lab---activity-series

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					                             Lab - Exploring an Activity Series
Introduction
We will explore the relative reactivities of several metals in particular chemical reactions. First,
you will explore the reactions of different metals with two different acids. Metals will often
react with acid in the following type of reaction:
                         M(s) + H3O+(aq)  Mn+(aq) + H2(g) + H2O(l)
(This equation obviously cannot be balanced until we know the identity of the metal.) All metals
do not react with all acids. Which do and which don’t is what you will be investigating.

The other reaction you will explore is a replacement reaction. For example, if you place copper
metal in a solution of silver nitrate, the copper ion will replace the silver ion in solution:
                        Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)
What you would observe is the silver metal precipitating on the copper, either as a silvery or
black solid. You would also observe the solution turning from colorless (because Ag+(aq) is
colorless) to blue (because Cu2+(aq) is blue). The nitrate ion (NO3) is not really involved in the
chemical reaction and is acting merely as a spectator ion. If we simply write the net ionic
equation, it would look like this:
                             Cu(s) + 2Ag+ (aq)  Cu2+ (aq) + 2Ag(s)
This type of reaction is often called a single replacement reaction.

An activity series is a listing of metals according to their reactivity, typically as reducing agents.
That is, the more active a metal is in its elemental (uncombined) state, the more likely it is to
donate electrons to a positive ion (cation) in solution, and thus replace it in solution. In the
reaction above, the copper is more active than silver and thus replaces silver ions in solution.

You will be reacting five (5) unknown metals with acids and with solutions containing the
cations of these metals. From your observations, you will be able to rank the metals in order of
reactivity. From this ranking, you might be able to come up with the identity of the metals.


Pre-lab Assignment
   1. Prepare your notebook for this experiment. Make tables that you can fill out while
       performing the procedure. You will be attempting a large number of reactions in this
       experiment, and it is very important that you stay organized. You should make sure to
       leave plenty of room to record your observations.
   2. The following results, displayed in a table on the next page, were obtained through a
       series of two experiments:
           a. Write net ionic equations that describe all of the results noted from Experiment 1
               and Experiment 2.
           b. Explain the color change observed in Experiment 2 (replacement reactions).
           c. Briefly discuss the relative activities of silver and chromium.




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Experiment 1: Reactions with acids:

                                             Cr(s)                         Ag(s)
                       HCl              metal dissolves,                no apparent
                                        bubbles, green                   reaction
                                           solution
                       H2SO4            metal dissolves,                no apparent
                                        bubbles, bluish                  reaction
                                        purple solution

Experiment 2: Replacement reactions:
Cr 3+ + Ag metal: no apparent reaction, silver metal did not
change, solution stayed green.
Ag + + Cr metal: silvery solid formed on piece of Cr metal. Solution
went from colorless to bluish-green.

Procedure
Although the instructions below make it sound as if you should do everything at once, it is best if
you perform each reaction separately, so as to make careful and thorough observations. Some of
the metals may have coatings of metal oxide on the outside. Try to expose a fresh metal surface
to each of the metals by using sandpaper or steel wool to scour the surface of the metal. You can
also use the heavy end of a utility clamp to “mash” the metal and expose a fresh surface.

Part I. Reaction of different metals with different acids:

Obtain a laminated reaction sheet for the ACID REACTIONS from the reagent bench. Place a
small piece of each of five (5) unknown metals in each of the squares in the appropriate column.
Record the appearance of each metal in your notebook, including reference to the presence of
metal oxides. Cover each piece of metal with a few drops of the solution indicated in the matrix
below and make careful observations. Note any reaction that seems to be occurring: color
change, gas bubbles forming, etc. After you have completed your observations, wipe the sheet
into the waste container provided and thorough rinse and dry it.

                Caution: HCl and H2SO4 are corrosive acids. If either comes in contact
                with your skin, rinse the area immediately with copious amounts of water.

                               Matrix for reactions of metals with water and HCl:

                           A            B             C             D               E
         Water
         3 M HCl
         6 M HCl
         3 M H2SO4
         6 M H2SO4
If you obtain any ambiguous results, keep in mind that some of the metals may be coated by a
layer of metal oxide (MxOy), which protects the metal surface from reacting with the acid. You



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may wish to repeat some of the reactions above, first ensuring that you have a fresh metal surface
exposed.

Part II. Replacement Reactions:

Obtain a laminated sheet for the REPLACEMENT REACTIONS from the reagent bench. You
will notice that the grid titles are left blank. It is your job to design an easy procedure to test the
reactivities of the metals with the solutions of the metal salts. You will be given 1 M solutions of
each metal salt. Carefully read the labels, their may be hints to the metals identity in the
formula...

Record your procedure in your lab book. Record your observations in a data chart in your lab
notebook.

Report

        Title
        Background
        Purpose
        Procedure (as followed in Lab)
        Summary of data in the form of tables which should provide information about:
            whether a reaction occurred,
            the evidence for or against reaction occurring.
            If a reaction did occur, you should write the net ionic reactions (using the fictitious
               symbols like A or A3+).
            You should also include any observations you made regarding the presence of
               metal oxides.
        Conclusion: Include a rank the metals in order of reactivity with supporting lines of
         evidence. Discuss any relationship between the activity of a metal and its tendency to
         form metal oxides.




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