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Notes- Acids and Bases

Notes- Acids and Bases. Acids and Bases. Arrhenius ACIDS – produces hydrogen ions in aqueous solutions, sour taste, low pH, and the fact that they turn litmus paper red HCl (aq)  H + (aq) + Cl - (aq)

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Notes- Acids and Bases

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  1. Notes-Acids and Bases

  2. Acids and Bases Arrhenius ACIDS – produces hydrogen ions in aqueous solutions, sour taste, low pH, and the fact that they turn litmus paper red HCl (aq) H+(aq) + Cl-(aq) Arrhenius BASES – produces hydroxide ions in aqueous solutions, bitter taste, slippery feel, high pH, and the fact that they turn litmus paper blue NaOH (aq) Na+(aq) + OH-(aq) Arrhenius definition – limits the concept of a base

  3. proton donor proton acceptor Bronsted – Lowry definition – gives a broader definition of a base Bronsted – Lowry ACID – a proton (H+) donor Bronsted – Lowry BASE – a proton (H+) acceptor General Reaction – HA (aq) + H2O (l) H3O+(aq) + A-(aq) Acid Base Conjugate Conjugate Acid Base Conjugate Base – everything that remains of the acid molecule after a proton is lost Conjugate Acid – the base with the transferred proton (H+) Conjugate Acid – Base Pair – two substances related to each other by the donating and accepting of a single proton

  4. Examples: Finish each equation and identify each member of the conjugate acid –base pair. H2SO4(aq) + H2O (l) HSO4-1(aq) + H3O+ (aq) Conjugate Base Conjugate Acid Acid Base CO32-(aq) + H2O (l) HCO3-1(aq) + OH- (aq) Conjugate Acid Conjugate Base Base Acid The hydronium ion, H3O+, forms when water behaves as a base. This happens when the two unshared pairs of electrons on O bond covalently with the H+.

  5. Water as an Acid and a Base Amphoteric – a substance that can behave as either an acid or a base - water is the most common amphoteric substance Ionization of Water – H2O (l) + H2O (l) H3O+(aq) + OH-(aq) In the shorthand form: H2O (l) H+(aq) + OH-(aq)

  6. Ion-product constant – Kw refers to the ionization of water Kw = [H+][OH-] At 25C, Kw = [H+][OH-] = [1.0 x 10-7] [1.0 x 10-7] = 1.0 x 10-14 If [H+] increases, the [OH-] decreases, so the products of the two is still 1.0 x 10-14. There are three possible situations – • A neutral solution, where [H+] = [OH-] • An acidic solution, where [H+]  [OH-] • A basic solution, where [H+]  [OH-]

  7. Example: Calculate [H+] or [OH-] as required for each of the following solutions at 25C, for each solution state whether it is neutral, acidic, or basic. a. 1.0 x 10-5 M OH- b. 10.0 M H+ Kw = [H+][OH-] Kw = [H+][OH-] 1 x 10-14 = [H+][1.0 x 10-5 M] 1 x 10-14 = [10.0 M][OH-] [H+] = 1.0 x 10-9 M [OH-] = 1.00 x 10-15 M BASIC ACIDIC

  8. pH scale pH scale – because the [H+] in an aqueous solution is typically small, logarithms are used to express solution acidity pH = -log [H+] pOH = -log [OH-] Graphing calculator Non graphing calculator 1. Press the +/- key 1. Enter the [H+] 2. Press the log key 2. Press the log key 3. Enter the [H+] 3. Press the +/- key Significant Figure Rule – The number of places to the right of the decimal for a log must be equal to the number of significant figures in the original number.

  9. pH Scale

  10. Example – Calculate the pH or pOH a. [H+] = 1.0 x 10-9 M b. [OH-] = 1.0 x 10-6 M pH = - log [H+] pOH = - log [OH-] pH = - log (1.0 x 10-9 M) pOH = - log (1.0 x 10-6 M) pH = 9.00 pOH = 6.00

  11. Example – Calculate the pH and pOH if the concentration of OH-1 is1.0 x 10-3 M pOH = - log [OH-] Kw = [H+][OH-] pOH = - log (1.0 x 10-3 M) 1 x 10-14 = [H+][1.0 x 10-3 M] [H+] = 1.0 x 10-11 M pOH = 3.00 pH = - log [H+] pH = - log (1.0 x 10-11 M) pH = 11.00

  12. Since Kw = [H+][OH-] = 1.0 x 10-14, pH + pOH = 14.00 Example - The pH of blood is about 7.4. What is the pOH of blood? pH + pOH =14.00 7.4 + pOH = 14.00 pOH = 6.6

  13. In order to calculate the concentration from the pH or pOH, [H+] = 10-pH [OH-] = 10-pOH Graphing calculator Non-graphing calculator • Press the 2nd 1. Enter the pH function, then log 2. Press the +/- key 2. Press the +/- key 3. Press the inverse 3. Enter the pH log key

  14. Example - The pH of a human blood sample was measured to be 7.41. What is the [H+] in blood? [H+] = 10-pH [H+] = 10-7.41 [H+] = 3.9 x 10-8 M

  15. Example – The pOH of the water in a fish tank is found to be 6.59. What is the [H+] for this water? [OH-] = 10-pOH [OH-] = 10-6.59 [OH-] = 2.6 x 10-7 M Kw = [H+][OH-] 1 x 10-14 = [H+][2.6 x 10-7 M] [H+] = 3.8 x 10-8 M

  16. How Do We Measure pH? • For less accurate measurements, one can use • Litmus paper • “Red” paper turns blue above ~pH = 8 • “Blue” paper turns red below ~pH = 5 • An indicator

  17. How Do We Measure pH? For more accurate measurements, one uses a pH meter, which measures the voltage in the solution.

  18. Strong Acids • seven strong acids are HCl, HBr, HI, HNO3, H2SO4, HClO3, and HClO4. • These are, by definition, strong electrolytes and exist totally as ions in aqueous solution.

  19. Strong Bases • Strong bases are the soluble hydroxides, which are the alkali metal and heavier alkaline earth metal hydroxides (Ca2+, Sr2+, and Ba2+). • Again, these substances dissociate completely in aqueous solution, strong electrolytes

  20. Titration A known concentration of base (or acid) is slowly added to a solution of acid (or base).

  21. Titration A pH meter or indicators are used to determine when the solution has reached the equivalence point, at which the stoichiometric amount of acid equals that of base.

  22. Titration of a Strong Acid with a Strong Base From the start of the titration to near the equivalence point, the pH goes up slowly.

  23. Titration of a Strong Acid with a Strong Base Just before and after the equivalence point, the pH increases rapidly.

  24. Titration of a Strong Acid with a Strong Base At the equivalence point, moles acid = moles base, and the solution contains only water and the salt from the cation of the base and the anion of the acid.

  25. Titration of a Strong Acid with a Strong Base As more base is added, the increase in pH again levels off.

  26. Neutralization Neutralization Reaction = Acid + Base  Salt + Water Salt – ionic compound containing a positive ion other than H+ and a negative ion other than OH-

  27. Buffered solutions – resists a change in its pH even when a strong acid or base is added to it - A solution is buffered in the presence of a weak acid and its conjugate base

  28. pH and pOH Calculations

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