WEEK 6 PROCEDURE OF TITRATIONS ACID-BASE TITRATIONS

What is acid-base titration? A TITRATION WHICH DEALS WITH A REACTION INVOLVING ACID AND A BASE. What is a titration? The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration.

What is a standard solution? A standard solution is one whose concentration is precisely known. What is a test solution? A test solution is one whose concentration is to be estimated

Titration of Vinegar against NaOH Vinegar is an acetic acid solution of certain concentration So a titration of vinegar against NaOH actually means, a reaction between acetic acid and NaOH. HC2H3O2(aq) + NaOH(aq)  NaC2H3O2 + H2O(l) Sodium hydroxide Sodium Acetate Acetic acid water water Acid Base salt

Titration of Vinegar against NaOH HC2H3O2(aq) + NaOH(aq)  NaC2H3O2 + H2O(l) CH3COOH(aq) + NaOH(aq)  CH3COONa + H2O(l) 1 molecule 1 molecule 1 molecule 1 molecule 1 mole 1 mole 1 mole 1 mole 1 mole CH3COOH ≡ 1 mole NaOH

Titration of Vinegar against NaOH In this experiment, we are trying to find the [CH3COOH] in vinegar. So we have to know the [NaOH] accurately first, before finding the [CH3COOH] in Vinegar. Finding the [NaOH] should be pretty easy right?!!

How hard is it to make 500 mL of 0.1 M NaOH? Should not be that hard right?!! Calculate the weight of NaOH (2.0 g) Weigh out the NaOH on the balance Dissolve it in 500 mL of water in a volumetric flask Hold on! We have a problem here!!

So what is your problem? What do you mean by hygroscopic? I don’t have a problem but Mr. NaOH seems to have a problem here NaOH is hygroscopic.. What do you mean by hygroscopic? It absorbs moisture. NaOH absorbs moisture from air.

What if NaOH is hygroscopic? Let us say, for the problem at hand, we need 2.0 g NaOH to make a 0.1 M NaOH solution. By the time we weigh out the NaOH for our solution, it would have absorbed moisture. So the total weight of 2.0 g is not all due to NaOH. It has some contribution from the water that the NaOH absorbed.

How do we find the [NaOH] precisely? What is standardization? Through standardization What is standardization? It is just a technical term for doing a titration using a primary standard to find the precise concentration of a secondary standard.

What is a primary standard? A primary standard should possess the following qualities: (i) It must be available in very pure form (ii) It should not be affected by exposure to moisture or air. (iii) It should maintain its purity during storage. (iv) The reactions involving the primary standard should be stoichiometric and fast. (v) It should have high molecular weight.

Which primary standard are we going to use? Potassium hydrogen phthalate, abbreviated as KHP. Remember!! KHP is not the molecular formula for Potassium hyrogen phthalate. It is just an abbreviation. So when calculating the molecular weight of KHP, do not add up the atomic weights of K, H and P. COOH C-H COOK CH HC Potassium Hydrogen Phthalate, KHC8H4O4

Standardization KHC8H4O4(aq) + NaOH(aq)  KNaC8H4O4 + H2O(l) water Acid Base salt 1 molecule 1 molecule 1 molecule 1 molecule 1 mole 1 mole 1 mole 1 mole 1 mole KHC8H4O4 ≡ 1 mole NaOH

Standardization Vfinal- Vinital= Vused (in mL) Vinitial moles of KHP = Moles of NaOH moles of KHP = MNaOH × VNaOH “ 0.1 M NaOH ” Vfinal moles of KHP = MNaOH × Vused End point: Pale Permanent Pink color 250mL 250mL 250mL KHP + H2O+ 2-3 drops of phenolphthalein

Titration of Vinegar vs. NaOH Vfinal- Vinital= Vused (in mL) Vinitial moles of acetic acid = Moles of NaOH moles of acetic acid = MNaOH × VNaOH “ 0.1 M NaOH ” Vfinal moles of acetic acid = MNaOH × Vused End point: Pale Permanent Pink color 250mL 250mL 250mL vinegar + H2O+ 2-3 drops of phenolphthalein

Titration Basics First Derivative Curve Shows where change is greatest Titration = addition of a measurable volume of a known solution (titrant) to an unknown solution until it is just consumed Use the stoichiometry of the reaction of the known and unknown to calculate the concentration of the unknown solution A pH curve shows the change in pH versus volume of titrant as the titration proceeds pH meter can be used to monitor pH during the titration 2) An acid-base indicator can be used to signal reaching the equivalence point First Derivative Curve Shows where change is greatest

3) Important points: pH increases slowly far from the equivalence point pH changes quickly near the equivalence point The equivalence point of a strong acid—strong base titration = 7.00

Titration Curves  A titration curve is a graph of the pH changes that occur during an acid-base titration versus the volume of acid or base added. There are three types of titration curves. You need to be able to recognize each and then choose a suitable indicator for that titration.   The equivalence point is the end of a titration where the stoichiometry of the reaction is exactly satisfied, or moles H+ = moles OH-. The transition point refers to when an indicator changes color and [HInd] = [Ind-].

Choosing an Indicator When you choose an indicator, you must pick one so that the transition point of the indicator matches the equivalence point of the titration. When acid base titration is at the equivalence point, the acid has neutralized the base leaving only a salt and water. The pH of the equivalence point depends on type of salt.   Rule of thumb If the salt is neutral the equivalence point = 7 If the salt is basic the equivalence point = 9 If the salt is acidic the equivalence point = 5

1. Titration Curve: Strong Acid and Strong Base   HCl + KOH →

1. Titration Curve: Strong Acid and Strong Base   HCl + KOH → KCl + HOH

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH Indicator

1. Titration Curve: Strong Acid and Strong Base   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue

1. Titration Curve: Strong Acid and Strong Base   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 25 50

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 0.10 M HCl 25 50

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 0.10 M HCl Neutral Salt 25 50

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 0.10 M KOH 0.10 M HCl Neutral Salt 25 50

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 25 50

1. Titration Curve: Strong Acid and Strong Base HCl + KOH → KCl + HOH   HCl + KOH → KCl + HOH Indicator pH = 7 Bromothymol Blue 50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl pH Volume .10 M KOH added 14 7 25 50

2. Titration Curve: Weak Acid and Strong Base   HCN + KOH →

2. Titration Curve: Weak Acid and Strong Base   HCN + KOH → KCN + HOH

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 1.0 M KOH 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 1.0 M KOH Basic Salt 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 1.0 M KOH Basic Salt 1.0 M HCN 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 1.0 M KOH Basic Salt 1.0 M HCN 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH pH Volume 1.0 M HCN added 14 7 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH Buffer Zone pH Volume 1.0 M HCN added 14 7 10 20

2. Titration Curve: Weak Acid and Strong Base HCN + KOH → KCN + HOH Indicator pH = 9 Phenolphthalein 20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH Buffer Zone Weak Acid & Salt are present pH Volume 1.0 M HCN added 14 7 10 20

3. Titration Curve: Strong Acid and Weak Base   HCl + NH3 →

3. Titration Curve: Strong Acid and Weak Base   HCl + NH3 → NH4+ + Cl-

3. Titration Curve: Strong Acid and Weak Base   HCl + NH3 → NH4+ + Cl- Indicator

3. Titration Curve: Strong Acid and Weak Base   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red

3. Titration Curve: Strong Acid and Weak Base   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 30 60

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 1.0 M HCl 30 60

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 1.0 M HCl Acid Salt 30 60

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 1.0 M NH3 1.0 M HCl Acid Salt 30 60

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 30 60 1.0 M NH3 1.0 M HCl Acid Salt

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 30 60

3. Titration Curve: Strong Acid and Weak Base HCl + NH3 → NH4+ + Cl-   HCl + NH3 → NH4+ + Cl- Indicator pH = 5 Methyl Red 60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl pH Volume 1.0 M NH3 added 14 7 Buffer Zone Weak Base & Salt are present 30 60

4. Match the Curve with the Reaction pH Volume .10 M KOH added 14 7 25 50 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

4. Match the Curve with the Reaction pH Volume .10 M KOH added 14 7 25 50 Bisect the verticle pH = 7 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

4. Match the Curve with the Reaction pH Volume .10 M KOH added 14 7 25 50 Bisect the verticle pH = 7 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

5. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 30 60 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

5. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 Bisect the verticle pH = 5 30 60 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

6. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 30 60 A. 3HCl + Al(OH)3 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

6. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 Bisect the verticle pH = 9 30 60 A. 3HCl + Al(OH)2 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH

6. Match the Curve with the Reaction pH Volume 1.0 M NH3 added 14 7 Bisect the verticle pH = 9 30 60 A. 3HCl + Al(OH)2 → AlCl3 + 3HOH B. HCl + KOH → KCl + HOH C. HCN + KOH → KCN + HOH