Unit 15 Acids & Bases
Acids Hydrochloric Acid HCl Sulfuric Acid H2SO4 Nitric Acid HNO3 Acetic Acid HC2H3O2 Bases Sodium hydroxide NaOH Calcium hydroxide Ca(OH)2 Ammonia NH3 or NH4OH Potassium hydroxide KOH Common Acids & Bases to Memorize
Properties of Acids • Taste sour • React with metals to release H2 (g) • React with bases to form salts and water • Cause a color change in pH indicators (example : litmus turns red in acids)
Properties of Bases • Taste bitter • Feel slippery • React with acids to form salts and water • Cause a color change in pH indicators (example : turn litmus blue)
Arrhenius Theory of Acids & BasesAcids release H+1example: HCl H+1 + Cl-1Bases release OH-1example : NaOH Na+1 + OH-1
Bronsted – Lowry Theory of Acids & BasesAcids donate a proton (H+1)example : HNO3 H+1 + NO3-1Bases accept a protonexample : NH3 + H+1 NH4+1It is hard to see the base in the ammonia NH4OH NH3 + H2O NH4+1 + OH-1
Indicators pH indicators are chemicals which undergo a change in color when there is a change in the pH of a solution. Each pH indicator provides a color over a specific pH range. Example: Phenolphthalein in acid is clear, in base is magenta (pink).
Two factors are involved in determining whether an acid or a base is strong or weak: • Original molarity Example: 0.001 M is very weak 0.1 M is much stronger • Equilibrium constant for the acid or base dissolving in water (the value of Kc) K > 1000 mostly products K = 1 equal amount of reactants and products K < .001 mostly reactants
Strong Acids: Sulfuric acid Ka is very large H2SO4 (aq) 2 H+1(aq) + SO4-2(aq) Hydrochloric acid Ka is very large HCl (aq) H+1(aq) + Cl-1(aq)Weak Acid: Acetic Acid Ka = 1.8 x 10-5 HC2H3O2 (aq) H+1(aq) + C2H3O2-1(aq)
Strong Bases Sodium hydroxide K is very large NaOH(aq) Na+1(aq) + OH-1(aq)Weak Bases Ammonia Kb = 1.8 x 10-5 NH4OH(aq) NH4+1(aq)+ OH-1(aq)Calcium hydroxide Kb = 1.3 x 10-6 Ca(OH)2 (aq) Ca+2 (aq) + 2 OH-1(aq)
A student uses 25 mL of 0.100 M NaOH to titrate with 50 mL of HNO3 of unknown concentration. What is the concentration of the acid?
Microscopic picture of the solutions in the titration of unknown M HNO3 with 0.100 MNaOH.(the problem on the 4th page back) Phenolphthalein pH indicator added to flask
The pH curve for the titration of 50.0 mL of unknown M HNO3 with 0.100 MNaOH.
Titration is a method used to determine the molarity of a solution. A measured volume of the solution with unknown molarity is placed into a flask. A solution with known molarity is slowly poured into the solution until the neutralization point (end point) is reached. The point when :Acid + Base H2O + saltMoles of Acid = Moles of BaseMA VA = MB VBRemember : Moles = (Molarity) (volume in liters)
Titration Procedure1. Label 4 beakers: acid, base, H2O, waste2. Place liquid of known concentration in the burette. A burette is a glass tube that delivers a varied amount of liquid with an accuracy of +0.10 mL. Run some liquid out of the burette until the air bubbles are out of the tip of the burette.3. Pipet 10 mL of unknown concentration solution into an Erlenmeyer flask. A pipet is a glass tube calibrated to deliver an exact amount of liquid. Accuracy is + 0.05 mL. Touch the last drop to the side of the flask.4. Add a few drops of a pH indicator to the flask. Phenolphthalein is often used.5. Run a rapid titration first to obtain a rough estimate of the amount of solution needed to reach the neutralization point. Be sure to record an initial reading and final reading of the solution in the burette.6.Run 2 (or more) slow titrations to obtain accurate data to calculate the molarity of the unknown solution.
Titration of NaOHTitration Lab 1 Microscopic picture of the solutions in the titration of unknown M NaOH with a known MHCl. Solution of HCl H+ Cl- Phenolphthalein pH indicator added to flask Solution of NaOH Na+ OH- MA VA = MB VB
pH is a measure of the amount of acid in solution. It is defined as: pH = -log 10 [H+1]Any H2O solution must follow:H2O(L) H+1(aq) + OH-1(aq)Kw = [H+1] [OH-1] = 1.0 x 10-14[H+1] = 1.0 x 10-7pH of pure H2O = -log10(1.0 x 10-7) = 7
The pH scale.A change from 1 pH unit to the next, the [H+1] changes by a factor of 10!
Calculate the pH of a solution that has the [H+1] of 0.45 M.Calculate the pH of a solution that has the [OH-1] of 0.31 M.Calculate the pH of a solution that is made with 0.84 g KOH mixed in 600 mL of H2O.
Calculating the pH is done using pH = -log10 [H+]If you know the pH, you can calculate the [H+] using10-pH = [H+] Calculate the [H+] if the pH = 5.26Calculate the Molarity of an HCl solution if the pH = 8.22Calculate the Molarity of a NaOH solution if the pH =12.55
A titration was conducted using Acetic acid and Potassium hydroxide. 25.2 mL of acetic acid of .87 M was used to titrate 10 mL of potassium hydroxide. What is the molarity of the potassium hydroxide, and write the chemical equation for the reaction.
Introductory Lab for Acids & Bases • Look at how indicators work, color changes • Find the end point, where the amount of acid and base are equal. At this point, what is left is salt and water. • See activity series of metals. Some metals are more active than others.
Determination of M of VinegarTitration Lab 2 Microscopic picture of the solutions in the titration of unknown M HC2H3O2 with a known MNaOH. Solution of NaOH Na+ OH- Solution of HC2H3O2 Phenolphthalein pH indicator added to flask H+ C2H3O2-
Solid Acid Lab mole acid = mole base grams / molar mass = (M) (liters) (molar mass)(grams) / molar mass = (M)(liters)(molar mass) grams / (M)(liters) = (M) (liters) (molar mass) / (M)(liters) grams / (M)(liters) = (molar mass)
Molar Mass of a solid acidTitration Lab #3Microscopic picture of the solutions in the titration of unknown molar mass solid acid with a known MNaOH. Solution of NaOH Na+ OH- Solution with solid acid Phenolphthalein pH indicator added to flask Ions from solid acid
Review • Just memorize the 8 from your notes • Taste sour, release H+, donate protons, acid + base = salt + water, • Taste bitter, release OH-, accept protons, acid + base = salt + water • Hydrogen, H+1 • Hydroxide, OH-1 • Salt + water • HCl + NaOH H2O + NaCl • HCl H+1 + Cl-1 if HCl is .1 M, then H+1 is also .1 M , -log .1 = pH of 1 • NaOH Na+1 + OH-1 if NaOH is .01 M, then OH-1 is .01 M, you need to use the formula Kw = [H+1][OH-1] = 1 x 10-14 1 x 10-14 / .01 = 1 x 10-12 which is the [H+1] -log1x10-12 = pH of 12 • 0.78 M Matching 1. K 5. M 9. F 13. N 17. L 2. O 6.. P 10. H 14. A 18. Q 3. J 7. D 11. E 15. B 4. G 8. R 12. I 16. C
Down 2. Autoprotolysis 11. Atomic number 49 19. Normal 25. Amphiprotism 38. Methyl Across 10. Alizarin 13. Nonmetals 20. Molality 24. Conjugate 27. Anhydrous 42. Equivalent Bases Crossword
Across 21. Yellow 30. Hydrogen 34. Hydronium 37. Oxidizing Down 3. Corrosive 20. Dehydration 22. Oxyacids Acids Crossword