# Acids and Bases Give the equation used to solve each problem and show all work. 5.76

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1 Acids and Bases Give the equation used to solve each problem and show all work. Name: Period: (1) Complete the following table. [H ] ph poh [OH ] 1.5x10 2 M acidic, basic, or neutral? x10 8 M neutral (2) Classify the following substances as acidic or basic and determine the [H ] and [OH ]. (a) Draino, ph = (c) Lye, poh = 2.60 (b) Vinegar, ph = 2.40 (d) Cola, poh = () Determine the ph and poh of the following solutions. (a) M HBr (c) 5.6x10 M LiOH (b) 1.2x10 4 M HNO (d) M Sr(OH) 2 Answers: (1) [H ] ph poh [OH ] acidic, basic, or neutral? 1.5x10 2 M x10 1 M acidic 5.8x10 9 M x10 6 M basic 6.0x10 12 M x10 M basic 2.6x10 7 M x10 8 M acidic 1.0 x10 7 M x10 7 M neutral (2) (a) basic [H ] =.2x10 1 M [OH] =.1x10 2 M (b) acidic [H ] = 4.0x10 M [OH] = 2.5x10 12 M (c) basic [H ] = 4.0x10 12 M [OH] = 2.5x10 M (d) acidic [H ] =.1x10 4 M [OH] =.2x10 11 M () (a) ph = 1.40 poh = (b) ph =.92 poh = (c) ph = poh = 2.25 (d) ph = poh = 1.40

2 BronstedLowry Acids and Bases Name: Period: (1) Write the formula for the conjugate base of the following acids. (a) HOCl (e) H BO (b) HNO 2 (f) H 2 PO 4 (c) H 2 SO (g) HSO 4 (d) H 2 CO (h) HC 2 O 4 (2) Write the formula for the conjugate acid of the following bases. (a) NH (e) H 2 PO 4 (b) C 6 H 5 NH 2 2 (f) SO (c) CN 2 (g) CO (d) OBr (h) BO () Write a K a or K b expression for the following acid or base equilibria. Identify the conjugate acidbase pairs. (a) HCN (aq) H 2 O (l) H O (aq) CN (aq) (b) C 2 H 5 NH 2 (aq) H 2 O (l) (c) OCl (aq) H 2 O (l) (d) HSO (aq) H 2 O (l) OH (aq) C 2 H 5 NH (aq) OH (aq) HOCl (aq) H O (aq) SO 2 (aq) (4) Complete the following acid or base equilibria. Identify the conjugate acidbase pairs and write a K a or K b expression. (a) HIO (aq) H 2 O (l) (b) C 5 H 5 N (aq) H 2 O (l) (d) HONH 2 (aq) H 2 O (l) (e) [Cr(H 2 O) 6 ] (aq) H 2 O (l) (c) H 2 C 2 O 4 (aq) H 2 O (l) (5) Calculate the ph and poh for the following solutions. (a) 0.10 M HC 2 H O 2 (c) 0.06 HCN (b) 0.40 M NH (d) 0.42 M HONH 2 (6) The ph of M solution of Ascorbic Acid (HC 6 H 7 O 6 ) is 2.5. Determine K a. (7) The poh of a 0.40 M solution of Ephedrine (C 10 H 15 ON) is Determine K b. (8) Determine the percent dissociation for the following compounds. (a) 0.14 M HOCl (b) 0.25 M C 2 H 5 NH 2 (9) The percent dissociation for a M solution of Morphine (C 17 H 19 N) is 0.7%. Determine K b. (10) The percent dissociation for a M solution of formic acid (HCO 2 H) is.0%. Determine K a.

3 Answers: (1) (a) OCl (b) NO 2 (c) HSO (d) HCO (e) H 2 BO 2 (f) HPO 4 2 (g) SO 4 2 (h) C 2 O 4 (2) (a) NH 4 (b) C 6 H 5 NH (c) HCN (d) HOBr (e) H PO 4 (f) HSO (g) HCO 2 (h) HBO () (a) HCN (aq) H 2 O (l) H O (aq) CN (aq) (c) OCl (aq) H 2 O (l) OH (aq) HOCl (aq) a b ca cb b a cb ca [ HO ][ CN ] [ OH ][ HOCl] Ka Kb [ HCN] [ OCl ] (b) C 2 H 5 NH 2 (aq) H 2 O (l) OH (aq) C 2 H 5 NH (aq) b a cb ca [ OH ][ C2H5NH ] Kb [ C H NH ] (d) HSO (aq) H 2 O (l) H O (aq) SO 2 (aq) a b ca cb 2 [ HO ][ SO ] Ka [ HSO ] (4) (a) HIO (aq) H 2 O (l) H O (aq) IO (aq) a b ca cb [ HO ][ IO ] Ka [ HIO ] (b) C 5 H 5 N (aq) H 2 O (l) OH (aq) C 5 H 5 NH (aq) b a cb ca [ OH ][C5H5NH ] Kb [C H N] 5 5 (c) H 2 C 2 O 4 (aq) H 2 O (l) H O (aq) HC 2 O 4 (aq) a b ca cb [ HO ][ HC2O4 ] Ka [ H C O ] (d) HONH 2 (aq) H 2 O (l) OH (aq) HONH (aq) b a cb ca [ OH ][HONH ] Kb [HONH ] 2 (e) [Cr(H 2 O) 6 ] (aq) H 2 O (l) H O (aq) [Cr(H 2 O) 5 (OH)] 2 (aq) a b ca cb 2 [ HO ][[ Cr( H2O) 5( OH )] ] Ka [[ Cr( H O) ] ] 2 6 (5) (a) ph = 2.89 poh = (b) ph = 11.4 poh = 2.57 (c) ph = 5. poh = 8.67 (d) ph = 9.8 poh = 4.17 (6) K a = 8.2x10 5 (7) K b = 1.4x10 4 (8) (a) 0.050% (b) 4.8% (9) K b = 8.1x10 7 (10) K a =1.9x10 4

4 Acid Base Equilibria Name: Period: (1) Calculate and compare the ph of a 0.40 M solution of HNO and a 0.40 M solution of HNO 2. (2) Calculate the concentration if a solution of HCl has a ph of.00 and a solution of HF has a ph of.00 Compare the results. () At 50 ºC, water was Kw = 5.5x What is the ph of a neutral solution at this temperature? (4) Determine the K b value for the following bases. (a) F (b) OCl (c) HSO (5) Determine the K a value for the following acids. (a) HONH (b) C 2 H 5 NH (c) CH NH (6) (a) Rank the following substances from the strongest to weakest acid: HIO, HF, HClO 2, HCN. Explain. (b) Rank the following substances from the strongest to weakest base: IO, F, ClO 2, CN. Explain (7) (a) Rank the following substances from strongest to weakest base: N 2 H 4, C 2 H 5 NH 2, C 5 H 5 N, HONH 2. Explain (b) Rank the following substances from the strongest to weakest acid: N 2 H 5, C 2 H 5 NH, C 5 H 5 NH, HONH. Exlain. (8) A solution contains HSO. Write two equations to show that this compound is amphoteric and determine an equilibrium constant for each. Would the solution be acidic or basic? (9) Complete the following acidbase equilibria. Calculate an equilibrium constant for the reaction. Does the equilibrium favour the reactants or products? Which is the stronger acid in the equilibrium? Which is the stronger base in the equilibrium? (a) CH NH 2 (aq) HOBr (aq) (b) HONH 2 (aq) HOCl (aq) (10) Calculate the ph and poh of a solution containing 0.10 M HBr and 0.10 M HOBr (11) Calculate the ph and poh of a solution containing M LiOH and M N 2 H 4. (12) Calculate the ph and poh of a mixture containing 0.20 M HNO 2 and 0.20 M HOCl. (1) Calculate the ph and poh of a mixture containing 0.25 M CH NH 2 and 0.25 M C 6 H 5 NH 2. (14) Calculate the ph and poh of a solution containing 0.50 M HNO 2 and 0.50 M NaNO 2 (15) Calculate the ph and poh of a solution containing 1.0 M CH NH 2 and 1.0 M CH NH Cl (16) Determine an equilibrium constant for the following reaction: H 2 S (aq) 2H 2 O (l) 2H O (aq) S 2 (aq) H 2 S (aq) H 2 O (l) H O (aq) HS (aq) K a1 = HS (aq) H 2 O (l) H O (aq) S 2 (aq) K a2 =

5 Answers: (1) HNO ph = 0.40 HNO 2 ph = 1.90 A solution of a strong acid will have a much lower ph that a solution of a weak acid with the same initial concentration. (2) [HCl] = 1.0x10 M [HF] = M A solution of a strong acid will have a much lower concentration that a solution of a weak acid with the same ph. () ph = 6.6 (4) (a) K b = 1.4x10 11 (b) K b = 2.9x10 7 (c) K b = 6.7x10 1 (5) (a) K a = 9.1x10 7 (b) K a = 1.8x10 11 (c) K a = 2.x10 11 (6) (a) HIO > HClO 2 > HF > HCN The larger the K a, the stronger the acid. (b) CN > F > ClO 2 > IO The stronger the acid, the weaker the conjugate base; the weaker the acid, the stronger the conjugate base. (7) (a) C 2 H 5 NH 2 > N 2 H 4 > HONH 2 > C 5 H 5 N The larger the K b, the stronger the base. (b) C 5 H 5 NH > HONH > N 2 H 5 > C 2 H 5 NH The stronger the base, the weaker the conjugate acid; the weaker the base, the stronger the conjugate acid. (8) acid: HSO (aq) H 2 O (l) H O (aq) SO 2 (aq) K a = 1.0x10 7 base: HSO (aq) H 2 O (l) OH (aq) H 2 SO (aq) K b = 6.7x10 1 The solution would be acidic since K a > K b. (9) (a) K = 88 Since K>1, the equilibrium favours the products. HOBr is a stronger acid than CH NH, and CH NH 2 is a stronger base than OBr. (b) K = 0.09 Since K<1, the equilibrium favours the reactants. HONH is a stronger acid than HOCl, and OCl is a stronger base than HONH 2. (10) ph = 1.00 and poh = 1.00 (11) ph = 12,70 and poh = 1.0 (12) ph = 2.05 and poh = (1) ph = and poh =2.00 (14) ph =.40 poh = (15) ph = poh =.6 (16) K = K a1 x K a2 = 1.x10 20

6 Salts and Buffers Name: Period: (1) Determine if the following salts will be acidic, basic, or neutral. Explain. (a) lithium chloride, LiCl (d) pyridinium chlorite, C 5 H 5 NHClO 2 (b) potassium cyanide, KCN (e) ethylammonium nitrite, C 2 H 5 NH NO 2 (c) ammonium chlorate, NH 4 ClO (f) barium bromide, BaBr 2 (2) Calculate the ph and poh of the following salts. (a) M methylammonium iodide, CH NH I (b) M sodium fluoride NaF (d) M potassium acetate, KC 2 H O 2 (e) 0.50 M ammonium hypochlorite, NH 4 OCl (c) 0.20 M hydroxylammonium nitrate, HONH NO () Calculate the ph of the following buffer solutions. How does the ph compare to the pk a? Explain. (a) 0.50 M HNO 2 and 0.50 M NaNO 2 (c) 0.50 M HNO 2 and 0.40 M NaNO 2 (b) 0.40 M HNO 2 and 0.40 M NaNO 2 (d) 0.40 M HNO 2 and 0.50 M NaNO 2 (4) What reaction will occur when a strong base is added to the buffer in question #. What will be the effect on ph if a strong base is added to this buffer? (5) What reaction will occur when a strong acid is added to the buffer in question #. What will be the effect on ph if a strong acid is added to this buffer? (6) Define buffer capacity. A 1.0 L sample of which solution in question # would have the highest buffer capacity? Explain. (7) Calculate the poh and ph the following buffer solution: 0.25 M NH and 0.25 M NH 4 I (8) (a) Determine the ph and poh of a buffer prepared by adding 0.50 g of sodium fluoride (NaF) to 400 ml of M hydrofluoric acid (HF). Assume the volume of the solution remains constant. (b) Determine the ph and poh of a buffer prepared by adding 4.85 g of hydrazinium chloride (N 2 H 5 Cl) to 600 ml of 0.24 M hydrazine (N 2 H 4 ). Assume the volume of the solution remains constant. (9) Determine the mass of sodium acetate (NaC 2 H O 2 ) that must be added to 750 ml of 0.20 M acetic acid (HC 2 H O 2 ) in order to make a buffer with ph = Assume the volume of the solution remains constant (10) Determine the mass of triethylammonium chloride (C 6 H 15 NHCl) that must be added to 1.0 L of 0.40 M triethylamine (C 6 H 15 N) in order to make a buffer with ph = Assume the volume of the solution remains constant Answers: (1) (a) neutral (b) basic (c) acidic (d) acidic (K a >K b ) (e) basic (K b >K a ) (f) neutral (2) (a) ph = 6.2 poh = 7.77 (b) ph = 7.96 poh = 6.04 (c) ph =.87 poh = 10.1 (d) ph = 8.57 poh= 5.4 (e) ph = poh =.44 () (a) ph =.40 (ph = pk a because [HNO 2 ] = [NO 2 ]) (b) ph =.40 (ph = pk a because [HNO 2 ] = [NO 2 ]) (c) ph =.0 (ph < pk a because [HNO 2 ] > [NO 2 ]) (d) ph =.50 (ph > pk a because [HNO 2 ] < [NO 2 ]) (4) HNO 2 OH H 2 O NO 2, ph will increase because [HNO 2 ] decreases and [NO 2 ] increases. (5) NO 2 H O H 2 O HNO 2, ph will decrease because [HNO 2 ] increases and [NO 2 ] decreases. (6) Buffer Capacity: the amount of an acid or base that can be added to a volume of a buffer solution before its ph changes significantly (generally one ph unit). The buffer capacity is greatest when a buffer has ph closest to pk a (when the ratio of the concentration of conjugate base to acid is closest to one) and when the concentrations of the acid and the conjugate base are highest. A 1.0 L sample of solution "a" would have the highest buffer capacity since ph = pk a ([NO 2 ]/ [HNO 2 ] = 1)and it has the highest concentration of both [HNO 2 ] and [NO 2 ]. (7) poh = 4.74 ph = 9.26 (8) (a) ph =.6 poh =10.64 (b) poh = 5.21 ph = 8.79 (9) 9.2 g NaC 2 H O 2 (10) 70 g C 6 H 15 NHCl

7 ph Titrations Name: Period: (1) Give the net ionic equations the following neutralization reactions. (a) LiOH HI (b) HNO 2 KOH (c) NH HBr (d) hydrofluoric acid and sodium hydroxide (e) aniline (C 6 H 5 NH 2 ) and hydrochloric acid (2) What volume (in ml) of M NaOH is required to titrate ml of M HC 2 H O 2? () What is the concentration of ammonia if 0.00 ml of NH requires ml of 0.80 M HCl to titrate? (4) A sample of g on an unknown monoprotic acid (HA) is dissolved in water and titrated with 1.15 ml of M NaOH. Determine the molar mass of the unknown acid. (5) Strong Base/Strong Acid A M solution of HCl is used to titrate ml of a M NaOH solution. Determine the ph at the following intervals in the experiment. Graph the results. Label the equivalence point. (a) No HCl has been added ph = (e) ml of HCl has been added ph = (b) ml of HCl has been added ph = (f) 51.0 ml of HCl has been added ph = (c) ml of HCl has been added ph = (g) ml of HCl has been added ph = (d) ml of HCl has been added ph = (h) ml of HCl has been added ph = ph vs. Volume of HCl added Volume of HCl added (ml)

10 (10) Match each of the given titration curves to one of the following acids: HCl, H 2 CO, H PO 4, and HC 2 H O 2. Explain your reasoning. (a) (c) (b) (d) Answers: (1) (a) OH H H 2 O (b) HNO 2 OH NO 2 H 2 O (c) NH H O NH 4 H 2 O (d) HF OH F H 2 O (e) C 6 H 5 NH 2 H O C 6 H 5 NH H 2 O (2) 25.0 ml NaOH () 0.40 M NH (4) 152 g/mol (5) (a) (b) (d) 10.7 (e) 7 (f). (i) (6) (a) 2.87 (b) 4.27 (c) 4.74 (e) 8.72 (g) 12.0 (i) (j) At equivalence point: V = ml At half equivalence point: V = ml, ph = 4.74 Halfway to the equivalence point, ph = pk a = log (1.8x10 5 ) = 4.74 (k) The buffer region is before 100 ml of base have been added. In this region both the acid (HC 2 H O 2 ) and its conjugate base (C 2 H O 2 ) are present, making the solution a buffer. (l) At the end of the experiment, there is strong base present so the solution contains hydroxide ions making the ph high. (7) (a) (c) (d) (e) 5.91 (g) (i) 1.98 (j) At equivalence point: V = ml At half equivalence point: V = ml, poh =.6 Halfway to the equivalence point, poh = pk b = log (4.4x10 4 ) =.6 (k) The buffer region is before 40 ml of acid have been added. In this region both the base (CH NH 2 ) and its conjugate acid (CH NH ) are present, making the solution a buffer. (l) At the end of the experiment, there is strong acid present so the solution contains hydronium ions making the ph low. (8) Question 5: Use Bromothymol Blue since the ph at the equivalence point (7) is equal to the pk a for bromothymol blue Question 6: Use Phenolphthalein since the ph at the equivalence point (8.72) is closest to the pk a for phenolphthalein (9) Question 7: Use Methyl Red since the ph at the equivalence point (5.91) is closest to the pk a for methyl red (5) (9) The equivalent point is where the moles of acid are equal to the moles of base. The endpoint of a titration is where the indicator is observed to change colour. (10) (a) H 2 CO (diprotic, has two equivalence point) (b) HC 2 H O 2 (weak acid, begins at a moderately low ph and has a smaller change of ph around the equivalence point) (c) HCl (strong acid. begins at a very low ph and has a larger change of ph around the equivalence point) (d) H PO 4 (triprotic, has three equivalence points)

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