(Answered)-Chemistry 113.1 Introduction to Chemical Techniques Experiments - (2025 Updated Original AI-Free Solution

Question

?

Hello

(Please read attached lab manual)

(My work is attached in an excel sheet for both trials 1 & 2)

I need assistance with this lab . Within my trials in this lab (Trial 1 / Trial 2) , I find that my Molarity?s for Trial 1 and Trial 2 and significantly different. In regards to the first trial my lab partner did the math so I don?t have his work to show you. But for the second trial you will find my math calculations below.

Please answer the following :

1.Moles FAS ?

2.Molarity FAS

3. Moles of KMnO4

4. Molarity of KMnO4

5. ?Could a solution of iron(III) be titrated with potassium permanganate? Explain.

6. What is the average concentration of the potassium permanganate solution?

Trial 2 Work / Calculations

Moles of FAS = given mass/molecular mass= 4.01/ 392.1388 = 1.02*10^-2 moles

Molarity of FAS = number of moles/volume(liter) = 1.02 *10^-2 moles/(25/1000) ?Molarity = 0.408 M
Chemistry 113.1
Introduction to Chemical Techniques
Experiments 9/10. Standard Solutions

(June 2012)

I. INTRODUCTION
A standard solution is a solution of known concentration that is prepared using exacting
techniques to ensure that the molarity is known to high accuracy. A stock solution is a large
volume of a common reagent prepared to perhaps 1 or 2 significant figures of accuracy. The
approximately 0.10 M NaOH and 0.020 M potassium permanganate solutions are such stock
solutions. You will determine their more exact concentrations by performing a standardization
for each. The reason this is necessary is that many common reagents decay over time or are
hygroscopic and collect additional water. Thus, in many common reagents, the concentration
changes as a function of time. For this reason, most standard solutions are prepared when
needed and only kept a short period of time (i.e., one to two weeks) before being re-standardized.
Once a solution is standardized, then this solution can be used to quantitatively measure the
amount of chemicals in other solutions, as long as these chemicals will react with the standard.
The first method for preparing standard solutions is to use solids that are very stable in air.
Because of the high stability, these salts can be weighed on a balance without fear that the salt
will gain or lose mass (because of oxidation by the oxygen in air or because of the absorbtion or
loss of water from/to the air). The second method for preparing standard solutions is to prepare a
solution and then react this solution with a separate standard solution.
In this experiment, you will use the first method to prepare standard solutions of potassium
hydrogen phthalate (Week 1) and ferrous ammonium sulfate hexahydrate (Week 2). You will
then use the acid/base reaction between potassium hydrogen phthalate and sodium hydroxide to
standardize the approximately 0.10 M sodium hydroxide stock solution (Week 1), and the
oxidation/reduction reaction between ferrous ammonium sulfate and potassium permanganate to
standardize the approximately 0.020 M potassium permanganate stock solution (Week 2). The
reason why solid sodium hydroxide cannot be used to prepare a standard solution via the first
method is that sodium hydroxide is extremely hygroscopic and, therefore, readily absorbs water
from the air. It also reacts with carbon dioxide in the air and cannot be stored for significant
periods of time. Solid potassium permanganate cannot be used to prepare a standard solution
because it is a strong oxidizer that reacts with any trace organic compounds in the deionized
water. Thus, since the concentration of the permanganate ion will change during these side
reactions, the final amount of permanganate in solution will not be known. Thus, stock solutions
of sodium hydroxide solutions and potassium permanganate solutions must be standardized
using the second standardization method.

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Chemistry 113.1
Introduction to Chemical Techniques
Experiments 9/10. Standard Solutions

EXPERIMENT 10A. PREPARATION
SULFATE (FAS) SOLUTION .

(June 2012)

OF A STANDARD FERROUS AMMONIUM

Ferrous ammonium sulfate hexahydrate (FAS, FeSO4(NH4)2SO4 ? 6 H2O) is an iron(II) salt that
is more stable than iron(II) sulfate. Iron(II) is easily oxidized to iron(III) in the presence of
oxygen via
4 Fe2+ (aq) + O2 (g) + (4 + 2 x) H2O ? 2 Fe2O3 ? x H2O (aq) + 8 H+ (aq) .
However, the ammonium ion in FAS is slightly acidic and, therefore, adds H+ to the solution.
The presence of H+ shifts the equilibrium to the left, stabilizing iron(II) in solution with respect
to oxidation. Similar to KHP, FAS has a high molar mass, which allows for high precision when
determining the number of moles in a solution of low volume. Thus, FAS is commonly used to
create standard solutions for oxidation/reduction reactions.
1. Obtain a 100.0 mL volumetric flask from the stockroom. Again, clean this flask
following the procedures given for the preparation of the KHP standard.
2. Weigh 4 grams (3.9 to 4.1 g) of FAS, using a tared, clean dry beaker. Record the exact
weight of FAS in your notebook.
3. Add 25 mL of distilled water to the beaker to begin to dissolve the FAS. Then transfer
the FAS to the volumetric flask, being careful not to spill any of the solution.
4. Rinse the beaker with two 10 mL aliquots of distilled water and a third 10 mL aliquot of
3M sulfuric acid to stabilize the solution. Add these washings to the volumetric flask
(again being careful not to spill any of the solution.) This ensures that any FAS adhering
to the walls of the beaker is transferred to the volumetric flask.
5. Close the flask with the lid (or a rubber stopper or parafilm) and invert several times to
mix the contents. Continue this process until such time as the FAS is completely
dissolved.
6. Remove the lid (or rubber stopper or parafilm) and rinse with a small amount of distilled
water, again making sure that the water drops into the volumetric flask.
7. Add enough distilled water to nearly fill the flask to the etched line, cover, and invert
several times to mix the contents. Remove the flask cover, again rinsing to ensure that all
of the solution remains in the volumetric flask.
8. Add water with a clean medicine dropper (or pipette) to bring the bottom of the meniscus
to the etched line. Show your laboratory instructor your volumetric flask once you have
completed the preparation of the solution. If you have overfilled your flask, you will
need to begin again !
9. The laboratory instructor must sign the laboratory notebook next to the recorded volume
to verify that the volumetric flask was filled correctly.
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Chemistry 113.1
Introduction to Chemical Techniques
Experiments 9/10. Standard Solutions

(June 2012)

EXPERIMENT 10B. STANDARDIZATION OF POTASSIUM PERMANGANATE.
PERFORM

THIS EXPERIMENT IN PAIRS.

EACH

PAIR SHOULD DO TWO TRIALS, WITH EACH

STUDENT IN THE PAIR DOING ONE OF THE TRIALS.
IS DONE BY WHICH STUDENT.

EVERY

RECORD IN THE NOTEBOOK WHICH TRIAL

STUDENT SHOULD COMPLETE A SINGLE TITRATION IN

30 MINUTES OR LESS. IF TIME ALLOWS PERFORM A THIRD TITRATION.
Oxidation/reduction reactions are chemical reactions that lead to a change in the oxidation
numbers of species in the reaction. In this experiment, you will perform a redox titration to
standardize the potassium permanganate solution. In this titration, aqueous iron(II) reacts with
the aqueous permanganate ion (dark red in water) in an acidic solution to give iron(III) and
aqueous manganese(II). You should balance this chemical reaction before coming to the
laboratory.
1. Carefully clean the two burettes and rinse several times with distilled water.
2. Once the burette is clean, rinse the burette with three 10 mL portions of the solution that
the burette will hold (one burette will hold the approximately 0.02 M stock potassium
permanganate solution [obtain about 100 mL ] to be standardized, and one will hold the
standard FAS solution), again allowing some of the solution to run through the tip.
Discard the rinsings in the appropriate waste bottle. Note: At least one of your
burettes will have white numbering and markers. This is the burette that must be
used for potassium permanganate.
3. Make sure that the stopcock is closed. Hold the burette with its top below eye level and
fill it with solution to somewhere near the top mark. Run a little solution out of the
bottom and watch for air bubbles in the tip. (To remove a bubble, hold the partly filled
burette in a nearly horizontal position, open the stopcock part way and allow the slow
flow of liquid to push the bubble out of the tip.)
4. Clamp the filled burette in a vertical position and record the initial volume of liquid in
each burette. Always wait at least 15 seconds before taking a volume reading to ensure
that the liquid has drained down the inner surface of the burette.
5. Use the burette containing the standard FAS solution to place approximately 25 mL of
the FAS solution into a clean Erlenmeyer flask. Record the actual volume of FAS
solution used in your laboratory notebook. Carefully and slowly add approximately 15
mL of 3 M sulfuric acid to the 25 mL FAS sample in the Ehrlenmeyer flask.. This acid
provides the H+ ions necessary for the oxdidation/reduction reaction.
6. Place the Erlenmeyer flask on a sheet of white paper under the burette containing the
potassium permanganate solution. (The white paper will help in seeing the end point.)
7. Begin adding potassium permanganate to the FAS solution, Swirling the flask gently and
steadily to mix the solution thoroughly. One can begin to add potassium permanganate in
1 - 2 mL portions. Initially, transient red streaks will appear as potassium permanganate
is added and reacts with iron(II). As the titration continues, the red color will persist for
longer intervals, but continue to disappear. As this happens, begin to add potassium
permanganate in smaller portions. The longer the red color persists, the smaller the
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Chemistry 113.1
Introduction to Chemical Techniques
Experiments 9/10. Standard Solutions

(June 2012)

amount of potassium permanganate should be added. As you get closer to the
equivalence point, potassium permanganate should be added dropwise.
13. The equivalence point is marked by the first permanent faint pink/red color in the FAS
solution. (Permanent is a color change that persists for at least 30 seconds.) If potassium
permanganate has splashed onto the walls of the Erlenmeyer flask or any drop hangs
from the burette tip, when you are near the equivalence point, wash these down into
solution using distilled water from your wash bottle. Show your end point color (i.e. the
flask) to your instructor before continuing.
8. If your instructor indicates that you have overshot the equivalence point (i.e., the color of
the solution is dark pink or red/purple), add FAS solution from the FAS burette dropwise
until the color disappears. Then add potassium permanganate from the other burette
dropwise until you have reached the equivalence point. Be sure to record both the
volume of FAS added and the volume of potassium permanganate added.
9. Obtain a new clean Erlenmeyer. Refill the burettes and repeat the titration with an
additional volume of FAS.
Once the two titrations have been completed, record your calculated value for the molarity (M)
of the potassium permanganate solution in your laboratory notebook.
The FAS solution can be discarded in the appropriate waste container. The burettes can also be
emptied and rinsed with three 10 mL portions of distilled water. Both volumetric flasks should
be cleaned with distilled water and returned to the Stockroom.

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