. See “Lab24_IntroductionAssignmentFall2023.pdf” under week 5 module. Prelab due as usual before beginning of lab next week. Acid-base titrations – p. 3 CH 229 – General Chemistry Laboratory This is mostly an individual lab. It is completed at the end of the lab period Each individual must fill out an excel reporting sheet due at the end of lab. Acid-base titrations – p. 4 CH 229 – General Chemistry Laboratory

What is a titration? Titration Analytical technique where the volume of a solution required to produce a given reaction with a known volume of another solution is measured. Primarily used to determine the concentration of one solution when the concentration of the other is known Also used to determine equilibrium properties of chemical reactions, notably the acid dissociation constant of a weak acid or base. Acid-base titrations – p. 5 CH 229 – General Chemistry Laboratory Terminology titrant in buret analyte Titrant The solution, typically of known concentration (standardized), that is added to another solution, typically to determine its concentration. Analyte The solution, typically of unknown concentration, to which the titrant is added. Buret A graduated glass cylinder with a stopcock (used to stop or start the flow of liquid). Used in a titration to measure the volume of titrant added. Acid-base titrations – p. 6 CH 229 – General Chemistry Laboratory

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Acid/base titration Based on an acid/base neutralization reaction: HCl(aq) + NaOH(aq) → H 2 O(l) + NaCl(aq) If at least one of the acid or base is strong, the reaction goes to completion. Acid-base titrations – p. 7 CH 229 – General Chemistry Laboratory e.g. – Titrate HCl analyte of unkonwn concentration with NaOH(aq) titrant of known concentration NaOH of known concentration HCl [?] Measure volume of titrant required to completely neu- tralize the analyte. HCl(aq) + NaOH(aq) → H 2 O(l) + NaCl(aq) This volume is the equivalence point. At the equivalence point: n HCl = n NaOH M HCl V HCl = M NaOH V NaOH M HCl = M NaOH V NaOH V NaOH Acid-base titrations – p. 8 CH 229 – General Chemistry Laboratory

Clicker What volume of NaOH is needed to reach the equivalence point? [NaOH] = 0.010 M 100 mL of 0.0010 M HCl A 1 mL B 10 mL C 100 mL D 1000 mL Acid-base titrations – p. 8 CH 229 – General Chemistry Laboratory Indicator used to estimate the equivalence point pH 3 4 5 6 7 8 9 10 n init HCl 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 mmol V added NaOH 0 8.91 9.89 9.99 10.00 10.01 10.11 11.11 mL n added NaOH 0 0.0891 0.0989 0.0999 0.10 0.1001 0.1011 0.1111 mmol n left HCl 0.1 0.0109 0.0011 0.0001 0.0000 0.0000 0.0000 0.0000 mmol n left NaOH 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0011 0.0111 mmol Acid-base titrations – p. 9 CH 229 – General Chemistry Laboratory

Equivalence point versus end point Equivalence point: the volume of titrant required to completely neutralize the analyte. End point: the volume of titrant required to cause the indicator to change color. Acid-base titrations – p. 10 CH 229 – General Chemistry Laboratory Equivalence point volume can be measured because of the rapid change in pH that occurs Acid-base titrations – p. 11 CH 229 – General Chemistry Laboratory

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Standardizing sodium hydroxide titrant NaOH, [?] known amount of KHP in water potassium hydrogen phthalate (KHP), C 8 H 5 KO 4 weigh out known amount of KHP Measure volume of NaOH to reach end point Acid-base titrations – p. 12 CH 229 – General Chemistry Laboratory Neutralization of potassium hydrogen phthalate C C C C C C H H H H C O OH C O - K + O one ionizable proton molar mass = 204.222 g mol - 1 KHP(s) → K + (aq) + HP - (aq) HP - (aq)+OH - (aq) → P 2 - (aq)+H 2 O(l) At equivalence point: n KHP = n NaOH mass of KHP known so n KHP known Volume of NaOH known so [NaOH] = n NaOH / V NaOH known Acid-base titrations – p. 13 CH 229 – General Chemistry Laboratory

Clicker A sample of 0.40 g KHP takes 9.8 mL (crude titration) of NaOH to neutralize. What is the concentration of NaOH? 1 How many moles of KHP are there? 2 How many moles of NaOH are needed to neutralize the moles of KHP? 3 What is the concentration of the NaOH? Acid-base titrations – p. 14 CH 229 – General Chemistry Laboratory Step 1: How many moles of KHP? Acid-base titrations – p. 15 CH 229 – General Chemistry Laboratory

Step 1: How many moles of KHP? 0 . 40 g KHP 1 mol KHP 204 . 22 g KHP = 0 . 001959 mol KHP Acid-base titrations – p. 16 CH 229 – General Chemistry Laboratory Step 2: How many moles of NaOH? Acid-base titrations – p. 17 CH 229 – General Chemistry Laboratory

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Step 2: How many moles of NaOH? At eq. pt: n NaOH = n KHP = 0.001959 mol Acid-base titrations – p. 18 CH 229 – General Chemistry Laboratory Step 3: What [NaOH]? [NaOH] = n NaOH V NaOH = 0 . 001959mol 9 . 8mL 1000mL 1L = 0 . 1999 = 0 . 20M Acid-base titrations – p. 19 CH 229 – General Chemistry Laboratory

Tips - will also help you do well on practicum 1 Condition your buret 2 Make sure you are not delivering air in place of titrant 3 Read bottom of meniscus to at least 0.05 mL Drain some titrant to make sure buret tip is filled Use the same process to remove any air bubbles 4 Make sure everything leaving buret reacts Rinse tip of buret into analyte flask with wash bottle Rinse sides of analyte flask with wash bottle Swirl analyte solution 5 Make very small additions near the equivalence point. Turn stopcock 180 ◦ quickly to dispense a small amount. Gradually turn the stopcock until just a drop is dispensed. 6 Clean up - water added then drained should have pH = 7 Acid-base titrations – p. 20 CH 229 – General Chemistry Laboratory Conditioning buret Check for cleanliness – fill (stopcock closed) with water to above 0.00 mL mark and then drain the water smooth interior sides signals a clean buret, water droplets sticking to the sides indicates a dirty buret. Condition – Add 5 mL of reagent to empty buret (with stopcock closed) Drain about 2 mL out tip. Slowly pour the remainder out the top while rotating buret to wash sides Repeat 2 more times. Acid-base titrations – p. 21 CH 229 – General Chemistry Laboratory

Reading buret 22 23 24 25 24.05 mL Read bottom of meniscus Read to at least 0.05 mL avoid paralax – read looking from the same level as the meniscus Note graduations goes from 0.00 at top to 25.00 at bottom. Acid-base titrations – p. 22 CH 229 – General Chemistry Laboratory Speeding up your work without overshooting Trial titration to estimate end-point volume. or calculate the approximate end-point volume if possible. Generally, you can add 80% of volume from one of the above and then slow your addition near the end point. Don’t overshoot! end point little over end point Acid-base titrations – p. 23 CH 229 – General Chemistry Laboratory

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Acid-base titrations – p. 24 CH 229 – General Chemistry Laboratory Clicker What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq)? The molar mass of KHP is 204.222 g / mol - 1 Part 1 : How many moles of KHP are there? Part 2 : How many moles of NaOH are needed to neutralize the KHP? Part 3 : What volume of 0.2M NaOH(aq) contains ?? mol? Acid-base titrations – p. 24 CH 229 – General Chemistry Laboratory

First why 0.83 g KHP? 0.40 g took 9.8 mL. Not optimal given the volume of the buret is 25.00 mL Better to have titrant volume near 75% of buret volume. 0 . 83 g 0 . 40 g == x mL 9 . 8 mL x = 20 . 33 mL Acid-base titrations – p. 25 CH 229 – General Chemistry Laboratory Clicker What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq))? The molar mass of KHP is 204.222 g / mol - 1 Part 1: How many moles of KHP are there? A 0.166 mol B 0.00406 mol C 0.83 mol D 169.6 mol Acid-base titrations – p. 25 CH 229 – General Chemistry Laboratory

What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq))? The molar mass of KHP is 204.222 g / mol - 1 Part 1: How many moles of KHP are there? A 0.166 mol B 0.00406 mol C 0.83 mol D 169.6 mol 0 . 83 g KHP 1 mol KHP 204 . 222 g KHP = 0 . 00406 mol Acid-base titrations – p. 26 CH 229 – General Chemistry Laboratory What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq))? The molar mass of KHP is 204.222 g / mol - 1 Part 1: How many moles of KHP are there? A 0.166 mol B 0.00406 mol C 0.83 mol D 169.6 mol 0 . 83 g KHP 1 mol KHP 204 . 222 g KHP = 0 . 00406 mol Part 2: How many moles of NaOH are needed to neutralize the KHP? Answer: 0.00406 mol Acid-base titrations – p. 27 CH 229 – General Chemistry Laboratory

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Clicker What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq))? The molar mass of KHP is 204.222 g / mol - 1 Part 3 What volume of 0.20M NaOH(aq) contains 0.00406 mol of NaOH(aq)? A 49.26 mL B 0.812 mL C 0.020 mL D 20.3 mL Acid-base titrations – p. 27 CH 229 – General Chemistry Laboratory What volume of 0.20 M NaOH(aq) is needed to precisely neutralize 0.83 g of KHP (i.e. What is the equivalence point volume for titrating 0.83 g of KHP with 0.20 M NaOH(aq))? The molar mass of KHP is 204.222 g / mol - 1 Part 3 What volume of 0.20M NaOH(aq) contains 0.00406 mol of NaOH(? A 49.26 mL B 0.812 mL C 0.020 mL D 20.3 mL 0 . 00406 mol NaOH L NaOH(aq) 0 . 20 mol NaOH 1 L NaOH(aq) 1 × 10 - 3 mL NaOH(sq) = 20 . 3 mL Acid-base titrations – p. 28 CH 229 – General Chemistry Laboratory