Acids, Bases and ph Chapter 19

Transcription

1 Acids, Bases and ph Chapter 19

2 Compounds That Become Acids When Dissolved in Water General Formula: HX H + X - monatomic or polyatomic anion

3 Naming Acids (p. 250) Binary acids Hydro ic Acid HCl: Hydrochloric acid HBr: Hydrobromic acid HS: Hydrosulfuric acid Oxyacids ite becomes ous Acid from chlorite: HClO 2 = chlorous acid Acid from phosphite: H 3 PO 3 = phosphorous acid ate becomes ic Acid from sulfate: H 2 SO 4 = sulfuric acid

4 Compounds That Become Acids When Dissolved in Water Your turn: HBr HNO 2 HNO 3

5 Compounds That Become Acids When Dissolved in Water Your turn: HBr hydrobromic acid HNO 2 nitrous acid HNO 3 nitric acid

6 Practice Name or write formulas for the following acids: 1. Phosphoric Acid 5. HClO 4 2. Hydrochloric Acid 6. HI 3. Chlorous Acid 7. H 2 S 4. Sulfurous Acid 8. HC 2 H 3 O 2 9. Write the balanced formula, total ionic and net ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide

7 Practice Name or write formulas for the following acids: 1. phosphoric acid H 3 PO 4 2. hydrochloric acid HCl 3. chlorous Acid HClO 2 4. sulfurous Acid H 2 SO 3 5. HClO 4 perchloric acid 6. HI hydroiodic acid 7. H 2 S hydrosulfuric acid 8. HC 2 H 3 O 2 acetic acid

8 Practice 9. Write the balanced formula, total ionic and net ionic equations for the acid base neutralization reaction that occurs when aqueous sulfuric acid is mixed with aqueous potassium hydroxide (put answer on front whiteboard)

9 Properties of Acids and Bases Acids Bases Taste sour Taste bitter Feel wet Feel slippery Turn litmus RED Turn litmus BLUE Conduct electricity Conduct electricity React with most metals Do NOT react with most metals Contain more H + than OH - Contain more OH - than H + ph between 0 and 7 ph between 7 and 14 strong acid + strong base salt + H 2 O

10 Arrhenius acids and bases Acid: compound containing H that ionizes to yield H + in solution HCl (g) H + (aq) + Cl - (aq) HCl (g) + H 2 O (l) H H 3 O + (aq) + Cl - 2 O (aq) Base: compound containing OH that ionizes to NaOH (s) Na + (aq) + OH - (aq) yield OH - in solution *Note: Every Arrhenius acid/base is also a Brønsted-Lowry acid/base. H 2 O

11 Autoionization of Water H 2 O + H 2 O H 3 O + + OH - In pure water : [H 3 O + ] = 1.0 x 10-7 M AND [OH - ] = 1.0 x 10-7 M If we add acid [H 3 O + ] increases and [OH - ] decreases. [H 3 O + ] = 1.0 x 10-4 M [OH - ] = 1.0 x M If we add base, the reverse is true: [H 3 O + ] = 1.0 x M [OH - ] = 1.0 x 10-4 M What is the product of [H 3 O + ] x [OH - ] in each case?

12 The ph Scale ph = - log [H + ] = - log (1.0 x 10-7 ) = -(-7) = 7 Pure Water poh = - log [OH - ] = - log (1.0 x 10-7 ) = -(-7) = 7 basis of neutral ph 7:[H + ] = [OH - ]

13 Concentration, ph and poh (for strong acids and bases) Concentration is given in terms of molarity (M) Concentration of H + = [H + ] = moles H + L solution = M In scientific notation: [H + ] = 1.00 x 10-2 M Find ph: ph = -log[1.00 x 10-2 M] ph = 2 Find poh: ph + poh = 14 poh = 12 Find [OH-]: [OH-] = 10 -poh = [OH - ] = 1.00 x M

14 Converting between Concentration and ph 10 -poh [H + ] -log[h + ] ph poh [OH - ] 14-pH 1.00 x 10-4 M x M [OH - ] -log[oh - ] 14-pOH 10 -ph poh ph [H + ] 1.00 x M x 10-3 M

15 Practice ph + poh = 14; ph = -log[h + ]; poh = -log[oh - ] When ph = 2 [H + ] = M poh = [OH - ] = M When poh = 8 [OH - ] = M ph = [H + ] = M [H + ] = 1.0 x 10-3 M What is the [OH - ]?

16 More Practice (HW) 1. What is the ph of a solution with a [H + ] of 10-8 M? 2. What is the poh of a solution with a [OH - ] of M? 3. What is the ph of a solution with a [OH - ] of 10-2 M? 4. What is the poh of a solution with a [H + ] = 10-5 M? 5. Which is more acidic, a solution with a ph of 6 or one with a ph of 9? 6. Which is more basic, a solution with a poh of 7 or one with a poh of 12? 7. Which is more acidic, a solution with a ph of 5 or one with a poh of 10? 8. Which is more basic, a solution with a ph of 8 or one with a poh of 12?

17 More Practice 1. What is the ph of a solution with a [H + ] of 10-8 M? 8 2. What is the poh of a solution with a [OH - ] of M? What is the ph of a solution with a [OH - ] of 10-2 M? What is the poh of a solution with a [H + ] = 10-5 M? 9 5. Which is more acidic, a solution with a ph of 6 or one with a ph of 9? ph of 6 6. Which is more basic, a solution with a poh of 7 or one with a poh of 12? poh of 7 7. Which is more acidic, a solution with a ph of 5 or one with a poh of 10? poh of Which is more basic, a solution with a ph of 8 or one with a poh of 12? ph of 8

18 More Practice 9. Stomach contents can have a ph of 3. Are stomach contents acidic, basic or neutral? 10. Pure water has a poh of 7. Is pure water acidic, basic or neutral? 11. Normal rain has a ph of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic? 12. Acid precipitation is often a problem in industrialized areas. What might you expect the ph of acid rain to be?

19 More Practice 9. Stomach contents can have a ph of 3. Are stomach contents acidic, basic or neutral? acidic 10. Pure water has a poh of 7. Is pure water acidic, basic or neutral? neutral 11. Normal rain has a ph of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic? slightly acidic 12. Acid precipitation is often a problem in industrialized areas. What might you expect the ph of acid rain to be? < 6

20 Warm up 1. Write formulas for the following acids: a) hydroiodic acid b) chlorous acid c) chloric acid d) perchloric acid (Honors) e) hypochlorous acid (Honors) f) phosphoric acid g) phosphorous acid

21 Warm up 1. Write formulas for the following acids: a) hydroiodic acid HI b) chlorous acid HClO 2 c) chloric acid HClO 3 d) perchloric acid HClO 4 (Honors) e) hypochlorous acid HClO (Honors) f) phosphoric acid H 3 PO 4 g) phosphorous acid H 3 PO 3 (Honors)

22 Warmup What is the ph of a solution of nitric acid (strong acid) that has a concentration of 10-4 M? What is its poh? Concentration of OH -?

23 Warmup What is the ph of a solution of nitric acid (strong acid) that has a concentration of 10-4 M? 4 What is its poh? 10 Concentration of OH -? M

24 Acid-base Indicators Acid-base indicator = a weak acid or base that undergoes dissociation in a known ph range. In this range, the acid (base) is a different color from its conjugate base (or acid). Universal indicator (UI) = a mixture of indicators that shows a range of colors over a wide range of ph values

25 Intro to ph Serial Dilution Lab Overview: you will create a ph scale (1 to 14) by serial dilutions, then test acid-base indicators. Serial Dilutions 1 drop 1 M HCl + 9 drops dh 2 O = 10X dilution i.e. 1M 0.1 M, which is ph = 1 1 drop 0.1 M HCl + 9 drops dh 2 O = 10X dilution i.e. 0.1M 0.01 M 10-2 M, which is ph = 2

26 Intro to ph Serial Dilution Lab Safety: apron and goggles Complete the pre-lab questions on the first page before you go into lab Work on your own

27 Intro to ph Serial Dilution Lab Begin with UI, then choose at least two other acid-base indicators to test. Use dh 2 O dropper bottle for the 9 drops of water per well. Be sure to rinse pipet with dh 2 O between dilutions. Collect this dh 2 O into a beaker from the carboys by the windows. Rinse and dry wellplates/spot plates between runs (use dh 2 O).

28 Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) 2009, Prentice-Hall, Inc.

29 Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) Na + (aq) + Cl - (aq) + H 2 O (l) 2009, Prentice-Hall, Inc.

30 Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) Na + (aq) + Cl - (aq) + H 2 O (l) H + (aq) + OH - (aq) H 2 O (l) 2009, Prentice-Hall, Inc.

31 Titration Titration is an analytical technique in which one can calculate the concentration of a solute in a solution. 2009, Prentice-Hall, Inc.

32 Titration = A method of volumetric analysis in which a volume of one reagent is added to a known volume of another reagent slowly from a buret until an end point is reached. If one of the solutions has a known concentration, the concentration of the other can be calculated, via stoichiometry. 2009, Prentice-Hall, Inc.

33 Titration Standard solution = reagent solution of known concentration Titrant = reagent solution of unknown concentration Equivalence point = the point at which stoichiometrically equivalent quantities are brought together End point = color change (v. close to equivalence point) 2009, Prentice-Hall, Inc.

34 Change in appearance of a solution containing phenolphthalein as base indicator 2009, Prentice-Hall, Inc.

35 Titration 2009, Prentice-Hall, Inc.

36 Example Titration Predict the number of ml of ~0.10 M NaOH needed to neutralize 10.0 ml of 0.25 M HCl. We want to know the exact molarity of the NaOH solution. 2009, Prentice-Hall, Inc.

37 Titration Practice Problems Remember: Moles are central! 1. In the titration of 35 ml of liquid drain cleaner containing NaOH, 50. ml of 0.40 M HCl must be added to reach the equivalence point. What is the molarity of the base in the cleaner? (0.57 M) 2009, Prentice-Hall, Inc.

38 Titration Practice Problems Remember: Moles are central! 2. A 20.0 ml sample of an HCl solution is titrated with 27.4 ml of a standard solution of Ba(OH) 2. The concentration of the standard is M. What is the molarity of the HCl? ( M) 2009, Prentice-Hall, Inc.

39 Strength of Acids and Bases Strong acid or base ionizes/dissociates completely in water [H + ] or [OH - ] = conc. of acid or base. e.g. HCl, NaOH. 5 units of acid 5 out of 5 dissociated H + Cl - H + Cl - H + Cl - H + Cl - H + Cl - Weak acid or base ionizes/dissociates only partially in water [H + ] or [OH - ] < conc. of acid or base. e.g. HC 2 H 3 O 2, NH 3 5 units only 1 out of 5 dissociated HC 2 H 3 O 2 HC 2 H 3 O 2 HC 2 H 3 O 2 HC 2 H 3 O 2 H + C 2 H 3 O 2 -

40 Practice The diagrams below represent aqueous solutions of three acids (HX, HY, and HZ) with water molecules omitted for clarity. Rank them from strongest to weakest. 2009, Prentice-Hall, Inc.

41 Strengths of Acids and Bases Strong concentrated Weak dilute A concentrated weak acid (or base) may have the same ph as a dilute strong acid (or base).

42 Strong vs. Weak Demo Strong acid: HCl + H 2 O Cl - + H 3 O x 10-2 M? M ph =? Strong base: NaOH + H 2 O Na + + OH x 10-2 M? M ph =? Weak acid: HC 2 H 3 O 2 + H 2 O C 2 H 3 O 2- + H 3 O x 10-2 M? M ph =? Weak base: NH 3 + H 2 O NH 4+ + OH x 10-2 M? M ph =?

43 Strong and Dilute vs. Weak and Concentrated Acids: Strong HCl Weak HC 2 H 3 O 2 Weak HC 2 H 3 O 2 Dilute Dilute Conc 100 x 0.01 M 0.01 M 1M ph = ph = ph = Bases: Strong NaOH Weak NH 3 Weak NH 3 Dilute Dilute Conc 100 x 0.01M 0.10 M 1M ph = ph = ph =

44 Warmup Compare strong acids with weak acids. Use concentration, extent of ionization, and ph in your answer.

45 Warmup Compare strong acids with weak acids. Use concentration, extent of ionization, and ph in your answer. Strong acids ionize completely in water, so the concentration of H + is the same as the compound itself. A weak acid of equal concentration (molarity) will have a lower concentration of H +, and thus a higher ph.

46 What do you think? Are the following acidic, basic or neutral? Table salt Vinegar Rubbing alcohol Drain cleaner Applesauce Blood Window Cleaner Distilled water Lemon juice Soap What is the difference between a strong acid and a concentrated acid? A weak acid and a dilute acid?

47 Brønsted-Lowry Acids and Bases (1923) Acid: H + (proton) donor Base: H + (proton) acceptor HCl + H 2 O H 3 O + + Cl - acid base conjugate conjugate acid base

48 Brønsted-Lowry Acids and Bases (1923) NH 3 + H 2 O D NH 4+ + OH - ammonia water ammonium ionhydroxide ion (B-L base) (B-L acid) (B-L acid) (B-L base) base acid conjugate acid conjugate base

49 Conjugate Acid-Base Pairs Conjugate acid = species produced when a base accepts a hydrogen ion from an acid Conjugate base = species that results when an acid donates a hydrogen ion to a base

50 Identify the conjugate acid-base pairs: HClO + H 2 O D ClO - + H 3 O + HS - + H 2 O D H 2 S + OH - HPO H 2 O D H 2 PO OH - HPO H 2 O D PO H 3 O + An amphoteric compound is able to act as either an acid or a base. Which compounds in the above equations are amphoteric?