The periodic table is the most recognized symbol in chemistry across the world. It is a valuable tool that allows scientists not only to classify the elements but also to explain and predict their properties. Similarities and differences that repeat among the elements give rise to so-called periodic trends, both across rows and within columns of the periodic table. Recognizing periodic trends in the physical and chemical properties of the elements is key to understanding the full value of the periodic table. Pre-Lab Question 1: What are periodic trends and where can they be found occuring in the periodic table?
This experiment will identify periodic trends in the activity of certain metals. The reactions of magnesium, calcium and aluminum with water and acids will be compared in order to determine the trend in metal activity within a group (Mg vs. Ca) and across a period (Mg vs. Al) in the periodic table. Metals that are very reactive can form bases (example: Calcium Hydroxide, Ca(OH) 2 ) when in the presence of water, Equation 1, and when they are in the presence of an acid they can form hydrogen gas (H 2 ) bubbles, Equation 2. Ca(s) + H 2 O(l) Ca(OH) 2 (aq) + H 2 (g) Equation 1 Ca(s) + HCl(aq) CaCl 2 (aq) + H 2 (g) Equation 2 We will perform a chemical test (bases turn litmus paper from red to blue) and make close observations of the reactions to determine the presence of these products and then use the data as evidence of the periodic trend of activity across period and down a group. Pre-Lab Questions Continued: 2. What is the purpose of the lab? 3. What evidence can be found that shows that our experiment is a success?
Calcium and magnesium are very reactive, flammable solids and possible skin irritants. Use forceps to handle these metals. Hydrochloric acid is toxic by ingestion and inhalation and is corrosive to skin and eyes; avoid contact with body tissues. Wear chemical splash goggles. Always wash hands thoroughly before leaving the lab. Pre-lab Questions Continued: 3. What hazards are associated with the use of calcium, magnesium and hydrochloric acid? 4. What safety precautions must be followed to protect against these hazards?
24-well reaction plate 50ml beaker Aluminum foil Calcium turnings Hydrochloric acid, HCl, 0.5M, 3ml Magnesium ribbon Water (distilled or deionized)
1. Obtain 2 pieces of calcium turnings (in a 50ml beaker), 2 pieces of magnesium ribbon, and a piece of aluminum foil. 2. Place a 24-well reaction plate on top of a sheet of white paper. 3. Use a pipet to add 20 drops of water to wells A1 A3. 4. Test the water in wells A1 A3 with a piece of red or neutral litmus paper and record the initial color of the litmus paper for this litmus test in the Data Table. 5. Using forceps add one piece of calcium to well A1. 6. Using forceps add one piece of magnesium ribbon to well A2. 7. Tear off half of the aluminum foil and roll into a loose ball. Add the aluminum metal to well A3. 8. Observe each well and record all immediate observations in the Data Table. If no changes are observed in a particular well, write NR (No Reaction) in the Data Table. 9. Test the water in wells A1-A3 with a piece of red or neutral litmus paper and record the changes for this litmus test in the Data Table. 10. Continue to watch each well for 1-2 minutes. Record any observations comparing the speed of the reactions. 11. Repeat steps 3 and 5-8 but instead of water add 20 drops of HCl to wells D1-D3. Record all observations on the Data Table. 12. Was there any evidence that a gas is being produced in wells D1-D3? Test by bringing a lit match to the space just above each well. Record any observations for this match test in the Data Table. A1 A2 A3 Ca, H 2 O Mg, H 2 O Al, H 2 O B1 B2 B3 A1 A2 A3 D1 D2 D3 Ca, HCl Mg, HCl Al, HCl
Calcium Magnesium Aluminum Reaction with H 2 O Observations Reaction with HCl Optional Litmus Test Observations Optional Match Test
1. Which group 2A metal, magnesium or calcium is more active? Cite your evidence. 2. Which period 3 metal, magnesium or aluminum, is more active? Cite your evidence. 3. Rank the three metals from most active to least active. 4. Write a Conclusion Statement that describes the periodic trend in metal activity down a group and across a period. Be sure to cite Evidence (Data) to support your Claim and include Commentary on why your claim is important in our understanding of the periodic table.
Pre-Lab Questions Data Table Post-Lab Questions