Periodicity of Properties

Periodicity of Properties

Description

A wide range of chemical reactions is performed, and the acid/base properties of the products are studied.

Set

Oxides may be classified on the basis of a color change with litmus: red (acidic), or blue (basic). When oxides are not very soluble, they are classified on the basis of whether or not they dissolve in acidic or basic solutions. Basic oxides dissolve in acids; acidic oxides dissolve in bases. Oxides that dissolve in both acids and bases are called amphoteric oxides.

In this experiment you will test a number of oxides and classify them as acidic, basic, or amphoteric.

Hazards

Calcium oxide, barium oxide, 6 M HCl, and 6 M NaOH are corrosive.

Precautions

Use normal precautions (goggles and gloves) when handling CaO, BaO, 6 M HCl and 6 M NaOH.
Keep the CaO and BaO dry. (Store in "zipper" locking plastic bags.)
Eye protection is always a part of normal laboratory attire. Wearing goggles is essential for safety during this experiment.

Procedure

Set three test tubes in a rack. Add 5 mL of water to the first test tube, 5 mL of 6 M HCl to the second test tube, and 5 mL of 6 M NaOH to the third test tube. Add a small sample (not more than 0.1 g) of CaO in each of the test tubes. Stir each mixture. Note and record any evidence for dissolving. Use the symbol 0 for no dissolving, + for some dissolving, and * for very soluble.
Test the water solution with litmus.
Repeat this procedure for BaO and MgO.
Prepare carbon dioxide. Add 6 M HCl to about one gram of calcium carbonate (CaCO₃) contained in a gas-generator bottle or test tube. Immediately insert a stopper with a delivery tube. Bubble carbon dioxide through some distilled water in a large test tube.
Dry Ice, bottled CO₂, or your breath may be also used as a source of carbon dioxide.
Record solubility and acidity for each of the demonstrations done by the instructor also.
Use the records to classify each oxide as acidic or basic. Acids dissolve in base and turn blue litmus red. Bases dissolve in acid and turn red litmus blue.
On a blank piece of paper, sketch a periodic table giving element symbols and formulas of oxides. On this table, enter the classification for the oxide as acid or base. Make any appropriate generalizations.

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Instructor demonstration only- Use a plastic spoon or spatula to place a small sample (size of a split pea) of sodium peroxide (Na₂O₂) in the center of a watch glass. Add 1-2 mL of water to the sample; stir with a glass rod. Test with litmus paper. Record observations.
Instructor demonstration only- Work in a hood. Place 10 mL of distilled water in a wide mouth bottle. Place some sulfur in a clean deflagrating spoon. Insert the spoon handle through the hole in a 10- x 10-cm card. Ignite the sulfur in a burner flame.
- Once the sulfur is burning, transfer to the air space in the bottle, and cover with the card.
- Swirl the water to allow oxides being formed to dissolve. Test the resulting solution with litmus.
Instructor demonstration only- Work in a hood. Repeat using phosphorus. Handle the phosphorus with extreme caution. Place 10 mL of distilled water in a wide mouth bottle. Use a spatula to place a small sample of red phosphorus (two split peas) in a clean deflagrating spoon. Insert the spoon handle through the hole in a 10- x 10-cm card. Ignite the phosphorus by heating the spoon in a Bunsen flame. Once the phosphorus is burning, transfer to the air space in the bottle, and cover with the card. Swirl the water to allow oxides being formed to dissolve. Test the resulting solution with litmus. Record observations.
Instructor demonstration only- Work at the hood. Use caution. Place 10 mL of concentrated nitric acid in a test tube. Add a piece of copper metal and immediately insert a stopper provided with a delivery tube. A mixture of NO (nitric oxide) and NO₂ (nitrogen dioxide) is produced, which immediately oxidizes to brown nitrogen dioxide in air. This gas is toxic. Pass the emerging gas through a large test tube half-filled with distilled water.
- Test the solution with litmus paper.
- Record observations.

Handout

Name _____________________________ Class _______

Teacher______________________________

DoChem 032 Periodicity of Properties

Makeup student should watch the movie and record the data from the movie.

Nature of Metallic Oxides:

Formula	Litmus	Class	H₂O Sol.	6 M HCl Sol.	6 M NaOH Sol.

Nature of Nonmetallic Oxides:

Oxide	Litmus	Class

Teachers Guide

Purpose

To seek periodic relationships in the properties of elements through a study of their oxides.

Materials

sodium peroxide (Na₂O₂)
calcium oxide (CaO)
magnesium oxide (MgO)
barium oxide (BaO)
5 mL 6 M NaOH solution
5 mL 6 M HCl solution
litmus paper
4 25x200 mm test tube
stirring rod
watch glass
distilled water
pH paper
4 10-mL graduated cylinder
fume hood
red phosphorus
sulfur
calcium carbonate (or bottled CO₂ or Dry Ice)
copper metal (punchings; a pre-1982 penny works well)
concentrated HNO₃
litmus paper
4 25 x 200 mm test tube
2 deflagrating spoon
2 10 x 10 cm card, with hole
2 wide mouth bottle
1 gas delivery apparatus consisting of a 1-hole stopper to fit tube, glass nipple, 25-cm rubber tube, and second glass nipple for end of rubber tube
microspatula
Bunsen burner

Lab Hints

Omit the burning of the phosphorus and sulfur and the reaction of a penny if a hood is not available. Demonstrate these portions of the experiment; do not allow students to handle phosphorus.
Some familiarity with the concept of periodicity is needed for the student to obtain full benefit from the lab. The follow-up discussion is very important.

Time

Teacher preparation: one hour per day

Class Time: 40-50 minutes

Hazards

Phosphorus is extremely toxic and flammable. Concentrated nitric acid causes burns. The fumes of phosphorus oxide, sulfur oxide, barium oxide and nitrogen oxide are toxic. Sodium peroxide can react explosively with water. Calcium oxide, barium oxide, 6 M HCl, and 6 M NaOH are corrosive.

Precautions

The burning of phosphorus and sulfur and the generation of nitrogen (IV) oxide should be performed by the instructor under a hood. Only the instructor should handle sodium peroxide.
Wear gloves when handling phosphorus. Be certain that all of the phosphorus placed in the spoon is oxidized.
Be certain that all of the sodium peroxide sample removed has been reacted.
In case of contact with concentrated nitric acid, immediately flush eyes or skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Call a doctor.
Use normal precautions (goggles and gloves) when handling CaO, BaO, 6 M HCl and 6 M NaOH.
Keep the CaO and BaO dry. (Store in "zipper" locking plastic bags.)
Eye protection is always a part of normal laboratory attire. Wearing goggles is essential for safety during this experiment.

Disposal

Treat the barium solutions with an equal volume of 10% aqueous sodium sulfate. Wait one week. Filter. Save the barium sulfate for disposal with toxic solid wastes.
Heat the deflagrating spoons in a hot flame for 10-15 seconds to burn any remaining phosphorus or sulfur and thereby dispose of them.
Sodium peroxide may be destroyed by adding small amounts of the solid to large amounts of water with stirring. Neutralize the resulting solution with vinegar and dispose of at the sink.
The other chemicals may be disposed of with normal solid wastes or at the sink. Neutralize acids and bases before disposal.

Sample Data

Closure?

Closure Questions:

Predict the acid/base properties of SrO.
Predict the acid/base properties of Cl₂O and Cl₂O₅ and compare these predictions.

Answers to Closure Questions:

SrO is predicted to be basic, and similar to CaO.
Cl₂O and Cl₂O₅ are predicted to be acidic. Cl₂O₅ is predicted to be more acidic than Cl₂O. Describe how this can be confirmed by experiment.

Background

Sample Reactions:

Bases: CaO(s) + H₂O --> Ca(OH)₂(aq)
Acids: SO₂ + H₂O --> H₂SO₃

Metals form basic oxides. When several oxides are possible, the higher oxidation forms are more basic. Nonmetals form acidic oxides. When several oxides are possible, the higher oxidation forms are more acidic. Elements near the border between metals and nonmetals in the periodic chart form oxides that are amphoteric -- that is, they react as acids with bases, and as bases with acids. One way to study such an oxide is to make freshly prepared aluminum oxide by precipitation from 0.1 M AlCl₃ using 6 M NH₃. Wash the resulting material with very large amounts of water. Test the solubility of this gelatinous material in 6 M HCl and 6 M NaOH.

These observations support notions of the periodic variations in the properties of elements. (See Figure below.)

Key Words

acid
base
metal oxide
nonmetal oxide
oxidation
solubility
periodic properties

Conclusions

Metallic oxides react with water to form bases; their solutions turn red litmus blue.
Nonmetallic oxides react with water to form acids; their solutions turn blue litmus red.