Chapter 14
Experiment: Periodic Properties

 

Purpose: To investigate the periodic variation of density and solubility of compounds.

Background: When the elements are arranged in order of increasing atomic number, they exhibit a periodic recurrence of properties.  This fact led to the grouping of elements on the periodic table.  Elements in vertical columns of the periodic table form GROUPS (also sometimes called families) with similar physical and chemical properties.  These similarities are due, in large part, to the fact that all the elements within a group have the same outer shell electron configuration.  You can also find periodic trends in certain properties, such as density, among the elements within a given group.  In addition, compounds that contain elements from the same group can display trends in properties such as solubility.

In this experiment, you will investigate the variation in density among certain Group IV elements and the variation in solubility for salts of the Group II elements.  You will use your results to predict the density of another Group IV element and to identify an unknown Group II cation.

Materials:

Procedure:

Part A - Densities of the Group IV elements

1. Determine the densities of the Tin, Lead and Silicon samples by using water displacement.  Record on Date Table #1.  Note the appearance of these elements.  Use a 10 mL graduated cylinder and the analytical balance at the front of the room.

2. Completely dry the metals with paper towels and return to the front table in the container indicated "Used Tin" or "Used Lead" or "Used Silicon."  DO NOT DISPOSE OF THE METALS IN THE TRASH NOR DOWN THE SINK DRAIN!!!!!

Part B - Solubilities of Salts of Group II elements

Solutions of barium and strontium salts are EXTREMELY TOXIC!

Solutions of H2SO4 can be EXTREMELY CAUSTIC!

Solutions of K2CrO4 are both TOXIC and CAUSTIC!

  1. Add 20 drops of each of the following solutions to 4 different small test tubes:

  2. Add 20 drops of H2SO4  to EACH tube above to provide sulfate ions for reaction with the Group II metal ions.  A precipitate (solid) is formed when a reaction occurs where one of the products is insoluble - small particles come "out of solution." If the salt listed above is INSOLUBLE in water, a precipitate will be formed.  Record the solubility of each metal sulfate in the Data Table #2.  Use I for "insoluble" and S for "soluble."

  3. Dispose of the solutions or precipitates into the trash can with the liner.   Then, thoroughly clean out your test tubes tap water and then rinse with DISTILLED WATER (in the wash bottles).

  4. Repeat steps 1-3 but this time, use Na2CO3 in place of the H2SO4.

  5. Repeat steps 1-3 but this time, use K2CrO4 in place of the H2SO4.

  6. Test your unknown using the same steps #1-5 above.  

  7. Dispose of the solutions or precipitates into the trash can with the liner.  Then, thoroughly clean out your test tubes with soapy water, RINSE thoroughly and INVERT them into the test tube rack.  Take the test tube rack with clean inverted tubes back up to the front table.

Data Tables:

Copy/paste each of these data tables into separate Microsoft Word documents.  Bring both Data Tables to class on the day of the experiment.

Name:

Block: 

Teacher name: 

Data Table #1 - Densities of Group IV elements
  Silicon
Period 3		 Tin
Period 5		 Lead
Period 6
Appearance

 

      
Starting volume of water alone (mL) - SF!

 

      
Ending volume of water + metal (mL) - SF!

 

      
Volume of metal (mL) - show all setup and include units! - SF!

 

      
Mass of Metal (g) - SF!

 

      
Density of metal (g/mL) - show all setup and include units!  SF!

 

      

 

Name:

Block: 

Teacher name: 

Data Table #2 - Solubilities of Group II elements
S for soluble 
I for Insoluble
   SO4-2 CO3-2 CrO4-2
Mg+2      
Ca+2      
Sr+2      
Ba+2      
unknown      

 

Analysis:

Copy/paste these questions into Microsoft Word and word-process the answers the questions.

1. Be sure your densities of the tin, silicon and lead are correctly calculated in the data table.

2. Graph Density (g/mL) vs. Period Number in Microsoft Excel.  Use the scatter plot function. Be sure to label the x and y axes.  Be sure Period Number is on the x-axis.  LABEL EACH DATA point with the NAME of the metal.  In the upper right of the graph, be sure you have your name and block number.

3. Using YOUR GRAPH you prepared in Excel, determine the density of Germanium (Ge).  HAND DRAW an arrow on your scatter plot indicating where the Germanium point would be (Period 4). Compare your estimate with the accepted density of Germanium (5.5 g/mL).  Calculate the percent error between your estimated value and the accepted value.  Show all work in your answer!.  Remember that....

% error =  | accepted value - estimated value |   x   100
                              accepted value

4. In Part B of the experiment, what type of chemical reaction is occurring for each combination of solutions?  For each pairing, write a balanced chemical equation.  If a product is insoluble, indicate it by UNDERLINING the formula of the precipitate.

5. Describe and explain the relationship that you see in Data Table #2 between the solubility of the Group II ions and their position on the periodic table.

6.  Can you identify your unknown in Data Table #2?  EXPLAIN carefully and thoroughly!

Lab Report:

Staple together in this order and turn in:

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