Materials Included In Kit

Additional Materials Required

Safety Precautions

This activity requires the use of hazardous components and/or has the potential for hazardous reactions. Hydrochloric acid is corrosive to skin and eyes; avoid all contact with body tissue. Ammonium hydroxide is toxic by ingestion and inhalation of the vapor. It is very irritating to the eyes and respiratory tract; use a fume hood to prepare and dispense solution. Nitrates are strong oxidants and are a potential fire risk when in contact with organic material. Potassium chromate is highly toxic and is corrosive to skin, eyes and respiratory tract. Strontium and barium compounds are toxic by ingestion. Oxalates are toxic by inhalation and ingestion and are irritating to body tissue. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Provide good ventilation when using and dispensing these materials. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Neutralize the acid solution according to Flinn suggested disposal method #24b. Barium compounds should be disposed of according to Flinn Suggested Disposal Method #27h. Chromates should be disposed of according to Flinn Suggested Disposal Method #12a. All other solutions can be flushed down the drain with excess water.

Teacher Tips

• For Activity 3, there are more than enough materials for a class of 24 students (12 groups of 2). The kit contains 12 Flinn Scientific periodic tables, 180 cm magnesium ribbon, 25 g calcium and 500 mL of 1 M hydrochloric acid. However, since this lab is qualitative and amount is not crucial, you may stretch the materials to suit larger classes by using slightly less material. For example, for a class of 30 students (15 groups of 2), use 10 cm magnesium ribbon per group, 1 gram of calcium turnings per group, and 30 mL of HCl per beaker.
• Remind students not to inhale vapors by directly placing their nose over the beaker. Odors should be detected by wafting, waving the vapors toward the nose with a hand.
• You may extend the idea of periodic properties by demonstrating the greater reactivity of Group I metals versus Group II metals and also relating this to ionization energies. To do this, you can show the students the reactivity of both sodium and magnesium with water. (Caution: Observe all safety precautions when adding group I alkali metals to water. Refer to Flinn demonstration kit Safe Swimming with Sodium (AP8916) or to your current Flinn Scientific Catalog/Reference Manual for safety precautions regarding sodium).
• For Activity 4, there are more than enough materials for a class of 24 students (12 groups of 2). The kit contains 12 Flinn Scientific periodic tables, 120 disposable pipets (9 per group x 12 groups = 108), and 100 mL of each solution (4–5 mL per group x 12 groups = 48–60 mL). The extra may be used to repeat a test.
• Each group will need approximately 4–5 mL of each of the solutions (25–30 drops = ≈ 1 mL per well). You should have your students label their 9 pipets and fill them from the stock bottle. The pipets can be transported and stored bulb-down in a beaker. Labeling can be done with permanent marker or by taping a small piece of paper on the bulb.

Further Extensions

Activity 4. Analyzing the Solubility of Group II Metals

This lab may be extended to include practice in writing and balancing equations, net ionic equations, and solubility rules.

5. On a separate sheet of paper:
   1. Write a balanced equation for each reaction that occurred.

      Full equations followed by net ionic equations.

   2. Write a net ionic equation for each reaction. (Use a solubility chart to determine the formula of the solid precipitate.)

      Examples:

      {12794_Extension_Equation_1}
   3. Would sodium carbonate give the same or different reactivity as ammonium carbonate in this activity? (See the example equation provided.) Explain.

      Sodium carbonate, if used instead of ammonium carbonate, would give the same reactivity. Both compounds are water soluble, thus their ions are free in solution. Therefore the carbonate anion is free to react.

Sample Data

Activity 3. Comparing the Reactivity of Two Alkaline Earth Metals

Possible observations are provided in the following table. Encourage students to be as clear and descriptive as possible when recording observations.

Answers to Questions

Activity 1. Fill in the Missing Information

1. Which Group II metal did you find to be more reactive, Mg or Ca?

   Calcium is more reactive.

2. Study the position of the two elements on your periodic table. Write a general statement about period and reactivity.

   Ca is below Mg in the periodic table. As the period increases, reactivity increases for Group II metals.

3. Based on your observations in this activity, use the periodic table to predict which Group II element would be the most reactive, Be, Sr or Ba?

   Ba would be predicted to be the most reactive.

4. In this lab, you observed the ionization (or dissolving) reaction of two different metals in acid. When ionization occurs, the solid metal loses electrons to form the aqueous metal cation. For example:

   Mg(s) → Mg²⁺(aq) + 2e^– and Ca(s) → Ca²⁺(aq) + 2e^–

   The energy needed to cause this ionization to occur is called the ionization energy of the compound. The higher the ionization energy, the harder it is to lose electrons. Based on this information, which metal do you predict would have a higher ionization energy? Explain why.
   Magnesium would be predicted to have a higher ionization energy because it is less reactive and more energy is needed to ionize Mg to Mg²⁺.

5. How would tearing the magnesium ribbon into smaller pieces affect the reaction rate? Why?

   Smaller pieces would increase reaction rate due to an increased surface area.

6. List at least two other factors (besides particle size) that may affect the rate of the reaction?

   Possible answers are temperature, stirring, catalyst, surface area.

7. Write the balanced chemical equation for the reaction of magnesium with hydrochloric acid.

   Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

8. Write the balanced chemical equation for the reaction of calcium with hydrochloric acid.

   Ca(s) + 2HCl(aq) → CaCl₂(aq) + H₂(g)

1. A color change or the formation of a precipitate is an indication that a reaction has occurred. Which Group II metal (Mg, Ca, Sr or Ba) showed a reaction with the most compounds?

   Barium

2. Which Group II metal was the least reactive?

   Magnesium

3. List the four Group II metals in increasing order from least reactive to most reactive.
   {12794_Answers_Figure_4}
4. Compare this order to the position on the periodic table and write a general statement regarding reactivity and position in a group.

   Reactivity increases down a group.

Discussion

Activity 3. Comparing the Reactivity of Two Alkaline Earth Metals

The chemical activity of metals generally increases down the columns (group) in the periodic table. For example, compare the reactivity of lithium, sodium, and potassium. If placed in water, the three will react differently. Lithium will barely sizzle on the surface of the water, sodium will sizzle violently and possibly ignite and potassium will most likely react explosively when in contact with water. Group II (alkaline earth) metals react in a similar way; as you move down the family, the reactivity increases. Calcium proves to be much more reactive than magnesium with hydrochloric acid. The reactivity of all of these metals is related to their ionization energies. The lower the ionization energy the more vigorous the reaction. The first ionization energy for magnesium is 738 kJ/mol, whereas it is only 590 kJ/mol for calcium. Metals are generally organized in their groups by decreasing ionization energies (and increasing reactivity). The pattern becomes less pronounced as you move from Group I toward Group XII where the opposite pattern begins to be observed.

References

Becker, R. Twenty Demonstrations Guaranteed to Knock Your Socks Off!—Volume II; Flinn Scientific: Batavia, IL, 1997; pp 97–100.

Introduction

The Periodic Table of Elements is one of the most recognized, celebrated and useful aspects of chemistry. The Periodic Table organizes more than 100 elements and helps scientists summarize and visualize many known facts of chemistry. It also is the tool that displays, at-a-glance, the similarities and the differences among the elements. Complete four activities to become familiar with the elements and the periodic table.

Concepts

• Periodicity
• Reactivity
• Rates of reaction
• Solubility

Background

In 1869, the Russian chemist Dmitri Mendeleev (1834–1907) organized the known elements into a table. With a few exceptions, atomic weights increased regularly from left to right across the horizontal rows called periods. He found that certain elements repeated similar physical and chemical properties at specific intervals, and he organized these into vertical columns called groups or families (see Figure 1).

Experiment Overview

• Activity 1. Fill in the Missing Information—An introductory activity to familiarize students with the periodic table. The table has three categories: Symbol, Name and Atomic Number. Students are given one of the values and are required to find the other two by looking at a Periodic Table.
• Activity 2. The Ultimate Element Crossword Puzzle—This is an activity that will increase students’ knowledge of the elements and their common uses.
• Activity 3. Lab Activity: Comparing the Reactivity of Two Alkaline Earth Metals—Investigate the reactivity of magnesium and calcium with hydrochloric acid. 
• Activity 4. Lab Activity: Analyzing the Solubility of Group II Metals—Investigate the trends in solubility of alkaline earth metal cations.

Materials

Safety Precautions

Hydrochloric acid is toxic by ingestion or inhalation and corrosive to skin and eyes; avoid all contact with body tissues. Ammonium hydroxide is moderately toxic by ingestion and inhalation. Both liquid and vapor are extremely irritating, especially to eyes. It is very irritating to the eyes and respiratory tract. Potassium chromate is highly toxic and is corrosive to skin, eyes and respiratory tract. Strontium and barium compounds are toxic by ingestion. Oxalates are toxic by inhalation and ingestion and are irritating to body tissues. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Activity 1. Fill in the Missing Information

1. Use the Periodic Table provided to fill in the missing information.

1. Use the Down and Across clues provided to fill in the Ultimate Element Crossword Puzzle.

1. Obtain two 50-mL beakers and label them 1 and 2.
2. Using a graduated cylinder to measure, add 20 mL of 1 M hydrochloric acid to beaker 1 and to beaker 2.
3. Place a 12-cm piece of magnesium ribbon into beaker 1 and, at the same time, place 1–2 g of calcium turnings into beaker 2.
4. Cover each beaker with a watch glass and observe carefully.
5. Record your observations in the data table.
6. Continue to watch the reactions for three minutes.
7. Remove the watch glasses and record the temperature of each solution in the data table.
8. Record all observations in the table. Be sure to compare the rates of reactions in the two beakers.
9. Consult your instructor for appropriate disposal procedures.

1. Place a 24-well plate on the lab bench on top of a black sheet of paper.
2. Using a Beral-type pipet, place 30 drops (≈1 mL) of magnesium nitrate solution into each of five wells in a vertical column (e.g., Column A in Figure 1). Using a clean pipet for each solution, repeat with calcium, strontium and barium nitrate in subsequent vertical columns (see the reaction plate on the student worksheet.
3. Using a clean pipet, now add 30 drops of ammonium oxalate to the 4 wells containing magnesium, calcium, strontium and barium nitrate in the first horizontal row (e.g., Row 1). Observe the reactions in each well. Record your observations in the circles on the worksheet.
4. Using a clean pipet, add 30 drops of potassium chromate to the 4 wells in the second horizontal row. Observe the reactions and record observations in the table.
5. Using a clean pipet, add 30 drops of ammonium sulfate to the 4 wells in the third horizontal row. Observe the reactions and record observations in the table.
6. Using a clean pipet, add 30 drops of ammonium hydroxide to the 4 wells in the fourth horizontal row. Observe the reactions and record observations in the table.
7. Using a clean pipet, add 30 drops of ammonium carbonate to the 4 wells in the fifth horizontal row. Observe the reactions and record observations in the table.
8. Consult your instructor for proper disposal information.

Student Worksheet PDF

12794_Student1.pdf