Microscale Gas Chemistry:
Link to ammonia data page including physical properties.
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.
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.
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.
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)
The only chemical required for NH3 production is 3 mL concentrated ammonium hydroxide solution. This quantity will produce approximately 60 mL of NH3. The production of NH3 is relatively slow and it typically takes between 20 - 60 seconds to fill a syringe with NH3. The reaction is:
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 180o 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.
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
of Ammonia in the Microwave Oven.
Samples of NH3(g) also can be prepared conveniently in a microwave oven. (See details. )
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.
Unwanted NH3(g) can be destroyed by bubbling the ammonia through water.
1. Ammonia is Extremely Soluble in Water.
Experiment 1. Ammonia Fountain.
The Ammonia Fountain
Experiment 2. Plunging
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.
NH3(aq) NH3(g) DH = +34.2 kJ/mol DS = +81.3 J/mol K
Experiment 5. Ammonia is
Experiment 6. Acid-Base
Reactions with Fruit Juices.
Experiment 7. Gaseous Ammonia
Reacts with Gaseous Hydrogen Chloride.
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.
4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) DH = -907 kJ
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.||
Experiment 9. Ammonia Forms
Complex Ions with Transition Metals.
||Initially forms green-blue precipitate; then forms soluble orange [Co(NH3)6]Cl2(aq)|
||Initially forms pale blue-green precipitate; then forms soluble deep blue-purple [Cu(NH3)4]SO4(aq)|
||Forms soluble purple [Ni(NH3)6]Cl2(aq)|
||Initially forms brown precipitate; then forms soluble colorless [Ag(NH3)2]NO3(aq)|
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.
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.)
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
|This article first appeared in Chem13 News in March, 1997. It was written by Bruce Mattson, Department of Chemistry, Creighton University, Omaha, Nebraska 68178 USA|
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(This page last updated 29 January 2002)