1 / 44

Entry Task: Jan 24 th Thursday

Entry Task: Jan 24 th Thursday . Question: What distinguishes acids from bases? You have 5 minutes!. Agenda:. Sign off on Ch. 16 sec. 1-4 reading notes In-class practice HW: Acid/Base Properties ws (review from last year). Equation Sheet. I can….

essien
Download Presentation

Entry Task: Jan 24 th Thursday

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Entry Task: Jan 24th Thursday Question: What distinguishes acids from bases? You have 5 minutes!

  2. Agenda: • Sign off on Ch. 16 sec. 1-4 reading notes • In-class practice • HW: Acid/Base Properties ws(review from last year)

  3. Equation Sheet

  4. I can… • Distinguish an acid from a base by its properties. • Explain the difference theories of acid and base behavior of an Arrhenius A/B, Bronsted-Lowry A/B and Lewis A/B. • Use the concentrations of acids and bases to calculate pH and pOH.

  5. Chapter 16Acids and Bases Sections 1 through 4

  6. WarningBlack text slides are embedded notes

  7. Define Acids and Bases • Arrhenius • Acid: Substance that, when dissolved in water, increases the concentration of hydrogen ions. HCl (g) (in water) H+(aq) + Cl-(aq) • Base: Substance that, when dissolved in water, increases the concentration of hydroxide ions. NaOH (s) (in water) Na+(aq) + OH-(aq)

  8. Brønsted-Lowry Acids and Bases • Brønsted–Lowry • Acid: Proton (H+) donor • Base:Proton (H+) acceptor

  9. A Brønsted–Lowry acid… …must have a removable (acidic) proton. HCl(g) + H2O (l)  H3O+ (aq) + Cl- (aq) A Brønsted–Lowry base… …must have a pair of nonbonding electrons. NH3(g) + H2O (l)  NH4+ (aq) + OH- (aq)

  10. If it can be either… ...it is amphiprotic. HCO3− HSO4− H2O

  11. What Happens When an Acid Dissolves in Water? • Water acts as a Brønsted–Lowry base and abstracts a proton (H+) from the acid. • As a result, the conjugate base of the acid and a hydronium ion are formed.

  12. Conjugate Acids and Bases: • From the Latin word conjugare, meaning “to join together.” • Reactions between acids and bases always yield their conjugate bases and acids.

  13. H H Cl O acid base H H Why is HCl an acid? It donates its proton. Why is water a base? It accepts the proton.

  14. + H - H Cl Cl O O conjugate acid conjugate base acid base H H H H What is the conjugate acid and why? H3O+, because it’s now able to donate a proton. What is the conjugate base and why? Cl-, because it’s now able to accept a proton.

  15. O H H H N H acid base H H Why is water an acid? It donates its proton Why is NH3 a base? It accepts a proton.

  16. + H - O H O N N H H base acid conjugate acid conjugate base H H H H H H What is the conjugate acid and why? NH4+, because its now able to donate a proton. What is the conjugate base and why? OH-, because its now able to accept a proton.

  17. NH4+ + OH- NH3 + H2O What is happening here? Looks like NH4+ has lost a proton to OH-, becoming the proton donor- ACID Looks like OH- gained a proton is becomes a BASE When a acid (NH4+) donates a proton becoming NH3, it becomes conjugate base.- because it now able to accept a proton. When a base (OH-) accepts a proton it becoming H2O conjugate acid.- because it now able to donate a proton.

  18. HBr + H2O  H3O+ + Br- What is happening here? Looks like HBr has lost a proton to H2O, becoming the proton donor- ACID Looks like H2O gained a proton is becomes a BASE When a acid (HBr) donates a proton becoming Br-, it becomes conjugate base.- because it now able to accept a proton. When a base (H2O) accepts a proton it becoming H3O+ conjugate acid.- because it now able to donate a proton.

  19. Acid and Base Strength • Strong acids are completely dissociated in water. • Their conjugate bases are quite weak. • Weak acids only dissociate partially in water. • Their conjugate bases are weak bases.

  20. Graphical representation of the behavior of acids of different strengths in aqueous solution. A Strong Acid A Weak Acid

  21. Acid and Base Strength • Substances with negligible acidity do not dissociate in water. • Their conjugate bases are exceedingly strong.

  22. Acid and Base Strength In any acid-base reaction, the equilibrium will favor the reaction that moves the proton to the stronger base. HCl(aq) + H2O(l) H3O+(aq) + Cl−(aq) H2O is a much stronger base than Cl−, so the equilibrium lies so far to the right K is not measured (K>>1).

  23. HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2−(aq) Acid and Base Strength Acetate is a stronger base than H2O, so the equilibrium favors the left side (K<1).

  24. H2O(l) + H2O(l) H3O+(aq) + OH−(aq) Autoionization of Water As we have seen, water is amphoteric. In pure water, a few molecules act as bases and a few act as acids. This is referred to as autoionization.

  25. Ion-Product Constant The equilibrium expression for this process is Kc = [H3O+] [OH−] This special equilibrium constant is referred to as the ion-product constant for water, Kw. At 25°C, Kw = 1.0  10−14

  26. Kw constant Calculate the values of [H+] and [OH-] in a neutral solution at 25°C. [H+] [OH-] = (x)(x) = 1.0x 10-14 (x)2 = 1.0x 10-14 Square root both sides and x = 1.0x 10-7

  27. Kw constant If the [H+] is 1.0x 100 or 1 this means it contains only H+ ions and NO OH- ions If the [H+] is 1.0x 10-1 to 1.0x 10-6 means is contains more H+ ions than OH- ions-therefore an acidic solution

  28. Kw constant If the [OH-] is 1.0x 100 or 1 this means it contains only OH- ions and NO H+ ions If the [OH-] is 1.0x 10-1 to 1.0x 10-6 means is contains more OH- ions than H+ ions-there for a basic solution

  29. Kw constant Indicate whether each of the following solutions is neutral, acidic or basic: [H+] 2 x10-5 M This is an acidic solution [OH-] 2 x10-9 M This is an acidic solution [OH-] 1 x10-7 M This is an neutral solution

  30. Kw constant Calculate the values of [H+] in a (a) solution in which [OH-] is 0.010 M (b) a solution in which [OH-] is 2.0x10-9M. [H+] [OH-] = (x)(x) = 1.0x 10-14 [H+] = 1.0x 10-14 [H+] = 1.0x 10-14 [OH-] [0.010] [H+]= 1.0x 10-12 this is a basic solution

  31. Kw constant Calculate the values of [H+] in a (a) solution in which [OH-] is 0.010 M (b) a solution in which [OH-] is 2.0x10-9M. [H+] [OH-] = (x)(x) = 1.0x 10-14 [H+] = 1.0x 10-14 [H+] = 1.0x 10-14 [OH-] [2.0x 10-9] [H+]= 5.0x 10-6 this is a acidic solution

  32. pH pH is defined as the negative base-10 logarithm of the hydrogen ion concentration. pH = −log [H+]

  33. pH • In pure water, Kw = [H3O+] [OH−] = 1.0  10−14 • Because in pure water [H3O+] = [OH−], [H3O+] = (1.0  10−14)1/2 = 1.0  10−7

  34. pH How does the [H+] concentration affect the kinetic rate law? The rate law is first order, double the concentration of [H+], the rate doubles.

  35. pH • Therefore, in pure water, pH = −log (1.0  10−7) = 7.00 • An acid has a higher [H3O+] than pure water, so its pH is <7 • A base has a lower [H3O+] than pure water, so its pH is >7.

  36. pH These are the pH values for several common substances

  37. Calculate pH If we have a [H+] of 1.0 x10-12, what is the pH? pH = -log (1.0 x 10-12) = pH = -(-12.00) = 12 What is the pH of a solution which has [H+] of 5.0 x10-6? pH = -log (5.0 x10-6) = pH = -(-5.30) = 5.30

  38. Calculate pH If we have a [H+] of 3.8 x10-4, what is the pH? pH = -log (3.8 x10-4) = pH = -(-3.42) = 3.42 What is the pH of a solution which has [H+] of 5.3 x10-9? pH = -log (5.3 x10-9) = pH = -(-8.28) = 8.28

  39. Calculate concentration from pH Calculate the amount of [H+] with a solution with a pH of 3.76 3.76 = -log [H+] Get the negative to the other side -3.76 = log [H+] AntiLog both sides [H+] = -3.76 [H+]= 1.7 x10-4

  40. Calculate concentration from pH Calculate the amount of [H+] with a solution with a pH of 9.18 9.18 = -log [H+] Get the negative to the other side -9.18 = log [H+] AntiLog both sides [H+] = -9.18 [H+]= 6.6 x10-10

  41. Other “p” Scales • The “p” in pH tells us to take the negative log of the quantity (in this case, hydrogen ions). • Some similar examples are • pOH−log [OH−] • pKw−log Kw

  42. Watch This! Because [H3O+] [OH−] = Kw = 1.0  10−14, we know that −log [H3O+] + −log [OH−] = −log Kw = 14.00 or, in other words, pH + pOH = pKw = 14.00

  43. 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

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

More Related