1. Acid / Base Titration Professor Bob Kaplan University Department of Science

2. The most distinctive feature of an acidic or basic compound is ionic dissociation.  Compounds dissociate into their individual cations and anions. Acids  H+ cations Bases  OH- anions

3. Strength of an acidic or basic compound is determined by the degree of dissociation. Less stable compound  More ionic dissociation  More charged ions in solution  Stronger acid or base

4. HCL  H+ + Cl- Strong acid driven to products. Products produced includes: H+ cations More products ( more H+ )  Stronger acid Strong acids dissociate completely to form products.

5. pH indicates degree of dissociation. pH measures the concentration of H+ ions. ph  [ H+ ] pOH  [ OH- ]

6. ph = - log [ H + ] [ H + ] = 0.1 M = 10 -1 M log 10 -1 = - 1 - log = 1 [ H + ] = 0.000001 M = 10 -6 M log 10 -6 = - 6 - log = 6 Lower pH  Higher Acidity

7. Strong acids dissociate to products HCL  H+ + Cl- Measure strengths by Dissociation Constant K =

8. Larger K  Higher [ H + ] Smaller K  Lower [ H+ ] Stronger acid  Higher [ H + ] Larger K  Stronger acid

9. NaOH  Na+ + OH- K = Larger K  Higher [ OH - ] Larger K  Stronger base

10. Sulfuric Acid H2SO4 --> 2 H+ + SO4 2 protons liberated per molecule. Phosphoric acid (in soda pop) H3PO4 --> 3 H+ + PO4 3 protons liberated per molecule !

11. Acids produce H+ cations HCl = H+ + Cl- Each mole of HCL produces 1 mole of H+ Bases produce OH- anions NaOH = Na+ + OH- Each mole of NaOH produces I mole OH-

12. H+ + OH- = H2O pH 7 = neutral point ph 7: [ H+ ] = [ OH- ] = 10 -7 Ionic concentrations are equal.

13. Investigate the strength of 5 different commercial antacids by chemical titration. A titration is a controlled way of measuring the amount of acid it takes to neutralize the base. If you know how much base is used, then you can tell how much acid is present. Using HCl and NaOH as our acid and base, All mole ratios are 1:1.

14. In the chemistry laboratory, we use volumetric measurement for solutions. Examples include: Beakers, flasks, burettes, pipettes, eye droppers Typically in liters (L) or milliliters (mL) Control the volume of acid or base using a stopcock 1-way valve at the base of a calibrated buret in order to deliver the solution of acid or base drop-by-drop.

15. Measurement of the concentration of solution. M = Molarity Molar concentration = moles / liter = M Measure volume in liters (or milliliters ml) Vol ( L ) x Conc. ( mol / L ) = Number of Moles

16. Our objective is to determine how much base is in each antacid tablet. To determine this indirectly:  Neutralize the base with an acid. Since we have a 1 : 1 ratio of acid : base Number of moles of acid added = Number of moles base in antacid tablet

17. Begin by adding extra acid. Add 40 mL of 0.1 molar HCl to each one How many moles of acid is that ? ( 40 mL ) * ( 1 liter / 1000 mL ) = 0.040 liters Vol. x Conc. = Moles ( 0.040 liters ) ( 0.1 moles / liter ) = 0.004 moles

18. View this 0.004 moles HCl as stomach acid. That is the total amount of stomach acid after dinner tonight. Then eat one tablets But one tablet is not enough. So in order to neutralize all of the acid,  Add MORE base. The strongest tablet (base) will require the least addition of more base.

19. The strongest tablet will already have the most base and will thus require the least addition of more base (NaOH). That is the key to the first question. Thus, there are no calculations necessary. It is purely qualitative. Compare volumes of added NaOH

20. Not all tablets weigh the same amount. Break it down to a "per gram" basis Change the volume added to: Moles per gram Moles added / gram dosage

21. Maalox requires 24.1 mL NaOH NaOH Concentration = [ NaOH ] = 0.05 M Molarity = M = moles / liter ( 0.024 L ) x ( 0.05 moles / liter) = 1.21 x 10 -3 Moles

22. Consider the weight of each tablet in grams Maalox: 20.0 grams Want moles / gram Divide the number of moles by the weight of that tablet in grams [ 1.21 x 10 -3 moles ] / 20 grams = 6.05 x 10 -5 mol / g

23. So which is the strongest antacid tablet on a per gram basis ? Which tablet requires the least amount of acid to neutralize the base in the tablet ….. …..in moles / gram ?

24. See the following websites: http://en.wikipedia.org/wiki/Acid- base_titration http://en.wikipedia.org/wiki/PH_indicator

25. H2SO4 is a diprotic acid. It releases 2 protons (H+) per acid molecule. H2SO4 = 2 H+ + SO4 (2-) Thus, it is likely to be at least twice as strong. Thus, at the same concentration (0.1 M), we need to add only half as much acid.

26. Balance the equation: Al (OH)3 + HCl  AlCl3 + H2O *Hint: There are 3 hydrogen atoms on the left, and only 1 H atom on the right  3 H2O needed on the right.