3. Determine the ph of a solution that is 0.75 M in hypochlorous acid and 0.35 M in sodium hypochlorite.

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Hortense Osborne
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1 HOMEWORK 2A 1. From the data given in Handout 3 on the class website, determine the pk a of the following acids. (a) Hydrocyanic acid (b) Hypochlorous acid (c) Formic acid 2. Determine if solutions of each of the following pairs of solutes constitutes a buffer (a) Hydrocyanic acid and sodium cyanide (b) Nitric acid and potassium nitrate. (c) Ammonia and ammonium chloride. 3. Determine the ph of a solution that is 0.75 M in hypochlorous acid and 0.35 M in sodium hypochlorite. 4. Determine the ph of a solution prepared by mixing 70.0 ml of a 0.10 M formic acid solution and 30.0 ml of a 0.10 M sodium formate solution. 5. From the data given in Handout 3 on the class website, determine the best weak acid conjugate base pair to prepare the following buffers. (a) A buffer of ph = 3.50 (b) A buffer of ph = 5.00 (c) A buffer of ph = Calculate the molar ratio of acid to conjugate base in a solution that has a ph of 9.00 and contains the weak acid hydrocyanic acid and a salt of its conjugate base, sodium cyanide.

2 HOMEWORK 2B 1. A solution is prepared by mixing 60.0 ml of a 0.10 M acetic acid solution and 40.0 ml of a 0.10 M sodium acetate solution. Will this be a buffer solution? Calculate the ph. Is this solution acidic or basic? 2. A solution is prepared by mixing 60.0 ml of a 0.10 M acetic acid solution and 40.0 ml of a 0.10 M sodium hydroxide solution. Will this be a buffer solution? Calculate the ph. Is this solution acidic or basic? 3. A solution is prepared by mixing 75.0 ml of a 0.40 M ammonia solution and 25.0 ml of a 0.60 M ammonium chloride solution. Will this be a buffer solution? Calculate the ph. Is this solution acidic or basic? 4. A solution is prepared by mixing 75.0 ml of a 0.40 M ammonia solution and 25.0 ml of a 0.60 M hydrochloric acid solution. Will this be a buffer solution? Calculate the ph. Is this solution acidic or basic? 5. A solution is prepared by mixing 10.0 ml of a 0.25 M hydrochloric acid solution and 40.0 ml of a 0.20 M potassium chloride solution. Will this be a buffer solution? Calculate the ph. What will be the concentration of the chloride ions in the solution? 6. A solution is 0.10 M in formic acid and M in sodium formate. (a) Calculate the ph of the solution. Is this solution acidic or basic? (b) Calculate the final ph if 0.10 gram of sodium hydroxide is added to 1.00 liter of the buffer solution, assuming the volume does not change. (c) Calculate the final ph if 1.0 gram of sodium hydroxide is added to 1.00 liter of the buffer solution instead of 0.10 gram, still assuming the volume does not change. 7. A buffer is prepared by mixing 20.0 ml of a 0.60 M ammonia solution with 10.0 ml of a 1.8 M ammonium chloride solution. (a) Calculate the ph of the solution. Is the solution acidic or basic? (b) Calculate the final ph if 1.0 ml of a 1.0 M hydrochloric acid solution is added to the buffer solution. (c) Calculate the final ph if 1.0 ml of a 1.0 M sodium hydroxide solution is added to the buffer solution instread of the hydrochloric acid solution.

3 HOMEWORK 2C 1. A 20.0 ml sample of a M hypochlorous acid solution is to be titrated with a M sodium hydroxide solution. (a) Calculate the ph of the hypochlorous acid solution at the beginning of the titration. (b) Calculate the ph of the resulting solution after 6.00 ml of the sodium hydroxide solution has been added to the 20.0 ml of the hypochlorous acid solution. (c) Calculate the ph of the resulting solution after ml of the sodium hydroxide solution has been added to the 20.0 ml of the hypochlorous acid solution. (d) Calculate the ph of the resulting solution after ml of the sodium hydroxide solution has been added to the 20.0 ml of the hypochlorous acid solution. (e) Calculate the moles and volume of the sodium hydroxide solution required to neutralize the hypochlorous acid. (f) Calculate the ph of the resulting solution at the equivalence point. (g) Calculate the ph of the resulting solution after ml of the sodium hydroxide solution has been added to the 20.0 ml of the hypochlorous acid solution. (h) Sketch the titration curve for the titration of M hypochlorous acid with M sodium hydroxide. Plot accurately the ph at the beginning of the titration, and after the addition of 6.00 ml, ml, ml, ml, and ml of the M sodium hydroxide. (i) From the list of indicators in Figure 15.8, what would be the best indicator for this titration? 2. The titration curve for a weak acid being titrated with a strong base is shown. Indicate the following. (a) The point on the titration curve when the solution contains only the weak acid (b) The point on the titration curve when the solution contains only the weak conjugate base (c) The point on the titration curve when the solution contains equal amounts of the weak acid and its weak conjugate base (d) The K a of the weak acid (e) From Table 15.8 in the textbook, determine the best indicator to use for this titration

4 HOMEWORK 2D 1. The solubility of silver phosphate in water is grams per liter at 20ºC. Calculate the solubility product, K sp, for this salt at 20ºC. 2. Using the solubility product constants for strontium carbonate and silver carbonate, determine which salt is more soluble in water. 3. At 30ºC, the solubility product, K sp, for magnesium fluoride is 8 x (a) Calculate the solubility of magnesium fluoride, in moles per liter and grams per liter, in pure water at 30ºC. (b) Calculate the solubility of magnesium fluoride, in moles per liter and grams per liter, in a solution that is M NaF at 30ºC. 4. Determine if the solubility of nickel (II) hydroxide will (1) increase, (2) decrease, or (3) remain the same with the addition of each of the following reagents. (a) Ni(NO 3 ) 2 (aq) (b) NaOH (aq) (c) HCl (aq) (d) NaCl (aq) 5. A solution is made 0.10 M in Mg 2+, and 0.10 M in NaOH. Will Mg(OH) 2 precipitate? HOMEWORK 2E 1. Calculate the concentration of silver ions needed to precipitate silver hydroxide in a buffer solution of ph A solution is made 0.10 M in Mg 2+, and Na 2 CO 3 is added until the CO 3 2- concentration is M. Calculate the percentage of Mg 2+ ions left in the solution at this point. 3. Iodide ions are slowly added to a solution containing M lead (II) ions and M silver ions. (a) What cation will be the first to precipitate? (b) What will be the concentration of the iodide ions when the first cation starts to precipitate? (c) What will be the concentration of the first cation when the second cation starts to precipitate? 4. In the precipitation of metal sulfides, selective precipitation can be achieved by adjusting the hydronium ion concentration. Calculate the ph that ZnS begins to precipitate from a water solution saturated with H 2 S (0.077 M) and containing 0.08 M Zn Calculate the solubility of FeS at ph 9.00 and at ph 2.00 in a water solution saturated with H 2 S (0.077 M). Can you see how its behavior might be useful in analytical separations?

5 HOMEWORK 2F 1. Find the Chart of the Nuclides on the internet at the web site for the National Nuclear Data Center, and complete the following data for data concerning all known isotopes of magnesium. Isotope Stable or Radioactive Natural Abundance Half-Life Decay Mode 2. Complete the following nuclear equations and supply symbols of values for X or x. (a) X 86Rn 4 2X XX (b) 14 XC X XN + 0-1β - (c) X XNe 19 XF β + (d) 75 XAs + 0-1e - X 32X (e) 235 XU + 1 0n x 1 0n X XX (f) 59 XCo + 2 1X 60 XCo + X XX 3. Write equations for each of the following nuclear processes. (a) beta positive decay by Sb (b) beta minus decay by 35 16S (c) alpha decay by Ra (d) electron capture by 7 4Be 4. What type of decay would you expect from each of the following radioisotopes? (a) 12 B (b) 55 Ni (c) 243 Am

6 HOMEWORK 2G 1. Radioactive Na with a half-life of 14.8 hours is injected into an animal in a tracer experiment. How many days will it take for the radioactivity to fall to 10.0% of its original intensity? 2. If g of 99 Mo decays by β - emission to g in 200. hours, what is the half-life of 99 Mo? 3. A sample of a radioisotope shows an activity of 100. disintegrations per minute. After 1.0 hour, the activity decreases to 77 disintegrations per minute. Determine the half-life of the radioisotope. 4. A sample of wood from an Egyptian mummy case gives 9.6 cpm g -1 of carbon of 14 C disintegrations. How old is the mummy case? 5. In a sample of uranite ore from the Black Hills of South Dakota, the mass of 206 Pb is 22.8% the mass of the 238 U present. Estimate a minimum age for the earth from this information. 6. Calculate the binding energy per nucleon for the following nuclear species. (a) 37 17Cl (m = u) (b) Pb (m = u) HOMEWORK 2R 1. Identify which of the following will result in a buffer solution when equal volumes of the two solutions are mixed. (a) 0.10 M KNO 3 and 0.10 M HNO 3 (b) 0.10 M NaNO 2 and 0.10 M HNO 2 (c) 0.20 M NaOH and 0.10 M HNO 2 (d) 0.10 M NaOH and 0.20 M HNO 2 (e) 0.10 M HCl and 0.10 M NH 3 (f) 0.20 M HCl and 0.10 M NH 3 (g) 0.10 M HCl and 0.20 M NH 3 2. Hypobromous acid has a K a of 2.5 x (a) Calculate the ph of a 0.25 M hypobromous acid solution. (b) Calculate the percent ionization of hypobrous acid. (c) Calculate the ph of a solution that is 0.25 M in hypobromous acid and 0.45 M in sodium hypobromite. 3. At 15 C, hypochlorous acid has a K a of 2.9 x (a) Calculate the ph of a 0.45 M hypochlorous acid solution. (b) Calculate the ph of a solution in which ml of the 0.50 M hypochlorous acid solution is mixed with ml of a 0.30 M in sodium hypochlorite solution. (c) Calculate the ph if moles of NaOH is added to the buffer solution in (b). (d) Calculate the ph if moles of HCl is added instead to the buffer solution in (b). (continued on next page)

7 4. A buffer is prepared by mixing 60. ml of a 0.50 M ammonia solution with 40. ml of a 0.90 M ammonium chloride solution. The solution is divided into to equal 50. ml portions (a) Calculate the ph of the buffer solution. (b) If 5 ml of a 1.0 M hydrochloric acid solution is added to the first 50. ml portion of the buffer, what will be its final ph? (c) If 5 ml of a 1.0 M sodium hydroxide solution is added to the second 50. ml portion of the buffer, what will be its final ph? 5. Determine the volume of 0.50 M hydrofluoric acid that must be mixed with 50.0 ml of 0.30 M sodium hydroxide to produce a buffer with ph = Given the following K a values: H 2 CO 3 + H 2 O H 3 O HCO 3 HCO H 2 O H 3 O CO 3 K a1 = 4.3 x 10-7 K a2 = 5.6 x A ph = buffer is to be prepared by mixing mL of 0.50 M sodium bicarbonate with the correct volume of 2.0 M sodium hydroxide. Calculate the volume of the sodium hydroxide solution needed to prepare the buffer. 7. A 20.0 ml sample of 0.10 M hydrocyanic acid solution is to be titrated with a 0.20 M sodium hydroxide solution. (a) Calculate the volume of 0.20 M sodium hydroxide to reach the endpoint of the titration. (b) Calculate the ph of the hydrocyanic acid solution before the titration. (c) Calculate the ph of the solution after 1.0 ml of the sodium hydroxide solution was added. (d) Calculate the ph of the solution after 5.0 ml of the sodium hydroxide solution was added. (e) Calculate the ph of the solution after 10.0 ml of the sodium hydroxide solution was added. (f) Calculate the ph of the solution after 15.0 ml of the sodium hydroxide solution was added. (g) Calculate the ph of the solution after 19.0 ml of the sodium hydroxide solution was added. (h) Calculate the ph of the solution after 20.0 ml of the sodium hydroxide solution was added. (i) From the list of indicators in Figure 15.8, what would be the best indicator for this titration? 8. Answer the following questions concerning the titration of acid HY with sodium hydroxide, using the curve to the right. (a) Which indicator would be best for the titration: thymol blue, bromcresol purple, or thymolphthalein? (b) What is the K a of the acid HY? (c) Where on the titration curve would you find all HY in the solution? (d) Where on the titration curve would you find half HA and half Y - in the solution? (e) Where on the titration curve would you find all Y - in the solution? (continued on next page)

8 9. Answer the following questions concerning the titration of acid H 2 X with hydroxide, using the curve to the right. (a) What is the K a1 of the acid H 2 X? (b) What is the K a2 of the acid H 2 X? (c) Where on the titration curve would you find all H 2 X in the solution? (d) Where on the titration curve would you find half H 2 X and half HX - in the solution? (e) Where on the titration curve would you find all HX - in the solution? (f) Where on the titration curve would you find half HX - and half X 2- in the solution? (g) Where on the titration curve would you find all X 2- in the solution? 10. Sketch a titration curve for each of the following titrations. For each, identify the ph before the titration, at the half-neutalization point, and at the equivalence point. (a) 0.10 M nitric acid being titrated with 0.10 M potassium hydroxide (b) 0.10 M hydrofluoric acid being titrated with 0.10 M potassium hydroxide.. (c) 0.10 M ammonia being titrated with 0.10 M hydrochloric acid. 11. The solubility of chromium (III) fluoride in water is grams per liter at 20ºC. Calculate the solubility product, K sp, for this salt at 20ºC. 12. Using the solubility product constants, determine the more soluble salt in each pair (a) lead (II) bromide and silver hydroxide (b) iron (II) carbonate and silver phosphate 13. At 20ºC, the solubility product, K sp, for lead (II) bromide is 4.6 x (a) Calculate the solubility of lead (II) bromide in moles per liter and grams per liter in pure water at 20ºC. (b) Calculate the solubility of lead (II) bromide in moles per liter and grams per liter in a solution that is 0.10 M Pb(NO 3 ) 2 at 20ºC. 14. The solubility product, K sp, for silver sulfate is 1.2 x If 20.0 ml of a 0.10 M silver nitrate solution is added to 30.0 ml of a 0.20 M sodium sulfate solution, does a precipitate of silver sulfate form? 15. Calculate the concentration of silver ions needed to precipitate silver sulfate in a solution that is 0.25 M in sodium sulfate. 16. A solution is made 0.10 M in Pb 2+, and NaCl is added until the Cl - concentration is M. Calculate the percentage of Pb + ions left in the solution at this point. (continued on next page)

9 17. Chromate ions are slowly added to a solution containing M barium ions and M silver ions. (a) What cation will be the first to precipitate? (b) What will be the concentration of the chromate ions when the first cation starts to precipitate? (c) What will be the concentration of the first cation when the second cation starts to precipitate? 18. Calculate the ph that MnS begins to precipitate from a water solution that is saturated with H 2 S (0.077 M) and containing 0.10 M Mn Calculate the solubility of MnS (a) at ph and (b) at ph 1.00 in a water solution that is saturated with H 2 S (0.077 M). 20. The following reaction produces the orange dichromate ion: Ag 2 Cr 2 O 7 (s) 2Ag + (aq) + Cr 2 O 7 2- (aq) The absorbances of five standard dichromate ion solutions were measured with a spectrometer in a 1.00 cm cuvet at 495 nm, and a plot of the absorbance of each solution against their concentrations is given below, including the equation for the calibration line. To determine the solubility product constant for silver dichromate, an equilibrium solution was prepared by mixing ml of M AgNO 3 with ml of M K 2 Cr 2 O 7. The absorbance of this solution was measured in a 1.0 cm cuvet with a spectrometer set at a wavelength of 495 nm, and found to be (a) Calculate the initial concentrations of Ag + and Cr 2 O 7 2- in the equilibrium solution. (b) Determine the equilibrium concentration of Cr 2 O 7 2- in the equilibrium solution. (c) Calculate the value for the K sp of Ag 2 Cr 2 O Predict the type of nuclear decay for each of the following radioisoptopes. (a) 13 7N (b) 69 30Zn (c) Po 22. Write equations for each of the following nuclear processes. (a) beta positive decay by Tb (b) beta minus decay by I (c) alpha decay by Ac (d) electron capture by 50 26Fe (e) spontaneous fission of Pu (continued on next page)

10 23. Complete the following nuclear equations. (a) 238 XNp + 1 0n x 1 0n X XX (b) 40 XAr + 2 1X 38 XCl + X XX 24. Calculate the binding energy per nucleon for the following nuclear species. (a) 10 5B (m = u) (b) Hg (m = u) 25.Which one of the following nuclei would be expected to have a higher binding energy per nucleon? (a) 8 4Be (b) 65 Zn (c) 235 U 26. Radioactive fluorine-18, with a half-life of 110. minutes, is used for imaging in PET scans. How many hours will it take for the radioactivity of the fluorine-18 to fall to 10.0% of its original intensity? 27. A sample of vanadium-42 shows an activity of 100. disintigrations per second. After one minute, the activity decreases to 83 disintigrations per second. Determine the half-life of vanadium A sample of bone gives 12.4 cpm g -1 of carbon of 14 C disintegrations. How old is the bone? HOMEWORK 2R ANSWERS 1. b, d, g 2. (a) 4.60 (b) 0.01% (c) (a) 3.94 (b) 7.62 (c) 7.78 (d) (a) 9.18 (b) 8.89 (c) ml ml 7. (a) 10. ml (b) 5.10 (c) 8.25 (d) 9.21 (e) (f) (g) (h) (i) alizarin yellow 8. (a) bromcresol purple (b) 1 x 10-2 (c) (d) (e) below to the left (continued on next page)

11 9. (a) 1 x 10-2 (b) 3 x 10-7 (c) (d) (e) (f) (g) below to the right 10. (a) (b) (c) x , 1.48, , 3.14, , 9.26, (a) PbBr 2 (b) Ag 3 PO (a) M, 3.8 g/l (b) M, 1.2 g/l 14. Yes x 10-3 M % 17. BaCrO 4 (b) 8.x M (c) M (a) 3.0 x M (b) 3.0 x 10 8 M 20. (a) M Ag + 2-, M Cr 2 O 7 2- (b) M Cr 2 O 7 (c) 4.6 x 10-6 (continued on next page)

12 21. (a) beta positive decay or electron capture (b) beta minus decay (c) alpha decay or spontaneous fission 22. (a) Tb Gd β + (b) I Xe + 0-1β - (c) Ac Fr + 4 2α (d) 50 26Fe + 0-1e Mn (e) Pu Y ZX Y N 94 ZX + N 1 0n 23. (a) Np + 1 0n 5 1 0n Zr I (b) 40 18Ar + 2 1H 38 17Cl α 24. (a) MeV/nucleon (b) MeV/nucleon Zn hours minutes 28. 1,740 years

6. From the data given in Handout 1 on the class website, determine the best weak acid conjugate base pair to prepare a buffer of ph = 9.00.

6. From the data given in Handout 1 on the class website, determine the best weak acid conjugate base pair to prepare a buffer of ph = 9.00. EXTRA REVIEW 2A 1. A solution is prepared by mixing 80.0 ml of a 0.50 M nitrous acid solution and 20.0 ml of a 0.25 M sodium nitrite solution. Will this be a buffer solution? Calculate the ph. Is this