Mendeleev arranged the elements in the Periodic Table in order of increasing atomic number in horizontal rows so that elements with similar properties recur periodically (another words they fall directly beneath each other in the Table). The elements in a given vertical column are referred to as a family or group. The physical and chemical properties of the elements in a given family change gradually as one goes from one element in the column to the next. By observing the trends in properties, the elements can be arranged in the order in which they appear in the Periodic Table.
Procedure
I. activity series
CAUTION: Sodium and potassium react very rapidly with water to evolve hydrogen and heat. This is potentially dangerous because of the possibility of the violent explosive reaction of H
2
(g) with O
2
(g) present in the air. Both sodium and potassium cause severe chemical burns when it comes into contact with the skin.
CAUTION:
H
2
is flammable.
Demo : The reactions of sodium and potassium with water will be demonstrated for you. Observe the rate of evolution of H
2 gas as a tiny piece of sodium or potassium is placed in a 500-mL beaker full of deionized water. Record your observations on your report form and write a balanced equation for these reactions.
- Place 5 mL H
2 O (cold water should be used for Cu, Zn and Ca and warm water should be used with Mg) in each of four clean test tubes and place them in a test tube rack. Label them as follows:
- Place several small pieces of Mg, Cu, and Zn in the correctly labeled test tube prepared above. Place
two or three pieces of Ca turnings in the test tube labeled "Ca".
- Watch for evidence of reaction by noting evolution of gas bubbles and any change in the color or size of the metal. Be patient, some reactions may be slow! Record your observations and write net ionic equations for each reaction.
-
Discard the Ca and water in the Ca recovery beaker . Decant the water out of the test tubes containing Mg, Cu, and Zn and leave the pieces of metal that remain unreacted in each test tube.
Note: Trapped air bubbles on the metal surfaces are not indicative of a reaction.
Note: Net ionic equations must balance in mass (atoms) and in total charge on each side of the equation.
Caution: this part of the procedure must be done in a fume hood!!
CAUTION: Some of the test tubes may become very hot. Leave them in the test-tube rack while you are making observations.
- Place the
three remaining test tubes in a test tube rack. There should be only
three test tubes remaining.
- Add 2 mL of 3 M HCl solution to each test tube.
- Observe the relative rate of H
2 gas evolution for up to 5 minutes and record your observations on your report form.
- Based on the observations in the previous steps, list the elements that react in 3M HCl in order of increasing strength as reducing agents and write net ionic equations for all reactions.
Note: it would be helpful to draw a diagram to remember where the drops are on the sheet of metal before you begin.
Abdc
- Place a clean 1 inch-square of metal foil (sheet) of each of these metals Cu, Zn and Pb on a flat surface.
- Clean one side of the metal surface by sanding it with fine sandpaper or steel wool.
- Place one or two drops in spots of each of these solutions in a clockwise order on the metal surfaces:
| A. |
0.5 M Ag
+ |
| B. |
0.5 M Cu
2+ |
| C. |
0.5 M Zn
2+ |
| D. |
0.5 M Pb
2+ |
NOTE: Do not test a metal with a solution of the same metal ion, such as Cu metal with Cu
2+
ion.
- Watch for color changes in each spot as evidence of reaction. If you are not sure whether the reaction has occurred, rinse the plate with water. A distinct spot of a different color on the surface is good evidence for the reaction.
- Write net ionic equations for each reaction. Arrange Ag, Cu, Pb and Zn in order of their increasing strength as reducing agents. If a metal
A reacts with a cation of another metal
B , metal
A is a stronger reducing agent, more reactive than metal
B .
- Rinse and dry each square of metal and return it to the correct beaker on the reagent shelf for other students to use.
Part 4: flame tests
This station will be located inside a fume hood
Chemicals/Materials:
- 0.5 M Solutions of dissolved chloride salts of: Li, Na, K, Rb, Cs, Ca, Ba, Cu, Pb, Fe(II), and Fe(III), Sr (nitrate salt)
- Wooden splints, one per each solution
- Bunsen burner/clicker
- 1M HCl
- For each solution, take the splint out of the beaker and pass is through the flame of the Bunsen burner, remembering that the hottest part of the flame is the blue section in the center. Do not leave the splint in the flame too long as it will eventually catch on fire.
- Replace the splint in the same beaker from which it came.
- On your report form, record the color of the flame of each metal.
