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1 Slide 1 / 33 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website:

2 Slide 2 / 33 AP Chemistry Unit 3: Presentation D Acids and Bases

3 Slide 3 / 33 Acid/Base Reactions CaCO 3(s) + 2H + (aq) --> H 2 O (l) + CO 2(g) + Ca 2+ (aq) Caves are formed by the acid/base reaction of limestone with acid which causes the limestone rock to dissolve away.

4 Slide 4 / 33 Acid and Base Definitions The most widely used definition of acids and bases in the Bronsted- Lowry definition. ACID H + Donor BASE H + acceptor NH 4 + (aq) + H 2 O (l) --> NH 3(g) + H 3 O + (aq) Acid: H + Donor Base: H + Acceptor

5 Slide 5 / 33 Conjugate Acids and Bases After an acid donates an H+ ion, the resulting species can always behave as a base and grab the H+ back again. NH 4 + (aq) + H 2 O <--> NH 3(g) + H 3 O + (aq) Base: H + Acceptor Acid: H + Donor Therefore, NH 3 acts as the conjugate base of NH 4 + and H 3 O + acts as the conjugate acid of H 2 O. NH 4 + (aq) + H 2 O (l) <--> NH 3(g) + H 3 O + (aq)

6 Slide 6 / 33 Conjugate Acids and Bases Predicting the formula of a conjugate acid or base involves writing the formula of the species produced after the donation or acceptance of an H+ ion. CN - (aq) --> HCN (aq) base Conj. acid HCO 3 - (aq) --> CO 3 2- (aq) acid Conj. base CH 3 NH 2(aq) --> CH 3 NH 3 + (aq) base Conj. acid CH 3 COOH (aq) --> CH 3 COO - (aq) acid Conj. base

7 Slide 7 / 33 Amphoteric Molecules Amphoteric molecules can behave as either acids or bases depending on their environment. Water is a classic example H 2 O donates H + accepts H + OH - H 3O + Conj. base Conj. acid Whether water acts as an acid or base will depend on the relative "strength" of other acids or bases it is reacted with.

8 Slide 8 / 33 Amphoteric Molecules Common amphoteric molecules are the conjugate bases of diprotic or polyprotic acids H 2 C 2 O 4(aq) HC 2 O 4 - (aq) C 2 O 4 2- (aq) Acid Amphoteric Base H 3 PO 4(aq) H 2 PO 4 - (aq) HPO 4 2- (aq) PO 4 3- (aq) Acid Amphoteric Amphoteric Base

9 Slide 9 / 33 1 Which of the following is NOT an acid/base reaction? A HCN (aq) + H 2 O (l) --> CN - (aq) + H 3 O + (aq) B NH 3(aq) + HC 2 H 3 O 2(aq) --> NH 4 + (aq) + C 2 H 3 O 2 - (aq) C H + (aq) + H 2 O (l) --> H 3 O + (aq) D Pb 2+ (aq) + 2I - (aq) --> PbI 2(s) E All are acid/base reactions

10 Slide 9 (Answer) / 33 1 Which of the following is NOT an acid/base reaction? A HCN (aq) + H 2 O (l) --> CN - (aq) + H 3 O + (aq) B NH 3(aq) + HC 2 H 3 O 2(aq) --> NH 4 + (aq) + C 2 H 3 O 2 - (aq) C H + (aq) + H 2 O (l) --> H 3 O + (aq) D Pb 2+ (aq) + 2I - (aq) --> PbI 2(s) Answer E All are acid/base reactions D [This object is a pull tab]

11 Slide 10 / 33 2 In which of the following reactions does the underlined substance behave as an acid? A I only B II only I. CH 3 NH 2(g) + H 2 O (l) --> CH 3 NH 3 + (aq) + OH - (aq) II. HCOOH (aq) + NH 2 - (aq) --> HCOO - (aq) + NH 3(aq) III. HClO (aq) + OH- (aq) --> ClO - (aq) + H 2 O (l) C III only D II and III only E I, II, and III

12 Slide 10 (Answer) / 33 2 In which of the following reactions does the underlined substance behave as an acid? A I only B II only I. CH 3 NH 2(g) + H 2 O (l) --> CH 3 NH 3 + (aq) + OH - (aq) II. HCOOH (aq) + NH 2 - (aq) --> HCOO - (aq) + NH 3(aq) III. HClO (aq) + OH- (aq) --> ClO - (aq) + H 2 O (l) C III only D II and III only Answer D E I, II, and III [This object is a pull tab]

13 Slide 11 / 33 3 What would be the expected products of the following reaction... H 2 PO 4 - (aq) + OH - (aq) --> A H 3 PO 4(aq) + H 2 O (l) B H 2 PO 4 2- (aq) + H 2 O (l) C HPO 4 - (aq) + H 3 O + (aq) D HPO 4 2- (aq) + H 2 O (l) E None of these

14 Slide 11 (Answer) / 33 3 What would be the expected products of the following reaction... H 2 PO 4 - (aq) + OH - (aq) --> A H 3 PO 4(aq) + H 2 O (l) B H 2 PO 4 2- (aq) + H 2 O (l) Answer C HPO 4 - (aq) + H 3 O + (aq) D D HPO 4 2- (aq) + H 2 O (l) E None of these [This object is a pull tab]

15 Slide 12 / 33 4 Which of the following is the conjugate acid of the chlorite ion (ClO 2 -)? A HClO 2 B HClO 2 + C HClO D HClO 3 E HClO 2 -

16 Slide 12 (Answer) / 33 4 Which of the following is the conjugate acid of the chlorite ion (ClO 2 -)? A HClO 2 B HClO 2 + C HClO Answer A D HClO 3 E HClO 2 - [This object is a pull tab]

17 Slide 13 / 33 5 Which of the following has the acid paired with it's appropriate conjugate base? A I only B II only I. HPO 4 2- (aq) /PO 4 2- (aq) II. HBrO 2(aq) /BrO - (aq) III. H 2 CrO 4(aq) /HCrO 4 - (aq) C III only D I and III only E I and II only

18 Slide 13 (Answer) / 33 5 Which of the following has the acid paired with it's appropriate conjugate base? A I only B II only C III only D I and III only E I and II only Answer I. HPO 2-4 (aq) /PO 2-4 (aq) II. HBrO 2(aq) /BrO - (aq) - III. H 2 CrO 4(aq) /HCrO 4 (aq) C [This object is a pull tab]

19 Slide 14 / 33 6 Which of the following would be amphoteric? A CO 3 2- (aq) B HC 2 H 3 O 2(aq) C HC 2 O 4 - (aq) D F - (aq) E H 3 O + (aq)

20 Slide 14 (Answer) / 33 6 Which of the following would be amphoteric? A CO 3 2- (aq) B HC 2 H 3 O 2(aq) C HC 2 O 4 - (aq) Answer C D F - (aq) E H 3 O + (aq) [This object is a pull tab]

21 Slide 15 / 33 Strong Acids Strong acids dissociate 100% in aqueous solutions thereby donating ALL of their H+ ions. Therefore, much like a soluble ionic compound, any strong acid must be written as being broken up into it's ions. Strong Acid HCl (aq) Written as... H + (aq) + Cl - (aq) HNO 3(aq) H + (aq) + NO 3 - (aq) H 2 SO 4(aq) HClO 4(aq) HBr (aq) HI (aq) 2H + 2- (aq) + SO 4 (aq) H + - (aq) + ClO 4 (aq) H + (aq) + Br - (aq) H + (aq) + I - (aq)

22 Slide 16 / 33 Strong Acids Conjugate bases of strong acids are not able to accept H+ ions back and therefore do not participate in acid/base reactions. H + (aq) + NO 3 - (aq) + NH 3(aq) --> NH 4 + (aq) H + (aq) + NH 3(aq) --> NH 4 + (aq) H + (aq) + Br - (aq) + ClO - (aq) --> HClO (aq) H + (aq) + ClO - (aq) --> HClO (aq)

23 Slide 17 / 33 Writing Acid/Base Reactions First write the correct formulas for all species involved, breaking compounds into ions if soluble ionics or strong acids. Example: Aqueous solutions of methlyamine (CH3NH2) and hydroiodic acid are mixed. CH 3 NH 2(aq) + H + (aq) + I - (aq) --> Predict products based on acid/base principles. CH 3 NH 2(aq) + H + (aq) + I - (aq) --> CH 3 NH 3 + (aq) CH 3 NH 2(aq) + H + (aq) --> CH 3 NH 3 + (aq)

24 Slide 18 / 33 7 Which of the following species would be an extremely weak base? A Br - B F - - C NO 2 D ClO - 3 E NH 3

25 Slide 18 (Answer) / 33 7 Which of the following species would be an extremely weak base? A Br - B F - - C NO 2 D ClO - 3 E NH 3 Answer A [This object is a pull tab]

26 Slide 19 / 33 8 Why are strong acids written as separate ions? A Strong acids are dangerous B Strong acids have strong conjugate bases C Strong acids do not have conjugate bases D Strong acids donate all of their H+ ions E None of these

27 Slide 19 (Answer) / 33 8 Why are strong acids written as separate ions? A Strong acids are dangerous B Strong acids have strong conjugate bases Answer C Strong acids do not have conjugate bases D Strong acids donate all of their H+ ions D E None of these [This object is a pull tab]

28 Slide 20 / 33 9 Which of the following is NOT a strong acid? A HNO 3 B HF C HBr D HClO 4 E H 2 SO 4

29 Slide 20 (Answer) / 33 9 Which of the following is NOT a strong acid? A HNO 3 B HF C HBr D HClO 4 Answer B E H 2 SO 4 [This object is a pull tab]

30 Slide 21 / Which of the following best represents the balanced equation for the acid/base reaction of aqueous potassium hydroxide and chromic acid (H 2 CrO 4 )? A OH - + H 2 CrO 4 H 2 O + CrO 4 2- B 2K + + H 2 CrO 4 2H + + K 2 CrO 4 C 2OH - + H 2 CrO 4 2H 2 O + CrO 4 2- D 2K + + H 2 CrO 4 2KH + CrO 4 2- E None of these

31 Slide 21 (Answer) / Which of the following best represents the balanced equation for the acid/base reaction of aqueous potassium hydroxide and chromic acid (H 2 CrO 4 )? A OH - + H 2 CrO 4 H 2 O + CrO 4 2- B 2K + + H 2 CrO 4 2H + + K 2 CrO 4 Answer C 2OH - + H 2 CrO 4 2H 2 O + CrO 4 2- C D 2K + + H 2 CrO 4 2KH + CrO 4 2- E None of these [This object is a pull tab]

32 Slide 22 / Which of the following best represents the balanced equation for the acid/base reaction if solid strontium hydroxide is added to a solution of acetic acid (HC 2 H 3 O 2 )? - A Sr(OH) 2 + 2HC 2 H 3 O 2 2C 2 H 3 O 2 + Sr H 2 O B 2OH - + 2HC 2 H 3 O 2 2C 2 H 3 O H 2 O - C Sr(OH) 2 + 2C 2 H 3 O 2 Sr(C 2 H 3 O 2 ) 2 + 2OH - - D Sr(OH) 2 + HC 2 H 3 O 2 C 2 H 3 O 2 + Sr 2+ + H 2 O E None of these

33 Slide 22 (Answer) / Which of the following best represents the balanced equation for the acid/base reaction if solid strontium hydroxide is added to a solution of acetic acid (HC 2 H 3 O 2 )? A Sr(OH) 2 + 2HC 2 H 3 O 2 2C 2 H 3 O Sr H 2 O B 2OH - + 2HC 2 H 3 O 2 2C 2 H 3 O H 2 O A - C Sr(OH) 2 + 2C 2 H 3 O 2 Sr(C 2 H 3 O 2 ) 2 + 2OH - - D Sr(OH) 2 + HC 2 H 3 O 2 C 2 H 3 O 2 + Sr 2+ + H 2 O E None of these Answer [This object is a pull tab]

34 Slide 23 / Which of the following best represents the balanced equation for the acid/base reaction when solutions of sodium hypobromite (NaBrO) and sulfurous acid (H 2 SO 3 ) are mixed? A 2Na + + SO 3 2- Na 2 SO 3 B 2OBr - + H 2 SO 3 2HBr + SO 4 2- C 2OBr - + H 2 SO 3 2OH - + Br 2 SO 3 D 2OBr - + H 2 SO 3 2HOBr + SO 3 2- E None of these

35 Slide 23 (Answer) / Which of the following best represents the balanced equation for the acid/base reaction when solutions of sodium hypobromite (NaBrO) and sulfurous acid (H 2 SO 3 ) are mixed? A 2Na + + SO 3 2- Na 2 SO 3 B 2OBr - + H 2 SO 3 2HBr + SO 4 2- Answer C 2OBr - + H 2 SO 3 2OH - + Br 2 SO 3 D D 2OBr - + H 2 SO 3 2HOBr + SO 3 2- E None of these [This object is a pull tab]

36 Slide 24 / 33 Acid/Base Stoichiometry Normal stoichiometrical calculations are routinely carried out with acid/ base reactions however there are some specific applications that will be addressed here. Application Titration Molar Mass Determination Purpose Determine (M) of acid or base by reacting it with a known quantity of acid or base Determine molar mass (g/mol) of acid or base by reacting it with a known quantity of acid or base.

37 Slide 25 / 33 Titrations In a titration, a known(standardized) solution of acid or base is carefully added to the unknown concentration of acid or base until the reaction is complete. standardized acid or base solution of known M (titrant) unknown concentration of acid or base solution (analyte) By measuring the moles of titrant added, the moles of the analyte can be determined and hence the concentration (M).

38 Slide 26 / 33 Titrations Example: What is the concentration of a 10 ml acetic acid solution if 34.1 ml of 0.2 M KOH was needed to titrate it? Write Reaction OH - (aq) + HC 2 H 3 O 2(aq) --> C 2 H 3 O 2 - (aq) + H 2 O (l) Determine moles of titrant reacted and moles of analyte present L x 0.2 n OH- x 1 mol HC 2 H 3 O 2 = mol 1 L 1 mol OH- Find Molarity mol/0.010 L = M

39 Slide 27 / 33 Using Titrations to Find Molar Mass The identity of an acid can be discerned if the molar mass of the acid is known. The molar mass is determined by titrating a known mass of an acid dissolved in water with a standardized base. Molar Mass = grams/mol

40 Slide 28 / 33 Using Titrations to Find Molar Mass Example: If 3.1 grams of an acid are dissolved up with water to make a 25 ml solution it was determined that 45.9 ml of a 2.5 M NaOH standardized solution is needed to titrate the acid. What is the molar mass of the acid? unknown acid HA (aq) + OH - (aq) --> H 2 O (aq) + A - (aq) L x 2.5 n OH- x 1 n HA = mol HA 1 L 1 n OH- Molar Mass = g/mol g/ mol = 27 g/mol (HCN)

41 Slide 29 / How many ml of M KOH would be needed to completely titrate 100. ml of M HCl?

42 Slide 29 (Answer) / How many ml of M KOH would be needed to completely titrate 100. ml of M HCl? Answer 64.5 ml [This object is a pull tab]

43 Slide 30 / How many ml of M Ca(OH) 2 would be needed to titrate 120. ml of M nitrous acid (HNO 2 )?

44 Slide 30 (Answer) / How many ml of M Ca(OH) 2 would be needed to titrate 120. ml of M nitrous acid (HNO 2 )? Answer 388 ml [This object is a pull tab]

45 Slide 31 / What is the molarity of a 50.0 ml solution of acetic acid (CH 3 COOH) if it took 5.0 ml of 1 M NaOH to fully titrate it?

46 Slide 31 (Answer) / What is the molarity of a 50.0 ml solution of acetic acid (CH 3 COOH) if it took 5.0 ml of 1 M NaOH to fully titrate it? Answer 0.10 M [This object is a pull tab]

47 Slide 32 / What is the molar mass of a monoprotic acid if after gram sample of it is dissolved in water, 45.0 ml of M KOH is needed to titrate it completely?

48 Slide 32 (Answer) / What is the molar mass of a monoprotic acid if after gram sample of it is dissolved in water, 45.0 ml of M KOH is needed to titrate it completely? Answer 31.9 g/mol [This object is a pull tab]

49 Slide 33 / Which of the following would be the identity of an acid if after grams of it are dissolved in water, 6.89 ml of 1.1 M NaOH was needed to titrate it? A HBrO B HCN C HClO D HI E HC 3 H 6 O 3

50 Slide 33 (Answer) / Which of the following would be the identity of an acid if after grams of it are dissolved in water, 6.89 ml of 1.1 M NaOH was needed to titrate it? A HBrO B HCN C HClO D HI Answer C E HC 3 H 6 O 3 [This object is a pull tab]