Chem 112, Test 1 -- January 21, 2005 -- page 1
Name _________________________
You are allowed 2 consecutive hours (no cutting classes) for this test. You may use your calculator but NO extra
“scratch paper”. Be sure to sign the pledge at the end of the test. START TIME: ________ ; END TIME: _________
LECTURE: Multiple Choice -- (20 pts) 2 points each. Choose the best answer and write your
answer legibly to the left of the question. (No circling or filling in the choices; too confusing)
1) What is it that distinguishes a Major Reaction from a Minor Reaction?
a) the fact that Minor Reactions produce very little products compared to amounts of
reactants; at equilibrium most of the reactants still remain
b) the fact that Le Chatelier’s Principle only applies to Minor Reactions
c) the fact that Minor Reactions have associated with them a Keq value
d) the fact that Major Reactions are characterized by a Limiting Reagent calculation
e) all the above distinguish a Major Reaction from a Minor Reaction
2) For what case is the final description of an aqueous solution of a substance apt to
differ the most from the bulk formula for that substance?
a) when the bulk formula is of a molecular compound
b) when the bulk formula is of a completely soluble ionic substance
c) when the bulk formula consists completely of Non-metallic elements
d) when the bulk formula is for a pure metal
e) when the bulk formula is that of an Acid/Base Indicator
3) When you say you are trying to carry out a Standardization, what are you trying to
achieve:
a) you are trying to determine the concentration of the titrant
b) you are trying to determine the concentration of the analyte
c) You are trying to determine the concentration of the titrant to high quality
d) You are trying to determine the concentration of the analyte to high quality
e) You are trying to obtain a solution whose concentration is 0.1000 M
f) 3 of the above
g) 2 of the above
4) Given the generic reaction: 2A +
B ↔
C
+
2D, where
Keq = 1.00 x10-2, if a solution finds itself with [A] = 0.02, [B] = 0.1,
[C] = 0.006, and [D] = 0.01, what change will be observed?
a) no change will be observed; the solution is at equilibrium
b) reactants A and B will be converted into products C and D
c) products C and D will be converted into reactants A and B
d) because the specific amounts (amounts in grams and overall volume) of the four
substances are not provided, it is not possible to come to an evaluation
Chem 112, Test 1 -- January 21, 2005 -- page 2
5) In the first lab exercise, Lab Zero, you were told to determine the % Relative
Uncertainty of a processed measurement. The measurement which most influenced the
value you were able to write down for the % Relative Uncertainty for this processed
measurement was:
a) the volume of water used
b) the weight of water used
c) the calculated density value
d) the molecular weight of water
6) Which of the following statements apply to both a major rxn and a minor rxn?
a) can be characterized by a Keq expression
b) implies the presence of a limiting reagent
c) can be used as a titration reaction
d) rxn takes place at the particle level
e) all of the above
f) none of the above
7) When in aqueous solution, a substance whose bulk formula is NaX generates a
species with a Kb = 3 x 10-5, it is also true that
a) The X in the bulk formula will be X- in solution
b) the conjugate will have the formula HX
c) the conjugate is a weak acid with a Ka
d) the bulk substance will not completely dissolve in water, because it’s a weak base
e) all of the above are true
f) 3 of the above are true
8) If you are given the Ka value for the solution component H2PO4- , which of the
following will you NOT be able to determine?
a) the pKa for H2PO4b) the pKb for H2PO4c) the Kb for HPO42d) the pKb for HPO42e) you will be able to determine all of the above K’s
9) In the KHP determination, the species which is defined as the analyte is:
a) the species doing the titrating, here OHb) the actual bulk species making up the titrant, here NaOH
c) the species in the beaker actually being titrated, here HPd) the bulk species which was in your sample unknown, here KHP
e) the formula of the species which you will ultimately report; this could vary depending
on the requirements of the titration
10) Given the mathematical operation (2)(π)(13.5 g/mL) / (0.030 L) (33.56 sec) how
many significant figures will your answer contain?
a) 1 b) 2 c) 3 d) 4 e) it’ll depend on the value of π that you use
Chem 112, Test 1 -- January 21, 2005 -- page 3
FUNDAMENTALS (37 pts): Short answers. Be precise and concise
1. Define what is meant by the term measurement.
2. We speak in this course of the wish to be able to characterize a solution. What is meant by
Characterizing a Solution? ______________________________________________________________
3. What is the distinction between a Counter Ion and a Conjugate Ion in this course?
4. What is the most significant and important property of a Primary Standard?
5. Write down the bulk formula of a base which has no conjugate acid: __________________________
6. If four solutions have pH values of 5.24, 8.71, 0.70, and 10.35,
which is the most acidic? ______________ which is the most basic? __________________________
7. If pH = 5.12, what is: [H3O+]? ____________ ; [OH-] ? _____________ pOH? ______________
8. If three substances have pKa values of 9.21, 6.65, and 4.32,
which is the strongest acid? __________? Which will have the strongest conjugate base? ___________
9. Given the species: H2PO4- , H3PO4, CO32- , CH3NH3+, HClO4
a) which species (can be > 1) has a Ka value and also a Kb value? ______________________________
b) and what is the relationship between the two K’s in question a) above? ________________________
c) which species (could be > 1) has as its conjugate base a neutral species? ______________________
and what is the formula of that neutral species? ____________________
d) for which species (could be >1) could we write NEITHER a Ka NOR a Kb? ____________________
Why? ______________________________________________________________________________
Chem 112, Test 1 -- January 21, 2005 -- page 4
FROM THE LAB (28 pts) :
NOTE: In explaining your answers you might find the following description useful: In describing a measurement
value such as 12.345 1 is the “tens” place, 2 is the “units” place, 3 is the “tenths” place, 4 is the “hundredths”
place, 5 is the “thousandths” place
1. A big part of your Lab Zero exercise consisted of your having to add “twenty-five” mL of water by
three different pieces of laboratory equipment available to you: a beaker, a graduated cylinder, and a
pipet
a) When you add the water using your beaker, what value for volume do you write down?
b) When you add the water using your graduated cylinder, what value for volume do you write down?
c) When you add the water using your pipet, what value for volume do you write down?
d) If you wrote down different values, for a) b) and c) above, why did you write “twenty-five” mL
differently? What is the underlying principle at work here that dictates how you write this value?
e) What do we mean when we speak of the quality of a measurement? In the case above, how did you
determine the quality of the measurement for cases a) b) and c)? What values for quality do you get?
2. A second part of the exercise introduced the concept of “Raw” data as contrasted to “Processed” data.
a) What is the distinction between these two?
b) From the Lab Zero exercise, give an example of a piece of raw data, and a piece of processed data.
c) What is the operating principle that governs how you write down a value for a piece of processed
data?
Chem 112, Test 1 -- January 21, 2005 -- page 5
3. Class data for the density of water was compiled, and you were given a printout of this data in two
forms: distribution curves (plots) and tally sheets (tables)
a) A big deal was made about finding the range of values that incorporated 95% of all values. What
does identifying this range entitle you to state about the experimentally-determined density of water?
b) How does the 95% range of mean density values compare to the 95% range for individual density
values? What does this comparison suggest about how to make most effective use of your measurement
data. Explain clearly and concisely.
PROBLEMS (40 pts) SHOW ALL WORK. NO “MAGIC” PERMITTED.
(NOTE: Watch quality of all processed values!)
1. In each case below, Identify the solute species present in solution BEFORE any minor rxn. Then
write the appropriate minor reaction and the appropriate K expression. There are NO major
reactions here and NO calculations are required.
a) 10.0 mL of Benzoic acid, C6H5COOH, is dissolved to a final volume of 100 mL. C6H5COOH has a
Ka value of 6.5x10-5.
b) 30 mL of Concented Ammonia, NH3, is dissolved to a final volume of 250 mL. NH3 has a Kb of
1.8x10-5
c) 15.0 g of Sodium Acetate, NaOAc, is dissolved in water to a final volume of 500 mL. The pKb for
Acetate ion, OAc- , is 9.30
2. Concentrated Nitric Acid, HNO3 (MW = 63.00) comes from the suppliers as a 15.0 M solution.
Suppose you run into a recipe which calls for the use of 350 mL of a 0.60 M solution of Nitric Acid.
a) How much of the concentrated acid, in mL, will you need to prepare the needed solution?
b) How do you go about preparing the solution specified in the recipe? (Be as specific as you can be in
your answer here. A step-by-step recipe is best)
Chem 112, Test 1 -- January 21, 2005 -- page 6
3. The crazy weather we’ve been having has made you sick to your stomach, so you decide to take
some medication for relief. A suggested remedy is Milk of Magnesia, whose active ingredient is
Mg(OH)2 (MW = 58.34). But in your fevered state, you’re wondering what the % by weight of
Mg(OH)2 is in Milk of Magnesia, so you decide to analyze for %Mg(OH)2 by titrating with a HCl titrant
whose concentration has been standardized to a value of 0.1288 M HCl. You carefully weigh out a
sample of Milk of Magnesia whose weight is 0.7620 g and titrate so that complete titration is achieved.
It takes you 44.38 mL of the HCl titrant to get to the equivalence point.
a) Write the reaction which occurs between Titrant and Analyte
b) What is the % Mg(OH)2 in the sample?
4. You perform the one titration above, and you’d like to do replicate determinations for %Mg(OH)2,
but you’ve run out of standardized HCl (MW = 36.50) titrant, and when you approach the Kindly Old
Professor and ask for more, he tells you you’ll have to standardize your own (he’s not very helpful). It
turns out that 4-aminopyridine (MW = 94.12) -- you can abbreviate it as 4-AMP -- is a primary
standard base that reacts with the acidic HCl in a 1:1 molar ratio. You weigh out .4864 g of this dried
primary standard, and you find it takes 45.17 mL to achieve a satisfactory titration for a solution of HCl
which you’ve prepared. What is the molarity of the HCl solution?
Pledge: I have neither given nor received any unacknowledged aid on this test.
Signed: ______________________________