Name: Per: Date: Unit 11 - Acids, Bases and Salts Chemistry Accelerated Chemistry I Define each of the following: 1. Acidic hydrogens 2. Binary acids 3. Oxyacids 4. Carboxylic acid 5. Amines Name the following acids and bases. 6. HNO 3 10. H 3 PO 3 7. HClO 11. KOH 8. H 2 SO 4 12. H 2 CO 3 9. HC 2 H 3 O 2 13. CH 3 NH 2 Acid and Base Definitions 1. Identify each of the following as an acid or a base and write a chemical equation showing how it is an acid or a base according to the Arrhenius definition. The first one is done for you. a. HNO 3 (aq) acid, HNO 3 (aq) H + (aq) + NO 3 (aq) b. KOH(aq) c. HC 2 H 3 O 2 (aq) d. Sr(OH) 2 2. Identify each of the following as an acid or a base and write a chemical equation showing how it is an acid or a base according to the Arrhenius definition. a. NaOH(aq) b. HBr(aq) c. Sr(OH) 2 (aq) d. H 2 SO 4 (aq) 3. For each of the following, identify the Bronsted-acid, the Bronsted-Lowry base, the conjugate acid, and the conjugate base. a. HBr(aq) + H 2 O(l) H 3 O + (aq) + Br - (aq) Unit 11 Student Handout 1
b. NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) c. HNO 3 (aq) + H 2 O(l) H 3 O + (aq) + NO 3 - (aq) d. C 5 H 5 N(aq) + H 2 O(l) C 5 H 5 NH + (aq) + OH - (aq) 4. Which of the following are conjugate acid-base pairs? a. NH 3, NH 4 + b. HCl, HBr c. C 2 H 3 O 2 -, HC 2 H 3 O 2 d. HCO 3 -, NO 3-5. Which of the following are conjugate acid-base pairs? a. HI, I - b. HCHO 2, SO 4 2- c. PO 4 3-, HPO 4 2- d. CO 3 2-, HCl 6. Write the dissociation equation for each of the following acids or bases in water. Identify the conjugate acid/base pairs. The first one is done for you: a. HI(aq) + H 2 O(l) H 3 O + (aq) + I - (aq) Acid base conj acid conj base b. CH 3 NH 2 c. CO 3 2- d. H 2 CO 3 7. Write the dissociation equation for each of the following acids or bases in aqueous solution. Identify the conjugate acid/base pairs. a. HCl b. H 2 SO 3 c. HClO d. HCHO 2 e. HF 8. Write the formula for the conjugate acid of each of the following bases. a. CH 3 NH 2 b. C 5 H 5 N Unit 11 Student Handout 2
c. Cl - d. F - Strong Acids and Strong Bases REVIEW!! Strong Acids StrongBases Hydrochloric, HCl All Alkali metal hydroxides LiOH, KOH, NaOH, etc. Hydrobromic, HBr Ca(OH) 2 Hydroiodic, HI Ba(OH) 2 Perchloric, HClO 4 Sr(OH) 2 Chloric, HClO 3 Sulfuric, H 2 SO 4 Nitric, HNO 3 * If an acid or base is not listed in the above list it can be considered weak. * Keep in mind that conjugate acids/bases of STRONG acids/bases are considered WEAK. * Keep in mind that conjugate acids/bases of WEAK acids/bases are considered STRONG. Strong and Weak Acids and Bases 9. Classify each of the following acids as strong or weak. Write its conjugate base and classify it as weak or strong. The first one is done for you: a. HCHO 2 weak acid CHO 2 - - strong base b. HCl c. HNO 3 d. H 2 CO 3 e. HC 2 H 3 O 2 f. H 3 PO 3 Acide/Base Equilibria: K a, K b, K w 10. Butylamine (C 4 H 9 NH 2 ) is a weak base. If the initial concentration of butylamine is 0.230 M and the equilibrium concentration of hydroxide ion is 8.6 x 10 6 M, calculate the K b for butylamine. Answ: 3.2x10-10 Unit 11 Student Handout 3
11. If 0.690 mol of a weak acid is dissolved in water to a total volume of 0.75 L. At equilibrium the concentration of hydronium ion is 0.0024 M, calculate the K a for this acid. Answ: 6.3x10-6 12. Phenol (C 6 H 5 OH), commonly called carbolic acid, is a weak organic acid (K a = 1.3 x 10-10 ). First, write the dissociation equation. If you dissolve 0.195 g of the acid in enough water to make 125 ml of solution, what is the equilibrium hydronium ion concentration? What is the ph of the solution? Answ: [H 3 O + ]=1.50x10-6 M, ph = 5.83 13. The weak base methylamine, CH 3 NH 2, has K b = 4.2x10-4. First, write the dissociation equation. Calculate the equilibrium hydroxide ion concentration in a 0.25 M solution of the base. What are the ph and poh of the solution? Answ: [OH - ]=1.0x10-2 M, ph = 2 14. What is the hydronium ion concentration in 0.1 M ammonia if hydroxide ion concentration = 1.26 x 10 3 M? Is ammonia acidic, basic, or neutral? Answ: [H 3 O + ]=7.94x10-12 M, ph = 11, basic Unit 11 Student Handout 4
15. What is the hydroxide ion concentration in butter if hydronium ion concentration = 6.00 x 10 7 M? Is butter acidic, basic, or neutral? Answ: [OH - ]=1.67x10-8 M, ph = 6.22, slightly acidic 16. During the course of the day, human saliva varies between acidic and basic. What is the hydronium ion concentration in saliva if hydroxide ion concentration = 3.16 x 10 8 M? Is this sample of saliva acidic, basic, or neutral? Answ: [H 3 O + ]=3.16x10-7 M, ph = 6.50, slightly acidic 17. Determine [H 3 O + ] in each of the following acid solutions. For weak acids, give what [H 3 O + ] is less than. The first one is done for you. a. 2.5 M HI - [H 3 O + ] is 2.5 M b. 1.2 M HClO 2 - [H 3 O + ] is less than 1.2 M c. 0.25 M HClO 3 d. 2.25 M HNO 2 18. Classify each of the following bases as strong or weak. a. C 5 H 5 N b. NaOH c. Ba(OH) 2 d. CO 3 2-19. Determine [OH - ] in each of the following base solutions. For weak bases, give what [OH - ] is less than. a. 0.88 M NaOH b. 0.88 M NH 3 c. 0.88 M Sr(OH) 2 Unit 11 Student Handout 5
d. 1.55 M KOH ph and poh Calcualtions 20. Calculate [OH - ] given [H 3 O + ] in each of the following aqueous solutions and classify the solution as acidic or basic. a. [H 3 O + ] = 1.5 x 10-9 M b. [H 3 O + ] = 9.3 x 10-9 M c. [H 3 O + ] = 2.2 x 10-6 M d. [H 3 O + ] = 7.4 x 10-4 M 21. Calculate the ph of each of the following solutions. a. [H 3 O + ] = 1.7 x 10-8 M b. [H 3 O + ] = 1.0 x 10-7 M c. [H 3 O + ] = 2.2 x 10-6 M d. [H 3 O + ] = 7.4 x 10-4 M 22. Calculate [H 3 O + ] for each of the following solutions. a. ph = 8.55 b. ph = 11.23 c. ph = 2.87 d. ph = 1.22 23. Calculate [OH - ] for each of the following solutions. a. ph = 4.25 b. ph = 12.53 c. ph = 1.50 d. ph = 8.25 24. Calculate the ph of each of the following solutions: a. 0.0155M HBr b. 1.28 x 10-3 M KOH c. 1.89 x 10-3 M HNO 3 d. 1.54 x 10-4 M Sr(OH) 2 Unit 11 Student Handout 6
25. Calculate the poh of each of the following solutions: a. 1.34 x 10-3 M HClO 4 b. 0.0211M NaOH c. 0.0109 M HBr d. 7.02 x 10-5 M Ba(OH) 2 Acid-Base Reactions 26. Write neutralization reactions for each of the following acids and bases. a. HI(aq) and NaOH(aq) b. HBr(aq) and KOH(aq) c. HNO 3 (aq) and Ba(OH) 2 (aq) d. HClO 4 (aq) and Sr(OH) 2 (aq) 27. Write neutralization reactions for each of the following acids and bases. a. HF(aq)and Ba(OH) 2 (aq) b. HClO 4 (aq) and NaOH(aq) c. HBr(aq) and Ca(OH) 2 (aq) d. HCl(aq) and KOH(aq) 28. Explain how a neutralization reaction is different from a dissociation equation. Provide an example of each. Acid-Base Titrations 29. Four solutions of unknown HCl concentration are titrated with solutions of NaOH. The following table lists the volume of each unknown HCl solution, the volume of NaOH solution required to reach the endpoint, and the concentration of each NaOH solution. Calculate the concentration (in M) of the unknown HCl solution in each case. HCl Volume (ml) [HCl] (M) NaOH Volume (ml) [NaOH] (M) (a) 25.00 ml 28.44 ml 0.1231 M (b) 15.00mL 21.22 ml 0.0972 M Unit 11 Student Handout 7
30. Four solutions of unknown NaOH concentration are titrated with solutions of HCl. The following table lists the volume of each unknown NaOH Solution, the volume of HCl solution required to reach the endpoint, and the concentration of each HCl solution. Calculate the concentration (in M) of the unknown NaOH solution in each case. NaOH Volume (ml) [NaOH] (M) HCl Volume (ml) [HCl] (M) (a) 5.00 ml 9.77 ml 0.1599M (b) 15.00 ml 11.34mL 0.1311M 31. A 25.00-mL sample of an H 2 SO 4 solution of unknown concentration is titrated with a 0.1328 M KOH solution. A volume of 38.33 ml of KOH was required to reach the endpoint. What is the concentration of the unknown H 2 SO 4 solution? Answ: 0.1018 M 32. A 5.00-mL sample of an H 3 PO 4 solution of unknown concentration is titrated with a 0.1221M NaOH solution. A volume of 5.99mL of the NaOH solution was required to reach the endpoint. What is the concentration of the unknown H 3 PO 4 solution? Answ: 0.0488 M 33. What volume in milliliters of a 0.101 M NaOH solution is required to reach the endpoint in the complete titration of a 10.0-mL sample of 0.138 M H 2 SO 4? Answ: 27.3 ml Unit 11 Student Handout 8
34. What volume in milliliters of 0.0992M NaOH solution is required to reach the endpoint in the complete titration of a 15.0-mL sample of 0.107 M H 3 PO 4? Answ: 48.6 ml Acid-Base Hydrolysis Hydrolysis occurs when certain salts dissolve in water to form solutions that have acidic or basic properties. A rule for predicting the properties of solutions of salts is based upon the concept of strong acids and strong bases in the Bronsted-Lowry sense. The rules are summarized in the table below: Salt formed from Water solution exhibits Example Strong acid + strong base no hydrolysis - neutral solutions KCl Strong acid + weak base hydrolysis to form acidic solution NH 4 SO 4 Weak acid + strong base hydrolysis to form basic solution Na 2 CO 3 Weak acid + weak base Must use K a and K b to determine Pb(C 2 H 3 O 2 ) 2 The commonly used strong acids are hydrochloric, nitric and sulfuric. The commonly used strong bases are sodium hydroxide, potassium hydroxide, and calcium hydroxide. Predict the hydrolysis effect of each of the following salts. For each answer write acidic, basic neutral or need K a and K b. 1. Na 3 PO 4 2. Na 2 SO 4 3. NaC 2 H 3 O 2 4. NH 4 NO 3 5. NH 4 Cl 6. Fe 3 (PO 4 ) 2 7. Ca(NO 3 ) 2 8. KC 2 H 3 O 2 9. CuSO 4 10. Al(NO 3 ) 3 11. NaCl 12. K 2 CO 3 Cummulative 35. A 0.125-g sample of a monoprotic acid of unknown molar mass is dissolved in water and titrated with 0.1003 M NaOH. The endpoint is reached after adding 20.77 ml of base. What is the molar mass of the unknown acid? Answ: 60.0 g/mol Unit 11 Student Handout 9
36. A 0.1O5-g sample of a diprotic acid of unknown molar mass is dissolved in water and titrated with 0.1288 M NaOH. The endpoint is reached after adding 15.2 ml of base. What is the molar mass of the unknown acid? Answ: 107 g/mol 37. Antacids, such as milk of magnesia, are often taken to reduce the discomfort of acid stomach or heartburn. The recommended dose of milk of magnesia is 1 teaspoon, which contains 400 mg of Mg(OH) 2. What volume of HCl solution with a ph of 1.1 can be neutralized by 1 dose of milk of magnesia? (Assume two significant figures in your calculations.) Answ: 170 ml 38. For each of the following strong base solutions, determine [OH - ], [H 3 O + ], and ph. a. 0.15M NaOH b. 8.7 x 10-5 M KOH 39. For each of the following weak base solutions, determine [OH - ], [H 3 O + ], and ph. a. Al(OH) 3 (Ksp = 3.0x10-34 ) b. Cd(OH) 2 (Ksp = 7.2x10-15 ) Unit 11 Student Handout 10
40. Methylamine, CH 3 NH 2, is a weak base. If the ph of a 0.065 M solution of the amine is 11.70, what is the value of K b? Answ: 3.8x10-4 M 41. A popular classroom demonstration consists of filing notches into a new penny and soaking the penny in hydrochloric acid overnight. Since new pennies are made of zinc coated with copper, and since hydrochloric acid dissolves zinc and not copper, the inside of the penny is dissolved by the acid, while the outer copper shell remains. Suppose the penny contains 2.5 g of zinc and is soaked in 20.0mL of 6.0M HCl. Calculate the concentration of the HCl solution after all of the zinc has dissolved. Calculate the ph and poh of the resulting solution. Answ: [HCl] = 2 M, ph = -0.3, poh = 14.3 42. What is the ph of a solution formed by mixing 125.0 ml of 0.0250 M HCl with 75.0 ml of 0.0500M NaOH? Answ: ph = 11.5 43. Calculate the hydroxide ion concentration and the ph of the solution that results when 22.0 ml of 0.15 M of acetic acid is mixed with 22.0 ml of 0.15 M NaOH. (Remember salt hydrolysis. What type of salt is formed from the reaction of acetic acid with NaOH? What side-reaction will occur as a result of this salt dissolving in water? Kb: C 2 H 3 O 2 - = 5.6x10-10 ) Answ: [OH - ]=6.5x10-6 M, poh = 5.2, ph = 8.8 (The side reaction is the acetate conj base reacting with water!) Unit 11 Student Handout 11
44. How many H + (or H 3 O + ) ions are present in one drop (0.050 ml) of pure water at 25 C? Answ: [H 3 O + ]=1.x10-7 M, 3.0x10 12 ions 60. You are titrating a 50.0 ml sample of hydrochloric acid with 0.250 M potassium hydroxide. After you have already added 42.3 ml of the potassium hydroxide you realize that you forgot to add the phenolphthalein indicator. When you add the indicator, the solution turns bright pink indicating that you have already missed the end point. You decide to back-titrate by adding 0.100 M nitric acid. The solution turns colorless after an addition of 10.1 ml of the nitric acid. What is the concentration of the original solution of hydrochloric acid? Answ: 0.192 M Unit 11 Student Handout 12