Chem 112, Test 1 -- January 20, 2006 -- page 1
Name _________________________
You are allowed 1 1/2 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 -- (28 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) On your first real day in lab, you were directed to obtain and dry some “Primary Standard” KHP, for
use in standardizing the NaOH solution you also prepared that day. What is so special about something
being a Primary Standard?
a) Primary Standard KHP permits you to determine the #mmoles of KHP simply by drying and
weighing
b) Primary Standard KHP permits you to determine the #mmoles of KHP to high quality simply by
drying and weighing
c) Primary Standard KHP permits you to determine the #mmoles of KHP without concern for
systematic error simply by drying and weighing
d) Primary Standard KHP permits you to determine the #mmoles of KHP without concern for random
error simply by drying and weighing
2) In your KHP determination instructions you read “. . . accurately (+/- 0.1 mg) weigh by
difference a KHP sample whose ‘target weight’ is 0.7 g . . .”. What does this phrase
mean in terms of what you actually do in lab?
a) Use a tenth-gram balance, since you are given only a 0.7 value. Place the KHP on a piece of
weighing paper on the balance and stop when the balance indicates 0.7g.
b) Use a tenth-gram balance. Tare the weighing bottle+KHP contents to zero. Transfer some
KHP to your titrating flask and re-weigh. Continue process until the balance indicates 0.7 g.
c) Use the analytical balance. Place the KHP on a piece of weighing paper on the balance and
stop when the balance indicates a “7“ in the tenths-place of the balance. Record all 4
decimal places.
d) Use the analytical balance. Tare the weighing bottle+KHP contents to zero. Transfer some KHP to
your titrating flask and re-weigh. Continue process until the balance indicates a “7“ in the
tenths-place. Record all 4 decimal places.
3) Given a mixture of bulk Sodium Sulfate, Na2SO4, and bulk sugar, C6H12O6, which of the following
represents accurately the ultimate units present in these two compounds?
a) Na2SO4 and C6H12O6 molecules
b) Na+ and SO42- ions, C6H12O6 molecules
c) Na+ and SO42- ions, 6 C, 12 H, and 6 O atoms
d) Na22+ and SO42- ions, C6H12O6 molecules
e) Na2SO4 molecules, 6 C, 12 H, and 6 O atoms
4) We say a titration is a major reaction, yet we say it is a special major reaction. What is so special
about a titration?
a) It can only occur when the reactants are added very slowly
b) It ends up with no reactant being the limiting reagent
c) It ends up with only 1 reactant being the limiting reagent
d) It ends up with 2 reactants being limiting reagents
e) 2 of the above
Chem 112, Test 1 -- January 20, 2006 -- page 2
5) We pointed out that the distribution curve obtained in the Lab Zero experiment indicated the
presence of systematic error. What is the most likely physical cause by which systematic error
was introduced?
a) the failure to improperly level or to check the level status of the balance used.
b) a failure to properly tare the balance
c) the use of To Contain volumetric glassware
d) the lack of laboratory experience; were the whole lab to be repeated, most likely it would have gone
away, because of increased experience and care on the part of the people making the
measurements.
6) The case of a student using the “wrong” KHP bottle when standardizing the NaOH titrant is a
dramatic example of which type of error?
a) random error
b) gross error
c) systematic error
d) a mixture of gross and random errors
7) In this course we have made an issue to introduce the concept of an “ultimate unit”. Which of the
following questions does this concept best address?
a) Is/are the independent species in solution the same as the bulk formula?
b) Ultimately, does the bulk formula dissolve in water?
c) Is the bulk formula Ionic or Covalent?
d) Ultimately, does the bulk formula possess acid/base properties?
8) We say that the use of a mean of replicate measurements is “better” than using any of the individual
measurements themselves. What do we mean by “better”?
a) The mean is less affected by systematic error
b) The mean will have associated with it a smaller confidence interval
c) The mean will be entitled to have more significant figures attributed to it.
d) If you could make all possible measurements, you would be guaranteed that the mean would be equal
to the True Value.
e) All of the above
f) 2 of the above
9) What is it that we point to for evidence that a Minor Reaction is a Dynamic System?
a) the fact that Minor Reactions produce very little products compared to amounts of reactants
b) the fact that Le Chatelier’s Principle can be made to work
c) the fact that Minor Reactions have associated with them a heat effect
d) the fact that Minor Reactions have associated with them a Keq value
e) the fact that some special Minor Reactions have associated with them special K values.
10) Of the following ions, which could NOT be a base?
a) PO43- b) NH3 c) HCO3- d) H2O e) NH4+ f) they could all qualify to act as a base
11) We all know that a perfectly neutral solution is one whose pH value = 7.00. Which of the
following K’s is most responsible for that fact?:
a) Ka b) Kb c) Kw d) a and c e) none; neutral is unrelated to any K expression
Chem 112, Test 1 -- January 20, 2006 -- page 3
12) 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
13) 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
14) In the KHP determination, which is to be achieved by a Titration, what is the analyte?
a) NaOH
b) KHP
c) the OH- ion
d) the HP- ion
FUNDAMENTALS (55 pts): Short answers. Be precise and concise
1. Define what distinguishes, ultimately, a measurement from the number used to describe it.
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. Write down the bulk formula of an acid which has no conjugate base: _________________________
5. 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? __________________________
6. If pH = 7.12, what is: [H3O+]? ____________ ; [OH-] ? _____________ pOH? ______________
Chem 112, Test 1 -- January 20, 2006 -- page 4
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: PO43- , H2AsO4 -, H2CO3 , CH3NH3+, HNO3
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 its/their formula? ____________________
d) which species (could be > 1) has as its conjugate acid a neutral species? ______________________
and what is its/their formula? ____________________
e) for which species (could be >1) could we write NEITHER a Ka NOR a Kb? ____________________
Why? ______________________________________________________________________________
f) which species has ONLY a Kb? _________________________________
10. What is the distinction between a raw measurement and a processed measurement? Give
an example of each from Lab Zero.
11. Given the generic chemical reaction: aA + bB  cC + dD
a) write the expression implied by the symbol Keq, the equilibrium constant
b) Write the expression implied by the symbol Q, the reaction quotient
c) Explain (an example would help) how Keq, Q, and the Principle of Le Chatlier are interrelated.
Chem 112, Test 1 -- January 20, 2006 -- page 5
PROBLEMS (17 pts) SHOW ALL WORK. NO “MAGIC” PERMITTED.
(NOTE: Watch quality of all processed values!)
1. Given 5.00 mL of a solution of KCl (MW = 74.50) whose concentration is 0.015M.
a) Calculate the number of mg of K+ (AW = 39.00) present in the solution
2. Your lab instructions tell to you to prepare your hydroxide titrant using the 50% (wt/wt)
solution of NaOH (MW = 40.00, density = 1.525 g/mL) available. We also have on hand some
concentrated KOH (MW = 56.00, density = 1.456 g/mL), whose purity is given as 45% (wt/wt).
It too can be used to prepare a hydroxide titrant, as it is also a strong base.
a) What is the Molarity of this concentrated 45% (wt/wt) KOH solution? NOTE: in this work,
the stated % of each of these two concentrated solutions is NOT a number; this stuff is made
up this way.
b) How much, in mL, of this solution would be needed to prepare two liters of hydroxide
titrant solution, where the target concentration is the same as in the NaOH case, ideally tenth
molar?
3. The battery acid in your car battery is actually Sulfuric Acid, H2SO4 (MW = 98.00), a strong acid
with two titratable protons. Suppose you wish to determine the % H2SO4 by weight in your battery
fluid. You carefully remove some battery fluid and weigh it on an analytical balance, obtaining a value
of 4.3591 g. When you titrate this with a 0.2017 M NaOH (MW = 40.00) titrant, you find that you need
44.78 mL to completely titrate the sulfuric acid. What is the % H2SO4 in the battery fluid?
Pledge: I have neither given nor received any unacknowledged aid on this test.
Signed: ______________________________