.

2. Add 25 mL distilled water to 100-mL beaker and place in ice to serve as an ice water rinse. Reserve.

3. To 20 g sodium chloride (NaCl) in a 400-mL beaker in a hood add 5 mL portions of 15 M NH₃ with continuous stirring, until the NaCl has dissolved and a total of 65-70 mL of aqueous ammonia has been added.

4. The addition of carbon dioxide may be carried out by adding powdered dry ice or making a carbon dioxide gas generator using marble chips and 6 M HCl.

Dry Ice Method

5. Add 65-70 mL powdered dry ice to the NaCl-NH₃ mixture with continuous stirring until precipitation occurs. Warm the reaction vessel to 10-15 °C occasionally by immersing the bottom of the beaker in the warm water bath. Add an additional 20-25 mL of dry ice continuing to stir until the bubbling of carbon dioxide ceases. Proceed to Step 6.

Carbon Dioxide Generator Method

5. The apparatus is set up as shown. Use glycerol to lubricate the glass tubing and thistle tube before inserting into rubber stoppers. Always use a towel wrapped around the tubing to protect your hands. Place 60 g marble chips into the gas generating bottle. Place 25-35 mL of water into the bottle clamped to the ring stand so that the end of the glass tubing is below the water level. Add 6 M HCl and bubble the carbon dioxide into a 250-mL or 500-mL Erlenmeyer flask containing your reaction mixture. Swirl the flask to assist the mixing operation until a large quantity of solid forms. This method takes quite a bit of time (about 1.5 h). Complete the synthesis as indicated in Step 6.

6. Cool the mixture in the ice bath. Suction filter the precipitate with a Buchner funnel fitted with filter paper and attached to a suction flask. With the suction off, pour 5 mL ice water over the precipitate, letting it soak into the precipitate. Reapply suction to remove the water rinse. Repeat the rinsing process with another portion of ice water. Repeat with 5 mL acetone. Pull air through the precipitate 5-10 min to initiate drying of the product. If desired, the product can be dried completely by transferring to an evaporating dish and drying at 110 °C for about two hours. (This is not necessary if you simply want to show the class the precipitate of NaHCO₃ . If a quantitative determination of yield is to be made, it is helpful to know that dry ice has a density of about 1.5g/mL).

Testing the Product

7. Dissolve a pea-sized portion of the product in 5-10 mL distilled water. Determine the pH with hydrion paper, universal indicator or pH meter.

8. Place a portion of the solid in a test-tube and add 2-3 mL 6 M HCl. Test the evolving gas with an eyedropper containing a hanging drop of saturated calcium hydroxide solution. (The drop becomes cloudy due to a white precipitate of CaCO₃.)

Discussion

The equation for preparation of NaHCO₃ (s) is:

The solid sodium hydrogen carbonate formed is separated by decantation or filtration. In the Solvay Process, the compound is then dried and heated to 175 °C to produce Na₂ CO₃.

Reactions for Testing the Product are:

Demonstration 4: Qualitative Analysis of Alkali Metal Ions

Materials 6

• 6 M Acetic acid, CH₃COOH, 10 mL [3.5 mL glacial (17 M) acetic acid diluted to 10 mL]
• 95% Ethanol, 20 mL (95 mL ethanol per 100 mL solution)
• 0.25 M Potassium nitrate, KNO₃ (2.5 g KNO₃ per 100 mL solution)
• 0.06 M Silver nitrate, AgNO₃ (1.7 g AgNO₃ in 100 mL solution)
• Sodium bitartrate, NaHC₄H₄O₆ , saturated solution, 2 mL (Add solid NaHC₄H₄O₆ to 2 mL H₂O with stirring and until no more dissolves.)
• Sodium cobaltinitrite, Na₃Co(NO₂)₆, solution (Prepare in hood. Dissolve 0.75 g Co(NO₃ )₂. 6H₂O in 3.0 mL of water; dissolve 6.0 g sodium nitrite (NaNO₂) in 3.0 mL of water; mix the two solutions with vigorous stirring. Add 1.5 mL glacial acetic acid. Dilute to 25 mL, let stand, filter.)
• 0.1 M Sodium nitrate, NaNO₃ (3.2 g NaNO₃ per 100 mL solution)
• Sodium per
• chlorate, NaClO₄, saturated solution, 2 mL (Add solid NaClO₄ to 2 mL H₂O with stirring and until no more dissolves.) Zinc uranyl acetate, Zn(UO 2 ) 3 (C 2 H 3 O 2 ) 8 , solution (Dissolve 5 g uranyl acetate, UO₂(C₂H₃ O₂)₂·2H₂O, in 1 mL glacial acetic acid diluting to 25 mL with water. In a separate container stir 15 g zinc acetate with 1 mL of glacial acetic acid diluting to 25 mL with water. Mix the two solutions, add 0.5 g sodium chloride, let stand overnight, and filter.)
• Ice bath

Safety

Sodium perchlorate is a highly reactive oxidizing agent. It is stable in aqueous solution and is traditionally used as a precipitant for K⁺ in qualitative analysis. Chlorates (MClO₃ ) and perchlorates (MClO₄ ) in solid form should be kept away from organic and other combustible solids and should never be handled with metal spatulas.

Directions

• Test for Potassium Ion

1. Place 3 mL KNO₃(aq) in each of three test-tubes. To the first test-tube add the following: 3 mL 95% (by volume) ethanol; 1 mL 6 M acetic acid; 1 mL AgNO₃ solution; and 3 mL Na₃Co(NO₂)₆. Stir and cool in an ice bath. A yellow precipitate of K₂ AgCo(NO₂)₆ indicates the presence of potassium ion. (The reaction would also precipitate NH₄⁺, Li⁺, andTl⁺ .)
2. To the second test-tube add 3 mL 95% ethanol and 2 mL saturated NaHC₄H₄O₆ . Stir and cool in an ice bath. A white precipitate of KHC₄H₄O₆ should form.
3. To the third test-tube add 3 mL 95% ethanol and 2 mL saturated NaClO₄. Do not heat! A white precipitate of KClO₄ will form upon cooling.

Test for Sodium Ion

Place 2 mL NaNO₃ (aq) in a test-tube. Add 6 mL zinc uranyl acetate, Zn(UO₂)₃(C₂H₃O₂ )₈(aq). Stir vigorously and cool in an ice bath. A greenish-yellow precipitate of NaZn(UO₂)₃(C 2 H₃O₂)₉. 5H₂O should form.

Demonstration 5: Reaction of Sodium with Water Reducing the Rate of Reaction

Purpose

To use an alternate method to demonstrate the reactivity of sodium with water. This demonstration gives students more time to observe the reaction.

Materials

Safety

With sodium and all alkali metals, always make sure you have a clean piece of the metal. Oxide coating on the metal surface may result in violent expulsion of the lump from the reacting vessel, with accompanying splashing out of the caustic hydroxide solution. Since kerosene is flammable, do not test for hydrogen gas with a lighted splint or other source of flame!

Procedure

1. Add a 3-5 cm layer water and 1-2 drops phenolphthalein to beaker.
2. Add a 3-5 cm layer kerosene to the vessel.
3. Carefully drop in a small piece of sodium.

Discussion

Since the relative densities are water > sodium > kerosene, the sodium will float at the interface between the two immiscible liquids. Reaction of the sodium with water will produce hydrogen gas, which will lift the sodium up into the kerosene layer where the reaction will cease. As the hydrogen gas is evolved the sodium will fall again to the interface and the entire cycle will be repeated. The cycles of reaction can thus be extended to several minutes. This approach increases the observing time for students, and also reduces the intensity of the reaction between the sodium and water.

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