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 as seen in the periodic table. Elements in vertical columns of the periodic table form groups (famines) 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 the densities and solubility of compounds that contain elements in the same group.

In this experiment, you will investigate the periodic variation of density and solubility of compounds within groups. More specifically, you will determine the densities of certain Group 4A elements and the solubilities of certain salts of Group 2A elements. Using your results, you will predict the densities of other Group 4A elements and the solubility of an unknown Group 2A salt.

Goals

• Measure the densities of certain elements in Group 4A.
• Measure the solubilities of certain salts of Group 2A elements.
• Describe the periodic variation of the density and solubility of compounds.
• Predict the densities of untested Group 4A elements
• Predict the solubility of an unknown Group 2A salt.

Equipment
 
 
 

Safety goggles	1 plastic wash bottle
8 centigram balances/class	1 50-mL graduated cylinder
4 small test tubes or 1 spot plate	1 dropper pipette
1 test-tube rack

Safety

• Note the Safety Symbols used here and in the Procedure section. Review safety information on pages 7-10.
• Always wear safety goggles when working in the lab.
• A number of the chemicals used in this experiment are toxic and/or irritating to the skin. Avoid skin contact with these chemicals.
• Sulfuric acid is corrosive and can cause severe burns.
• Wash your hands thoroughly after completing this experiment.

Copy Tables 23.1 and 23.2 into your laboratory notebook. As you perform the experiment, record your data in these tables.

Part A. Densities of Group 4A Elements

1. Determine the densities of the tin (Sn), lead (Pb), and silicon (Si) samples by water displacement method described in Experiment 4. Record the data in Table 23.1. Note the appearance of these elements.

 

 
 
 
 
 
 
 
 
 
 
 

Part B. Solubilities of Salts of Group 2A Elements

2. CAUTION: Salts of barium and strontium are extremely toxic. Add 1 ml (20 drops) of Mg(NO₃)₂ solution to a small test tube. Add 1 ml of Ca(NO₃)₂ solution to a second test tube, 1 ml of Sr(NO₃)₂ solution to a third, and 1 ml of Ba(NO₃)₂ solution to a fourth.
3. CATUION: At a concentration of 1M, sulfuring acid, H₂SO₄ is a severe skin irritant. Add 1 ml (20 drops) of 1M H₂SO₄ to each tube to provide sulfate ions for reaction with the Group 2A metal ions. If the salt (Mg SO₄, Ca SO₄, SrSO₄, or BaSO₄) is insoluble in water, a precipitate will be formed. Record the solubility of each metal sulfate slat in Table 23.2 using the following letter codes: S = soluble, I = insoluble.
4. Dispose of the materials in the test tubes as directed by your teacher. Rinse the test tubes with distilled water and dispose of the rinse water as directed by your teacher.
5. Repeat step 2, then repeat step 3 using 1M Na₂CO₃ in place of 1M H₂SO₄.
6. Repeat step 4
7. CATUION: Chromates are both toxic and irritating. Repeat step 2, then repeat step 3 using 1M K₂CrO₄ in place of 1M H₂SO₄.
8. Repeat step 4
9. Obtain an unknown salt solution from your teacher. The solution will contain ions of a Group 2A metal. Perform the solubility test you identify the unknown ion. Treat the unknown as if it were toxic and irritating.
10. Dispose of the materials as directed by your teacher.

Note, one page of graph paper is required for your report.

1. Calculate and record the densities of the tin, silicon, and lead samples in Table 23.1
2. Prepare a graph of densities versus period number for tin, silicon, and lead.

1. Based on your graph, estimated the density of germanium, Ge. Compare your estimate with the accepted density of germanium (5.46 g/cm³) Give any possible sources of any error.
2. Calculate the percent error between your estimated value and the accepted value for the density of germanium.

percent error =

[accepted value - estimated value] Accepted Value

x  100 percent

3. Describe any relationship that you see in Table 23.2, between the solubility of salts containing alkaline earth metal ions and the position of the metals in the periodic table.
4. Based on the data in Table 23.2, you may not have been able to identify your unknown specifically. Explain.

1. Construct data tables for (a) the elements in Group 1A and (b) the elements in Period 3. In the tables, include information on the following physical properties; melting points, boiling point, density, hardness, electron conductivity, physical state, and appearance. Do you see any evidence of periodic trends? If so, describe them.
2. Choose three properties, other than those in the preceding question, that demonstrate periodic trends within groups 1A and 2A. Include elements with atomic number up to 56. Plot on the same graph the values of properties for both Group 1A and Group 2A. Comment on the results.