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FOR EACH OF THE FOLLOWING PROBLEMS THE STUDENT SHOULD READ THE PROBLEM, IDENTIFY THE TYPE, AND THEN DO THE SET-UP, SUBSTITUTION, AND FIND THE ANSWER. REMEMBER TO USE UNITS AND SIGNIFICANT FIGURES. THE GOOD STUDENT WILL WORK ALL PROBLEMS. IF YOU CAN ONLY DO PART TO THE ASSIGNMENT DO THE PROBLEMS WITH A *. PREFERRED DUE DATE IS FRIDAY, 4/20. PROBLEMS WILL BE ACCEPTED UNTIL 4/27. These are all good review for the test.
*1. The active ingredient in Antabuse, a drug used for the treatment of chronic alcoholism, is tetraethylthiuram disulfide, C10H20N2S4 (fw = 296.54). The sulfur in a 0.4329 g. sample of an Antabuse preparation was oxidized to SO2, which was absorbed in H2O2 to give H2SO4. The acid was titrated with 22.13 ml of 0.03736 M base. Calculate the percentage of the active ingredient.
*2.Neohetramine, C16H21ON4 fw = 285.37, is a common antihistamine. A 0.1247 g. sample containing this compound was analyzed by the Kjeldahl method. The ammonia produced was collected in 5.000 ml of 0.1000 M HCl. The excess HCl was titrated with 7.42 ml of 0.01477 NaOH. Calculate the percentage of neohetramine in the sample.
*3. A 0.2296 g sample of a recrystallized organic acid required a 29.83 ml titration with 0.1000 M NaOH to reach the phenolphthalein end point. What is the equivalent weight of the acid (that is, the number of grams of acid per mole of titratable protons)?
4. A 50.00 ml sample of a white dinner wine required 21.48 ml of 0.03776 M NaOH to achieve a phenolphthalein end point. Express the acidity of the wine in terms of grams of tartaric acid (H2C4H4O6; fw = 150.09) per 100 ml. (assume that the two hydrogens are titrated.)
*5. What weight of standard benzoic acid (fw = 122, one proton) must be taken to standardize some 0.050 M NaOH if the desired volume for the titration is 38 ml of titrant.
6. What weight of standard sodium carbonate (Na2CO3; fw = 106.0) should be taken to standardize 0.150M HClO4, If the desired volume is 41 ml of the acid.
*7. A 3.00 lites sample of urban air was bubbled through a solution containing 50.00 ml of 0.0116 M Ba(OH)2, and BaCO3 precipitated. The excess base was back titrated to a phenolphthalein endpoint with 23.6 ml. of 0.0108 M HCl. Calculate the parts per million of CO2 in the air (that is ml CO2/106 ml air) if the density of CO2 is 1.98 g/l. Hint: First write the equation for what is happening. Then determine the g of CO2, then do the conversion to get the ppm CO2.
*8. A student decides to standardize a solution of NaOH with phenolphthalein. The student dissolves 6.123 g. of 99.95% pure potassium acid phthalate (fw= 204.2) in a 250 ml. volumetric flask. A 30.00 ml aliquot required 42.35 ml of the base to reach the phenolphthalein end point. Calculate the Molarity of the base.
*9. A student has synthesized a new acid. A 0.6666 g sample is titrated with 0.09892 M NaOH. The titration with acid is done using a pH meter. The curve has a gentle rise and then a sharp rise at 45.00 ml. The mid point of the rise was at a pH of 10.02 At 22.50 ml the pH read 4.75. (a) calculate the equivalent weight of the acid. (b) Calculate the pKa of the acid. (c) suggest a suitable indicator for the titration with indicators (if you cannot give a name tell the criteria that you would use to choose the indicator). (d) What is the formula weight of the acid?
*10. Given 50.00 ml of 0.1500 M HA (Ka = 2 x 10-6). Calculate the pH for each of the following solutions: (a) The initial solution; (b) The solution which results when 20.00 ml of 0.1200 M NaOH has been added; (c) The solution which results when 50.00 ml of 0.01500 M NaOH is added; (d) the solution which results when 50.00 ml of 0.200 M NaOH has been added.
*11. Calculate the pH of a solution which is:
(a) 0.01 M in NH3
(b) 0.02 M in NH3 and 0.04 M in 0.04 M NH4Cl
(c) 0.03 M in NH4Cl
(d) 0.03 M in HOAc
(e) 0.05 M in HOAc and 0.05 M in NaOAc
(f) 0.06 M in NaOAc and 0.02 M in HOAc
(g) 0.02 M in NaOAc
(h) 0.02 M in NaCl
(i) 0.018 M in HBr
(j) 0.015 M in KOH
*12. What is the best indicator for a titration whose pH at the equivalence point is:
(a) 3.5; (b) 5.4: (c) 7.0 (d) 8.3 (e) 9.5 (f) 10.2
Think about using Methyl red, bromothymol blue and phenolphthalein. Will you need additional indicators.
*13. Bill gets a mean of 43.24% KHP on Monday with s = .20 and 4 samples. On Thursday he gets a mean of 43.01% with 5 samples and s = 0.20. Do his numbers indicate that he is using the same unknown?
*14. Given the following data: .4444; .4456; .4467; .4479; .4495; .4466; .4666.
Calculate the mean, median, standard deviation, and average standard deviation.
*15. Look at the data in problem 14. Can you reject any of the given data? If so do and rework the problem.
*16. Given the following 2 data sets: Set a: .4444; .4467; .4479; .4495;
Set b: .4446, .4466, 4466, .4658, .4482.
Do these two sets come from the same source at a 95% CL or at a 90% CL?
For either of these sets do you feel that a data point should be rejected?
CHM 210 PROBLEMS
FOR GOOD REVIEW, WORK EACH OF THE FOLLOWING PROBLEMS, SHOW SETUPS, SUBSTITUTIONS AND ANSWERS. ANSWERS WILL BE POSTED.
1.A solution of Ba(OH)2 was standardized against 0.1016 g. of primary standard benzoic acid (HBz, FW = 122.12 g). An end point was observed after addition of 44.42 mL of base. Calculate the molarity of the base.
Ba(OH)2 + 2 HBz ® 2 HOH + other ions
2. Exactly 40.00 ml of HCl was added to a solution containing 0.4793 g of primary standard (99.95% pure) sodium carbonate. The solution was boiled to remove CO2 and the excess HCl was back-titrated with 8.70 ml of a NaOH solution. In a separate experiment, 25 ml of the NaOH neutralized 27.43 ml of HCl. Calculate the molarity of the HCl and the NaOH.
3. The sulfur in a 0.5073 gram sample of coal was burned in a stream of oxygen gas. The combustion products were bubbled through hydrogen peroxide (H2O2) to convert the sulfur dioxide to sulfuric acid: SO2 + H2O2 ® H2SO4 . Titration of the sulfuric acid required 33.29 ml of 0.1115 M NaOH. Calculate the percent sulfur in the coal sample. Calculate the percent of SO2 in the coal sample.
4. Calculate the pH of the following solutions:
a. 0.01 M HBr
b. 0.01 M KOH
c. 0.01 M RbI
d. 0.01 M Ba(OH)2
5. A weak acid, HX, is 1.0% dissociated in a 0.050 M solution.
a) Calculate the value of Ka for the weak acid.
b) Calculate the percentage dissociated in a 0.10 M solution.
c) At what concentration is the acid 2% dissociated?
6. A weak base, B, has a molecular weight of 80.0 g/mole. A solution is prepared by dissolving 2.00 gram of B in 200 ml of water. The solution has a pH of 9.70. Calculate the dissociation constant of B.
THIS SET OF PROBLEMS SHOULD TAKE YOU ABOUT AN HOUR. IT HAS BEEN DESIGNED AS A REVIEW TO HELP YOU PREPARE FOR THE TEST ON 4/25. EACH PROBLEM SHOULD MAKE YOU THINK. YOU WILL ALSO HAVE TO CHANGE TOPICS WHEN GOING FROM ONE PROBLEM TO ANOTHER PROBLEM.
SHOW ALL SETUPS AND SUBSTITUTIONS FOR NUMERICAL PROBLEMS. FOR CALCULATION OF pH REMEMBER TO SHOW CONC OF HYDROGEN ION AND THEN pH (I KNOW YOU USE THE CALCULATOR).
1. Give the equilibrium constant expressions for the following reactions. You may need to consult tables or balance equations before you begin.
a) HClO + H2O ®
b) NaCl + AgNO3 ®
c) ethlyamine + water ®
d) FeCl2 + KMnO4 + HCl ® Mn+2 + Fe+3 + H2O (unbalanced)
2. Calculate the pH of a 0.01 M aqueous solution of each of the following solutions. Use the approximate formula. Leave the quadratic equation for other problems! Also identify all conjugate acid base pairs in this problem.
d) ethylamine hydrochloride
3. Calculate the solubility of silver chromate in grams per liter in each of the following solvents.
a) deionized water
b) 0.01 M AgNO3
c) 0.01 M K2CrO4
4. Given a 0.5000 gram sample of pure CaCO3. This solution was titrated with 43.22 ml of an HCl solution. Calculate the molarity of the HCl solution. What was the pH of the HCl solution. What was the ppm of Chloride ion in the HCl solution. HINT: Write the balance equation before you begin.
5. Calculate the percent of Fe2O3 in an iron ore. It took 22.22 ml of a 0.06000 M K2Cr2O7 solution to titrate a 0.6000 gram sample of the ore.
K2Cr2O7 + 6 Fe+2 + 14 H+ ® 2 K+ + 2 Cr+3 + 6 Fe+3 + 7 H2O
6. A 2.4000 gram sample of KCl which is 95.22% pure is dissolved in a 250 ml volumetric flask. A 25 ml aliquot required 42.21 ml of AgNO3 to reach the endpoint. Calculate the molarity of the silver nitrate solution.
7. A 0.5431 gram sample of iron ore is dissolved in acid and is precipitated as Fe(OH)3. The precipitate is filtered and ignited to form Fe2O3. Calculate the percent of Fe3O4 present in the ore if the mass of the precipitate is 0.6000 g.