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Formal Report - Experiment 9

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					Experiment # 9: Chemical Equilibrium                                         MAB2, Group # 9, Ma’am Leah Rubio
GENTOLIA, Michal Consuela C.                                                                    March 22, 2010
TORREMANA, Cyrille Stephanie J.

                                                     Abstract

         Chemical equilibrium is the state reached by a certain reaction mixture when the rates of forward and
backward reaction have become equal. In dynamic equilibrium the forward and backwards reactions continue at
equal rates so the overall effect does not change. On a molecular scale there is continuous change. On the
macroscopic scale nothing appears to be happening. The system needs to be closed – isolated from the outside
world. Nothing can be added to the system or taken away from it apart from energy. It is very important to be
knowledgeable about this topic since it is vital for these reactions and mixtures to maintain equilibrium at all
times. There are applications of chemical equilibrium in real-life, and these are vital as well. In Experiment No. 9,
different reagents were added to the Fe(NO3)3 and KCNS mixture. There were five reagents that were added
namely 0.1 M Fe(NO3)3, 0.1 M KCNS, 0.1 M KCl, 0.1 M AgNO3 and NaF crystals. Distilled water was also added
to the mixture to serve as a reference to the latter mixtures. The change in temperature was also executed when
two test tubes were subjected to heat and ice separately. The effects were observed to see whether there has
been a forward or a backward shift under different conditions.


Keywords: shift, equilibrium, pressure, temperature, concentration, system


Introduction                                                  means of food preservation that do not involve
                                                              changes in temperature, maintains chemical
         A chemical reaction is in equilibrium when           equilibrium in the foods and thereby prevents or at
there is no tendency for the quantities of reactants          least retards spoilage. Even more important is the
and products to change. If there have been                    maintenance of equilibrium in reactions between
observable changes taking place like change in                hemoglobin and oxygen in human blood.
color, release of gas bubbles, appearance of
precipitate, or even the release of heat, one should
bear in mind that the reaction is not yet at                  Experimental
equilibrium. Though this is the case, one should
also note that it doesn’t necessarily mean that the                    For this experiment, we used the following
reaction is at equilibrium if there is no apparent            apparatus: 10 mm x 100 mm Test Tubes, 100-mL
change. The equilibrium state is one in which no              beakers, spot plates and alcohol lamps. We also
change in composition take place, and no energetic            used the following reagents: 0.1M Fe(NO3)3, 0.1M
tendency is present for further change.                       KCNS, 0.1M KCl, 0.1M AgNO3. We also used NaF
                                                              crystals and ice water.
        The Le Chatelier’s Principle states that
when a system in equilibrium is disturbed by a                         We combined 20 drops of 1 M Fe(NO3)3
change of temperature, pressure, or concentration             with 20 drops of 1 M KCNS solutions in a test tube.
variable, the system shifts in equilibrium                    Having this solution, we placed 10 drops of it to the
composition in a way that tends to counteract this            six spots in the spot plate. On the first spot, we
change of variable                                            added another 10 drops of distilled water which
                                                              served as the reference. We added 5 drops each of
         The addition of reagents in this experiment          0.1 M Fe(NO3)3 to the second spot, 0.1 M KCNS to
serves as the bombardment in the reaction that is             the third spot, 0.1 M KCl to the fourth spot, 0.1 M
already been in an equilibrium state. The changes             AgNO3 to the fifth spot and a pinch of NaF crystals
that will arise from this will be able to help in             to the sixth spot.
determining the shift.
                                                                      In two separate test tubes labeled as test
       Chemical equilibrium is very vital and                 tube 7 & 8, we added ten drops of distilled water.
observable with issues concerning human health.               Ice water was prepared on a 50-ml beaker where
The cooling of food with refrigerators, along with            test tube 7 was placed. After dipping test tube 7, it

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Chem 14.1, Chemical Equilibrium
was compared to the solution in the first spot. On               After adding 5 drops of 0.1 M KCl, the
the other hand, test tube 8 was heated over low         solution had white precipitate and was yellowish in
flame. It was also compared to test tube 1              color. The solution became oil-like and eventually
immediately after heating.                              turned to white upon the addition of the NaF
                                                        crystals.
         These processes allowed us to determine
the directions of shift for each reaction.                       After dipping test tube 7 in the prepared ice
                                                        water, the color we observed was lighter than the
                                                        reference’s color. However, it should be darker than
Result                                                  the reference’s color.

  REAGENT /                                DIRECTION             When test tube 8 was compared to the
                    OBSERVATION
 TREATMENT                                  OF SHIFT    reference after heating, there was no significant
0.1        M        Darker                Forward       change except for the appearance of bubbles.
Fe(NO3)3                                                However, the color should be lighter than the color
0.1 M KCNS          Super Darker          Forward       of the reference.
0.1 M KCl           Red                   No shift
                    * No change                                There are conditions that affect the balance
0.1 M AgNO3         White                 Backward      of the equilibrium – Pressure, Temperature and
                    precipitate and                     Concentration.
                    yellowish        in
                    color                                        If the pressure is increased, the equilibrium
Pinch of NaF        “Oil-like” at first   Backward      will shift to reduce the pressure, meaning it will
                     Clear                             move to the side with the least number of gaseous
Increase       in   Lighter               Forward       moles. On the other hand, if the pressure is
Temp                * Darker                            decreased, the equilibrium will move in the direction
Decrease       in   Appearance of         Backward      that increases the number of gaseous moles.
Temp                Bubbles         
                    SAME                                        If there is a forward increase in
                    * Lighter                           temperature, the reaction is exothermic. On the
                                                        other hand, if there is a backward decrease in
                                                        temperature, the reaction is endothermic. In
Discussion                                              summary, high temperature is equated to lots of
                                                        reactant while low temperature is equated to lots of
         After adding distilled water to the Fe(NO3)3   products.
and KCNS solution, the color of the mixture became
light red orange. This served as the reference for              By adding one of the ingredients that go to
the comparison of color of the succeeding solutions.    make up the reaction, the concentration changes,
                                                        thus making the equilibrium act to shift reaction
        Five other reagents were added separately       such that the amount of added material is reduced.
to the Fe(NO3)3 and KCNS solution.
                                                               Adding a catalyst in a reaction does not
         When the 0.1M Fe(NO3)3 was added, the          make any difference to the position of equilibrium,
color of the mixture became darker compared to          and Le Chatelier's Principle doesn't apply to them.
that of the reference mixture.

      When 0.1M KCNS was added, the mixture             Guide Questions & Answers
was very darker than that of the reference. It
seemed blackish or dark bluish.                             1. Explain your observations on the basis of
                                                               Le Chatelier’s Principle.
         The solution turned red when there was an
addition of 0.1M KCl. However, there should have                Le Chatelier’s principle states that if a
been no change in color compared to the reference               dynamic equilibrium is disturbed by
mixture.                                                        changing the conditions, the position of
                                                                equilibrium moves to counteract the
                                                                change. The experiment, based on this
                                                                                                 Page 2 of 3

Chem 14.1, Chemical Equilibrium
        principle, has undergone a lot of changes in       References
        condition which explains the change in the
        shifts of the reactions. Upon addition of          (n.d.) Chemical equilibrium. Retrieved March 12,
        reagents, there were visible changes in the        2010                                             from
        color of Fe(NO3)3, KCNS, AgNO3, and NaF            http://library.thinkquest.org/10429/low/equil/equbod
        because there was a change in the                  y.htm
        concentration. Having the ice water and the
        addition of heat, there were also                  (n.d.) Chemical equilibria. Retrieved March 14,
        remarkable changes in their colors which           2010                                         from
        explains the change in temperature that isa        http://www.webchem.net/notes/how_far/equilibria/c
        based on Le Chatelier’s principle.                 hemical_equilibria.htm

    2. Which species (ions) in the added reagents          Clark, Jim. (2002). Le Chatelier’s principle.
       are effective in altering the state of the          Retrieved     March      13,      2010         from
       system?                                             http://www.chemguide.co.uk/physical/equilibria/lech
                                                           atelier.html
        There were four reagents that had
        observable shifts. These are NaF, AgNO3,           Clark, Jim. (2002). An introduction to chemical
        KCNS and Fe(NO3)3. In the case of NaF,             equilibria. Retrieved March 13, 2010 from
        since both are not present in the given            http://www.chemguide.co.uk/physical/equilibria/intro
        mixture, sodium and fluorine ions contribute       duction.html#top
        in altering the state of the system. For
        AgNO3, silver has caused the shift to occur.       Lower, S. (2010, Jan. 7). Chemical equilibrium
        In the case of the two other reagents, they        introduction: Reaction that goes both ways.
        have also caused the alteration because of         Retrieved      March     12,     2010     from
        the additional moles since they are also           http://www.chem1.com/acad/webtext/chemeq/Eq-
        present in the given mixture.                      01.html#SEC2

    3. Is the reaction endothermic or exothermic?
       Why?

        With the addition of heat, there is visible        I hereby certify that I have given substantial
        increase in temperature and notable                contribution to this report.
        change in the color of the solution,
        therefore, the reaction is exothermic.

                                                           GENTOLIA, Michal Consuela C.
Conclusion & Recommendations

        Based on the data gathered from the
experiment,     we     therefore     conclude       that   TORREMANA, Cyrille Stephanie J.
concentration, pressure and temperature are
factors that contribute in the shift of direction that
will enable the mixture to go back to its equilibrium.

         Some of our observations are different from
that of what should have been observed, especially
during the part wherein temperature has been
changed. We recommend that those who will be
conducting this experiment should be vigilant
enough that they try to follow the procedures as
keen as possible. The deviations from the
theoretical results might have been caused by
some errors during the experiment itself.


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Chem 14.1, Chemical Equilibrium

				
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