Microscale Gas Chemistry:

General Safety Precautions.
    Always wear safety glasses.  Gases in syringes may be under pressure and could spray liquid chemicals.  Follow the instructions and only use the quantities suggested.

Toxicity.
    Ammonia has a pungent irritating odor and is a poisonous gas.  Exercise caution when working with poisonous gases and vacate areas that are contaminated with unintentional discharges of gas.
 

Suitability.
    Most of these experiments are suited for use as either classroom demonstrations or as laboratory experiments conducted by students.  Experiment 8 requires a fume hood and some finesse to get it work right.  Experiment 6 is a good classroom activity.  Experiment 9 is a good classroom activity because it uses several syringefuls of ammonia.
 

Syringe Lubrication.
    We recommend lubricating the black rubber diaphragm of the plunger with silicone spray (available from hardware stores) or medium-grade silicone oil (Educational Innovations, $5.95 Part #GAS-150; Fisher Catalog Number S159-500; $34/500 mL.)

Equipment. (This equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), Micro Mole, and Fisher Scientific.  Part numbers and links to their websites are provided.)

• 60-mL plastic syringes with a LuerLOK fitting
• Latex LuerLOK syringe cap fittings
• Plastic vial caps that fit within the barrel of the syringe
• Small plastic weighing boat
• Clear plastic beverage cup, 9 oz (260 mL)

3  mL concentrated ammonium hydroxide solution

     The NH3 gas samples used in these experiments are generated by heating concentrated ammonium hydroxide solution as follows.  Draw 3 mL strong ammonia solution into a clean dry 60 mL syringe.  Fit the latex syringe cap over the LuerLOK fitting.  Place syringe in 400 mL beaker of hot (60 - 70 ^oC) water for several minutes.  Care must be taken to stop the gas generation after the syringe is full.  This is done by removing the latex syringe cap while it is directed upwards.  Rotate the syringe 180^o in order to discharge the reaction mixture and then recap the syringe.  CAUTION! The liquid will vigorously spray out of the syringe.  In order to control the spray and minimize the ammonia odor, discharge the liquid at close range above the surface of a large (> 1 L) dish or basin of water.

     Several syringes of NH3(g) can be generated at the same time if a larger beaker (1-L) of hot water is used, however it is best to stagger their starting times in the hot bath so that they are not all ready to come out at the same time.  After the liquid has been discharged, store the NH3-filled syringes in the hot water bath until needed.
 

Preparation of Ammonia in the Microwave Oven.
     Samples of NH3(g) also can be prepared conveniently in a microwave oven.  (See details. )
 

Washing the gases.
    Do NOT wash the NH3-filled syringes.  Ammonia is extremely soluble in water.  Instead, it is possible to transfer the NH3(g) sample to a clean, dry syringe via a short length of latex tubing — although for the experiments described in this chapter, this is also unnecessary.

Disposal.
    Unwanted NH3(g) can be destroyed by bubbling the ammonia through water.
 
 

Experiment 1. Ammonia is Extremely Soluble in Water. Equipment: 250 mL beaker or plastic cup 15-cm length of latex tubing dish-washing basin, plastic Chemicals: NH3(g), 60-mL (one syringe for each experiment) 5 mL Universal Indicator 5 drops 1 M HCl(aq).      In a 250 mL beaker or plastic cup, prepare a solution of 100 mL distilled water, 5 mL Universal Indicator solution and 5 drops 1 M HCl(aq).    Experiment 1. Ammonia Fountain.      Remove the syringe cap from an ammonia-filled syringe and suction 2-3 mL of the solution into the syringe.  Keep the syringe’s LuerLOK fitting under the surface of the water and firmly hold the plunger in place so that it is not pulled into the syringe body.  (There is a considerable force pulling the plunger inward!)  Because NH3(g) is so soluble with water, additional water is rapidly suctioned into the syringe creating a small "fountain."

Experiment 1A. The Ammonia Fountain

Experiment 2. Plunging In!
    Remove the syringe cap from an ammonia-filled syringe and replace it with a 15-cm length of latex tubing.  Hold the syringe by the barrel and not by the plunger for this next part!  Suction 2-3 mL of the solution into the syringe and then pinch the tubing closed with your fingers.  The plunger will rapidly be pulled inward as the ammonia dissolves in the water.  (The action is so fast that it may be surprising to some.)
 

Experiment 3. Out of Control!
    Fill a plastic 3 gallon container such as a basin for washing dishes with water.  Remove the latex cap from an NH3-filled syringe and toss it LuerLOK fitting first into the container of water.  The syringe plunger will be pulled spontaneously inward with a considerable force that causes the water to be splashed about.
 

Experiment 4. Ammonia's Water Solubility is Temperature-Dependent.
Equipment:

• 800-mL beaker or cut off 2-L plastic beverage bottle

• NH3(g), 60-mL
• ice

Experiment 5. Ammonia is a Base.
Equipment:

• 1 or 2-L plastic beverage bottle
• 15-cm length of latex tubing

• NH3(g), 60-mL
• 20 mL Universal Indicator solution
• 25 drops 1 M HCl(aq)

Experiment 6. Acid-Base Reactions with Fruit Juices.
Equipment:

• 12-well plate

• NH3(g), 60-mL
• Variety of fruit drinks (students bring samples)

Experiment 7. Gaseous Ammonia Reacts with Gaseous Hydrogen Chloride.
 

Equipment: 15-cm length of latex tubing one additional clean, dry syringe plastic cup, 9-ounce or 250-mL Chemicals: NH3(g), 60-mL Concentrated HCl(aq), a few drops

Figure 1

Experiment 7A.
    Equip a syringe with a 15-cm length of latex tubing.  Fill the syringe with gaseous hydrogen chloride by suctioning the headspace fumes of HCl(g) from a bottle of concentrated hydrochloric acid.  (The contents of this syringe will be mostly air with varying amounts of gaseous HCl.)  Connect the HCl(g)-filled syringe with an NH3-filled syringe as shown in Figure 1.  Slowly push on the plunger of the ammonia syringe to produce plumes of white NH4Cl(s) in the HCl-filled syringe.  Variant:  Tap firmly on the plunger of the NH3-filled syringe so that the plunger moves inward 1 - 2 mL at a time.  This will produce interesting "smoke rings" in the HCl-filled syringe.

Experiment 7B.
    Place 3 - 5 drops of concentrated HCl on the bottom of a beaker or plastic cup.  Cover the container with plastic coffee can cover or equivalent.  After a few minutes, slowly dispense NH3(g) into the vicinity of the drops.  White clouds of NH4Cl(s) will form and the drops of HCl will become covered with white, solid NH4Cl.
 

Experiment 8. Ammonia Forms Nitric Oxide in the Ostwald Process.
Equipment:

• Fume hood
• 30 cm length of 20 gauge copper
• glass stir rod or pencil
• 3-cm length of latex tubing
• Bunsen burner
• pliers or tongs

• NH3(g), 30-mL
• O2(g), 60-mL (See: Preparation of Oxygen)

    The nitric oxide is converted to NO2(g) and then to nitric acid.  In the actual Ostwald process, screens made from platinum are used as the catalyst.

  Transfer 30-mL O2(g) from the O2-filled syringe to the NH3-filled syringe with the aid of a 3-cm length of latex connecting tubing.   The gases do not react so that it is necessary to maintain the same total volume by pulling the NH3 plunger outward as the O2 plunger is pushed inward.  Remove the latex tubing from the syringe filled with a mixture of NH3 and O2 and cap the opening with a latex syringe cap.

This reaction should be done in a working fume hood. In this experiment we will use a coil of copper wire.  Construct a coiled copper wire as shown in Figure 2 by winding a 30 cm length of 20 gauge copper around a glass stir rod or pencil.  The coils should be close to one another.  Prepare a syringe filled with O2(g).  Light a Bunsen burner and adjust the flame so that it is hot.  Set the coiled wire and a pliers or tongs near the burner for use later.

Figure 2

     Remove the latex syringe cap from the gas mixture.  While holding the copper wire with the pliers or tongs, heat the coiled portion of the wire at the top of the flame's inner cone until it glows brightly red.  Remove the coil from the flame and quickly start to discharge the gas mixture at ‘point blank’ range to the red hot copper (but not touching it).  The coils will glow as the wire catalyzes the reaction.  The heat given off from the reaction maintains the copper at red heat. More than one attempt may be necessary before this works properly.  As the reaction proceeds, note the reddish colored NO2 gas generated by the reaction of NO(g) with the O2(g) present.  Caution:  The syringes are easily damaged by heat so avoid contact between the hot coil and the syringe barrel.
 

Experiment 9. Ammonia Forms Complex Ions with Transition Metals.
Equipment:

• 12-or 24-well plate

• NH3(g), 60-mL (one syringeful per solution)
• CoCl2(aq), 3 ? 5 mL, faintly pink
• CuSO4(aq), 3 ? 5 mL, faintly blue
• NiCl2(aq), 3 ? 5 mL, faintly green
• AgNO3(aq), 3 ? 5 mL, dilute

One syringeful of NH3(g) may be necessary for each of these experiments.  Equip the syringe with a 15-cm length of latex tubing.  Into each well slowly discharge enough NH3(g) through the solution to achieve the desired results, namely a transparent solution of stated color.  If the precipitate has not disappeared by the time the volume of NH3(g) is reduced to 10 mL, hold the latex tubing in the metal ion solution until the solution moves up the latex tubing and into the syringe body.

    Dispose of metal ion solutions according to local regulations.
 

Left photo: Left column of cells: Top to Bottom: Co⁺², Cu⁺², Ni⁺², and Ag⁺.
Left photo: Right column: After addition of some gaseous ammonia.

Right photo: Left column of cells: same as Left photo, left column of cells.
Right photo: Right column: After addition of more gaseous ammonia.

(Middle column of cells are empty in both photos.)

  At the end of the experiments, wipe excess lubricant off of rubber diaphragm. Clean all syringe parts (including the diaphragm), caps and tubing with soap and water.  Use plenty of soap to remove oil from the rubber seal.  This extends the life of the plunger.  It may be necessary to use a 3-cm diameter brush to clean the inside of the barrel.  Rinse all parts with distilled water.  Be careful with the small parts because they can easily be lost down the drain. Important: Store plunger out of barrel.