**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, C _{10}H_{20}N_{2}S_{4} (fw =
296.54). The sulfur in a 0.4329 g. sample of an Antabuse preparation was
oxidized to SO_{2}, which was absorbed in H_{2}O_{2
}to give H_{2}SO_{4}. The acid was titrated with 22.13
ml of 0.03736 M base. Calculate the percentage of the active ingredient.**

***2.Neohetramine, C _{16}H_{21}ON_{4
}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 (H _{2}C_{4}H_{4}O_{6};
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
(Na _{2}CO_{3}; fw = 106.0) should be taken to standardize
0.150M HClO_{4}, 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 BaCO_{3 }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 CO_{2} in the air (that is ml CO_{2}/106
ml air) if the density of CO_{2} is 1.98 g/l. Hint: First write
the equation for what is happening. Then determine the g of CO_{2},
then do the conversion to get the ppm CO_{2}.**

***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 NH _{3}**

**(b) 0.02 M in NH _{3 }and 0.04 M in
0.04 M NH_{4}Cl**

**(c) 0.03 M in NH _{4}Cl**

**(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 CO_{2} 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
(H_{2}O_{2}) to convert the sulfur dioxide to sulfuric
acid: SO_{2} + H_{2}O_{2} ®
H_{2}SO_{4} . 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 SO_{2} 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 + H_{2}O ®

b) NaCl + AgNO_{3} ®

c) ethlyamine + water ®

d) FeCl_{2} + KMnO_{4} + HCl ®
Mn^{+2} + Fe^{+3} + H_{2}O (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.

a) HClO

b) NaClO

c) ethylamine

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 AgNO_{3}

c) 0.01 M K_{2}CrO_{4}

4. Given a 0.5000 gram sample of pure CaCO_{3}. 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 Fe_{2}O_{3} in an iron ore.
It took 22.22 ml of a 0.06000 M K_{2}Cr_{2}O_{7}
solution to titrate a 0.6000 gram sample of the ore.

K_{2}Cr_{2}O_{7} + 6 Fe^{+2} + 14 H^{+}
® 2 K^{+} + 2 Cr^{+3} +
6 Fe^{+3} + 7 H_{2}O

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 AgNO_{3}
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
Fe_{2}O_{3}. Calculate the percent of Fe_{3}O_{4}
present in the ore if the mass of the precipitate is 0.6000 g.