In Part I, you will use information provided on cards to organize these cards in a particular pattern. Then, in Part III, you will conduct a laboratory exploration of some chemical properties of a few elements and examine the regularities in these properties. The properties observed for the elements will be used to predict the properties of other elements.

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To use periodic properties as a tool for organizing and predicting properties of elements.

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Wear protective glasses and aprons in Part II of this investigation. Avoid skin contact with solids and solutions. Care must be taken to use the Bunsen burner correctly. Wash your hands before leaving the laboratory.

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Part I (Student Activity in groups of 3 or 4)

1. Obtain a packet of cards from your teacher or make a packet by cutting up the sheet given to you. Note the information given on each card.
2. Organize the cards in vertical and horizontal rows in as many patterns as you can. Keep notes on patterns you identify. If a card appears to be missing, leave a space for it.
3. When time runs out, or you agree that the task is complete, sketch the best card arrangement on a sheet of paper. (Data Check: Obtain your teacher's initials on your sketch.)

Prepare data charts to record observations for the teacher demonstration and for your own activity in Parts II and III.

Part II (Teacher Demonstration)

Your teacher will add a universal indicator to each of three beakers. One piece of a different metal, Li or Na will be added to each beaker. Record all observations, including a comparison of the relative speeds of these reactions. The formulas for the hydroxides of the elements formed are LiOH, NaOH, and KOH. (Note K was omitted because potassium is on a list of hazardous substances which should not be in a high school laboratory.)

Part III

(Caution: Use a safety shield and handle metals and the solutions formed with care.)

1. Place 1 mL of distilled water and 2 drops of universal indicator in each of six 13 x 100 mL test tubes. Label these tubes 1 to 6.
   1. (Caution: Handle calcium with forceps.) To Tubes 1, 2, and 3 add small pieces of calcium, magnesium, and aluminum (one metal to each tube). Record observations immediately and again after 3 min.
   2. (Caution: Be sure that no flammable materials are present.) Heat (gently, in a low flame) any tube in which a reaction has not occurred after 3 min. Note any reaction that occurs at this higher temperature. The formulas for possible hydroxides formed are Ca(OH)₂, Mg(OH)₂, and Al(OH)₃.
2. Use a drinking straw to blow into the solution in Tube 4. (Your breath contains CO₂, among other gases.) Record the color of the resulting solution. For our purposes, the formula for the product of the reaction of CO₂ with water may be written as CO(OH)₂.
3. (Caution: Avoid contact of skin with these solutions.) Add two drops of SO₂(OH)₂ to Tube 5 and two drops of PO(OH)₃ to Tube 6. Note the color of each solution.
4. Dispose of the mixtures in the test tubes as directed by your teacher.
5. Wash hands thoroughly before leaving the laboratory.

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1. Predict the properties for the missing cards in your sketch for Part I of this investigation.
2. Universal indicator turns the following colors depending on the nature of the solution (see table below procedure). Using this table, list the formulas of the acidic OH compounds and the formulas of the basic OH compounds which you examined.
3. Where, on the periodic table, are the elements found that form basic OH compounds? What kind of elements are these?
4. Where, on the periodic table, are the elements found that form acidic OH compounds? What kind of elements are these?
5. Assuming that the results of this investigation are found in other horizontal rows (periods) of the periodic table, describe the trend in the acid-base nature of OH compounds as one moves across a horizontal row in the table.
6. 1. What similarities did you observe in the reactivity toward water of the three elements in the first group (vertical row) of the table?
   2. What is the trend, from top to bottom, in the reactivity of these elements with water?
7. Compare the reactivities of sodium, magnesium, and aluminum with water. What is the trend in the ability of these first three elements in Period 3 to react with water?
8. Summarize the patterns you observed in this activity both down a group and across a period in the periodic table

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1. One definition of an acid is a substance that produces hydrogen ions in aqueous solution. To emphasize this property, formulas of acids are often written with the hydrogen atoms first. Using this convention, rewrite the formulas of each OH compound that tested acidic in solution.
2. Why does knowing that phosphoric acid is H₃PO₄ help you to write the formula for arsenic acid?
3. When barium is burned to form an oxide and this oxide is dissolved in water, the OH compound of barium forms. Will the solution be acidic or basic? What is the formula of this compound?
4. Carbonated beverages and soda water contain CO₂ and water. What would be the color of universal indicator in soda water?

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Teachers Guide

Preparing for the Laboratory Activity

• Major Chemical Concept
• Level
• Expected Student Background
• Time
• Safety
• Materials
• Advance Preparation

Conducting the Laboratory Activity

• Pre-Lab Discussion
• Teacher/Student interaction
• Anticipated Student Results
• Answers to Data Analysis
• Answers to Imply, Apply
• Post-Lab Discussion
• Possible Extensions

Assessing the Laboratory Learning

• Laboratory Practical
• Student Investigations
• Materials
• Advance Preparation
• Safety
• Suggested Procedure
• Anticipated Student Results
• Paper/Pencil Items
• Answers to Paper/Pencil Items
• Check List Items
• The Laboratory Report

Preparing for the Laboratory Activity

Major Chemical Concept

Periodic trends in the reactivity of some representative metals with water can be experimentally determined and can be related to the acid-base nature of hydroxides (oxides dissolved in water).

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General and advanced chemistry

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Students should be able to:

• Use a Bunsen burner
• Decant liquids
• Estimate volumes
• Use indicators to distinguish acids and bases

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Part I: 30 min

Part II: 40 min

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• Solutions from the teacher demonstration and from Part III, Steps 2 and 6 are corrosive and should be handled carefully.
• Review procedures to use if spills occur.
• Use safety shield during demonstration of alkali metals in water.
• Li, Na, and Ca can cause burns and should be handled with care.

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Non-Consumables (per lab team)

• 1 Bunsen burner
• 6 Test tubes, 13 x 100 mm
• 1 Test tube clamp
• 1 Test tube rack

Consumables (per lab team)

• 1 Drinking straw
• 1 Dropper bottle of 3 M H₂SO₄
• 1 Dropper bottle of 3 M H₃PO₄
• 1 Dropper bottle of universal indicator
• Small piece (about rice grain size) of Li, Na, Ca, Mg, and Al.
• (Li and Na are used only for the teacher demonstration.)
• (Note K was omitted because potassium is on a list of hazardous substances which should not be in a high school laboratory.)

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1. Make a copy of the set of cards below for each student group or make permanent sets from different colored index cards. Place consecutive numbers (except for missing cards) in the upper left-hand corner and a periodic property of elements (ionization energies or atomic radii) in the upper right hand corner. Make sure that the periodic property for each group matches the color of the cards. You might also add the same symbol to like-colored cards.
2. 3 M sulfuric acid: 16.6 mL conc. H₂SO₄ per 100 mL solution
3. 3 M phosphoric acid: 19 mL conc. H₃PO₄ per 100 mL solution

Cards

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Conducting the Laboratory Activity

Pre-Lab Discussion

Explain, with examples, how organization aids the study of large quantities of information. Then let students sort themselves into groups using an either/or property. Students might choose glasses/no glasses; male/female. Each group then sub-divides within itself according to another property. Height, weight, and shoe size are examples of such properties.

(Caution: Alkali metals and the solution they produce in water must be handled with care.) For the teacher demonstration, use forceps to add small (no larger than a rice grain) pieces of the metals (Li and Na) to 1 L beakers nearly filled with water and containing 4 or 5 drops of universal indicator. Give students the formulas for the hydroxides formed.

You might need to help students make a table or chart for recording data. Examples of these are given below.

• Part II and Part III, Step 2
• Metal used
• Relative speed of reaction
• Color of indicator
• Formula of OH compound
• Part III, Steps 3 and 4
• Formula of OH compound
• Color of indicator

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Move around the laboratory during Part I to make sure all students are working and that the cards are arranged in some pattern. Some questions which might be asked during Part III are: (1) How can you determine the relative rates of the reactions? (2) What evidence do you have that a reaction is occurring? (3) How could you test for the identity of the gas evolved?

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For Part I, cards should be placed in horizontal or vertical rows with consecutive numbers. All cards of the same color will be in the same vertical or horizontal row and numbers in the upper right hand corner will increase or decrease horizontally or vertically.

Example:

For Part II

Teacher demonstration: All three elements zip around surface of water. Gas is given off. Indicator turns blue. Potassium reacts fastest, lithium slowest. Flame shows above globule of potassium.

Part III

Step 2 Calcium reacts vigorously in cold water, bubbles form, and tube heats up. The solution turns dark blue. Magnesium does not show much reaction in cold water but does react in hot water with bubbles; the solution turns blue. Aluminum does not react in hot or cold water.

Step 3 Solution turns orange-yellow.

Step 4 Both solutions turn red, although the phosphoric acid, PO(OH)₃ is slightly orange.

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1. For sample cards, the missing cards are numbers 4 and 11. The Number 4 card is green with an upper right hand number of about 0.95 and the Number 11 card is pink with a number of about 1.00

2. Acidic	Basic
   CO(OH)2	LiOH
   SO(OH)2	NaOH
   PO(OH)3	KOH
   Ca(OH)2
   Mg(OH)2

3. Elements that form basic OH compounds are on the left side of the table. They are metals.
4. Elements that form acidic OH compounds are on the right side of the table. They are non metals.
5. Changes from basic OH compounds to acidic OH compounds.
6. 1. All produced strongly basic OH compounds, all gave off a gas. All reacted vigorously.
   2. As the atomic number increased, the reactivity increased.
7. Sodium reacted vigorously in cold water, magnesium reacted slowly in hot water and aluminum didn't seem to react at all, even in hot water. As the atomic number increased, the reactivity decreased.
8. Elements in vertical groups seem to react alike and those in horizontal rows give different reactions. The reactivity of metals with water increased from top to bottom in a vertical row and decreased from left to right in a horizontal row.

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1. H₂CO₃, H₂SO₄, H₃PO₄
2. Arsenic is in the same period as phosphorus.
3. Basic
4. Orange

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The discussion for Part I should follow as soon as this part of the activity is completed. Have groups show their card arrangement and explain how they arrived at these. Discuss variations and similarities in properties and reasons for leaving gaps in the arrangement. This progresses to discussion of Mendeleev's efforts and predictions as well as subsequent table revisions. Point out the division line between metals and nonmetals and briefly give the organization of the chart into groups (families) and periods.

Help students see the patterns in Part II by relating what they did in Part I. Remind them that one set of observations only "suggests" a pattern and does not definitely prove it . This kind of evidence plus many other pieces of evidence support the periodic law. Natural follow-up to this activity is to analyze graphs of some periodic properties. Note how the property changes within a period as well as within a group.

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1. Determine the trends in solubilities of the alkaline earth carbonates.
2. Determine the trends in solubilities of the silver halides.
3. Create a naming system that could be used to identify the 20 cards on the chart which you sketch in Part I.

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Assessing the Laboratory Learning

Laboratory Practical

Comprehension of Acid-base properties of oxides

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Caution: solutions are corrosive. Wear protective glasses and aprons during this investigation. You have been given four dropper bottles, each containing an oxide dissolved in water. You also have an indicator which is red in a very acidic solution, orange in a mildly acidic solution and yellow in a basic solution.

Write a procedure and use it to determine which dropper bottles contain metallic oxides and which contain nonmetallic oxides.

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Non-Consumables

• 1 Stirring rod, glass
• 6 Test tubes, 13 x 100 mm

Consumables

• Methyl orange indicator
• 0.1 M KOH (0.6 g KOH per 100 mL solution)
• 0.1 M NaOH (0.4 g NaOH per 100 mL solution)
• 0.1 M HNO₃ (0.6 mL concentrated HNO₃ per 100 mL of solution)
• 0.1 M H₂SO₄ (0.6 mL concentrated H₂SO₄ per 100 mL solution)

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These solutions should be placed in dropper bottles labeled with letters or numbers. Other acids and bases could be used to produce a greater variety. Depending on their level, students might need written directions for setting up this investigation.

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• Protective glasses and aprons must be worn.
• Solutions are corrosive and should be handled with care.

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Add about 1 mL (20 drops) of each solution to separate test tubes and add one drop of methyl orange indicator to each tube. Students might add one drop of each solution to 1 mL of water and add the methyl orange to this. The results should be good in either case.

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The following observations are typical:

Checklist for assessment of skills used in the investigation:

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1. Suppose the numbers shown below represent the radii of elements on a portion of the periodic table. Use these values to estimate the radius of Element X.

   	1.66
   1.75	X	1.56
   	1.89

2. Plot the following data and use the graph to estimate the value of the electronegativity for element number 6.

   Atomic No.	3	4	5	6	7	8	9
   Electronegativity	1.0	1.5	2.0	x	3.1	3.5	4.1

3. Which would you expect to react faster with water, barium or calcium? Give evidence from the experiment to support your answer.

   Use the grid and the periodic table to answer Questions 4 through 7.

   Br	B	Li
   Sr	Cs	N

4. Which metal would react fastest with water?
5. Which would form oxides that dissolve in water to give acid solutions?
6. Which would form oxides that dissolve in water to give basic solutions?
7. Which element in the second period would neither react in hot nor cold water?
8. Which of OH compound would be best described by a formula starting with H: I or Sr?

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1. Greater than 1.56 and 1.66. Minimum is 1.66. Smaller than both 1.75 and 1.89. Maximum is 1.75. Possible range is >1.66 and <1.75.
2. Approximately 2.5
3. Barium, based on trends observed in the activity. Potassium was most active in its family and calcium was more active than magnesium.
4. Cs; it is the furthest down and to the left on the periodic table.
5. Br and N, these are nonmetals.
6. Cs, Sr, and Li; these are metals.
7. B; it is in the same group as Al which did not react with water.
8. I, since it is a nonmetal.

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The laboratory report should include the data, analysis of the data, summary of results, and interpretation of results. Students should conclude that elements, when arranged according to some obvious property, will show periodic changes in other properties. The summary should also include a statement of the trends observed for the reactivity of metals and the acid-base nature metal and nonmetal oxides.

The check list below might be helpful for grading the report.

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