http://www.woodrow.org/teachers/ci/faraday/lab4.html

The 1827 Christmas Lectures
of Michael Faraday

Demonstration of Lecture #4 Today

Nitric Acid or Aquafortis -- Ammonia or Volatile Alkali -- Muriatic Acid or Spirit of Salt -- Chlorine

Teacher Presentation

Today's interpretation is in two parts:

1.  Demonstration notes (e.g. lesson plans) of how Faraday might have planned for his lectures if he were to step into today's classroom;

2.  A more detailed description of the modern day interpretation for performing some of his actual experiments, or experiments which illustrate the same principles he showed. Included in this are the demonstrations performed by the group in the re-enactment of this lecture at the close of the WWNFF Institute, July 1992.

It should be noted that some of Faraday's methods and materials used are currently considered hazardous for safety or health reasons. Selected modern day demonstrations that are hazardous or difficult to perform are available on videodisc or tape.

For the corresponding original experiments, click on the icons .

Nitric Acid

Lab. 2: Acidic Properties Using Indicators

PURPOSE / To demonstrate the acidic properties of nitric acid using indicators.
MATERIALS / Test-tube rack, 3 test tubes, nitric acid solution, litmus paper, cabbage juice, turmeric solution, droppers for indicators.
HAZARDS / Nitric acid is very corrosive. It may cause burns to skin or damage clothing. Flush any exposed area with water immediately.
PROCEDURE / Pour a milliliter of dil. nitric acid into test tube. Test with litmus and watch for color change. Repeat with cabbage juice. Repeat with turmeric.
DISPOSAL / The acid may be poured down the drain and flushed with plenty of water.
DISCUSSION / Distilled water with a known acid or base may be used to compare color changes. Litmus turns red in an acid and blue in a base. Red cabbage juice is red in acid and green in base. Turmeric is pale yellow in acid, orange when neutral, and red-brown in a strong base.

Lab. 4: Nitric Acid Stains - (a Xanthoproteic Reaction)

PURPOSE / To show the effect of nitric acid and ammonia on natural materials.
MATERIALS / 25 mL 3M HNO3, 25 mL 3M NH3 small pieces of wool (washed), silk, cotton, etc.
HAZARDS / Nitric acid and ammonia should be handled with care; wear goggles and apron.
PROCEDURE / Dip each piece of fabric into warm dilute acid. The wool and silk will change to a yellow color; cotton shows no change. Then dip each fabric in the ammonia. The natural fibers of wool and silk change to a bright orange; cotton remains unchanged. You may continue to dip fabrics back and forth between solutions, noting the color changes.
DISPOSAL / Neutralize both solutions and flush down drain.
DISCUSSION / Nitric acid also produces a yellow stain on skin. In the ``Xanthoproteic Reaction'' from Practical Physiological Chemistry, by Hawk, Oser and Summerson (McGraw-Hill: New York, 1954) the authors reacted 2-3 mL egg albumin with 1 mL conc. HNO3, which was warmed and changed to yellow. It was allowed to cool and NH4OH was added to excess and the orange color appeared. The authors suggested that the reaction could also be done with 0.1% phenol solution instead of the protein. Explanation: ``Due to the presence of the phenyl group -C6H5 in protein molecules with which HNO3 forms certain nitro-modifications. The particular complexes of the protein molecules which are of special importance (e.g. egg albumin), are those of tyrosine and tryptophan.''

Lab. 5: Copper and Nitric Acid

PURPOSE / To show the different reactions between concentrated and dilute nitric acid and copper.
MATERIALS / Conc. HNO3, deionized water, 2 -50 mL grad. cylinders, 2 -150 mL beakers, 2 copper pennies (pre-1982) or pieces of copper.
HAZARDS / Handle nitric acid with caution (goggles and apron). Perform this demonstration in fume hood.
PROCEDURE / Add 25 mL of conc. acid to one beaker. To the second beaker, add 12.5 mL conc. acid + 12.5 mL water. Place a penny in each beaker. Note color differences/similarities of solutions and gases formed in each.
DISPOSAL / Allow each reaction to come to completion, then neutralize and flush down drain with plenty of water. Copper pieces may be discarded.
DISCUSSION / Reactions (redox) are as follows: (Conc. acid) Cu + 4 H+ + 2NO3- --> Cu2+ + 2 NO3- + 2 H2O (Dil. acid) 3 Cu + 8 H+ + 2 NO3- --> 3 Cu2+ + 2 NO + 4 H2O Different concentrations of nitric acid produce different gases: dark- brown NO2 mixed with colorless NO. Both produce the blue Cu2+ ion. Alternative: ``The Periodic Table'' (videodisc) Journal of Chemical Education Software: Sequence #29501-30261 shows the reaction with two concentrations of nitric and hydrochloric acids.

Ammonia

Lab. 13: Alkaline Properties of Ammonia

PURPOSE / To illustrate the alkaline properties of ammonia.
MATERIALS / Hotplate, test tube rack, 3 test tubes with rubber stoppers, NH3(aq), litmus solution, red cabbage juice, turmeric solution.
HAZARDS / Ammonia is irritating to the respiratory system and eyes, and can cause severe burns. Mixtures of ammonia gas and air can be explosive and should be kept away from sparks.
PROCEDURE / Gently heat a test tube containing an aqueous ammonia solution in a water bath on the hotplate. Waft the gas to detect the odor. Add litmus to the test tube and note color change. Repeat with a different test tube and cabbage liquor as the indicator. Repeat using turmeric as the indicator.
DISPOSAL / Fill ammonia, generating tube with water. Flush all solutions down drain.
DISCUSSION / The normal boiling point of ammonia is -33.35°C. It is a colorless gas with pungent odor and is extremely soluble in water. A saturated solution at 25°C is 34% by weight of ammonia. The solution is basic.

Lab. 14: Solubility of Ammonia in Water

PURPOSE / To demonstrate the solubility of ammonia in water.
MATERIALS / 250 mL round flask fitted with two hole stopper and long piece of glass tubing (see teaching diagram), 500 mL beaker, ring stand with clamp, phenolphthalein, eye dropper, concentrated NH4OH or bottle of compressed NH3 gas.
HAZARDS / Use same care in handling ammonia as in previous experiment.
PROCEDURE / Set up apparatus: insert glass tubing in rubber stopper. Fill eye-dropper with water and insert in other hole in stopper, insert in round flask. Fill beaker with water and add a few drops of phenolphthalein. Invert round flask and clamp as shown (teaching diagram). Flask must be dry. Add NH3 from compressed gas bottle (or generate and collect some as suggested in previous experiment). Squeeze a little water into the flask from the eye dropper. The fountain effect is observed as the NH3 dissolves in the water. Note change in indicator color. (Ammonia can also be generated by method in Lab. 22.)
DISPOSAL / Carefully dilute all solutions and flush down drain.
DISCUSSION / The extreme solubility of NH3 causes it to dissolve immediately in the small amount of water squirted into the flask. With a resulting decrease in pressure in the flask, the water will rise quickly giving the ``fountain'' effect. The color change in the indicator indicates the presence of the base. NH3(g) + H2O (l) --> NH4+ (aq) + OH- (aq) Also demonstrated on videodisc: ``Chemistry at Work'', Sequence: B-03752.

Lab. 17: Ammonia and Acid Neutralization

PURPOSE / To illustrate the ability of ammonia to neutralize an acid.
MATERIALS / Test tube rack, 6 test tubes with rubber stoppers, dil. NH4OH, dil. HNO3 in dropper bottle, litmus solution, red cabbage juice, turmeric solution, distilled water.
HAZARDS / See previous lab (Lab. 13)
PROCEDURE / Place a small quantity of each indicator in each of three test tubes. Add ammonia solution. Then add acid, drop by drop, until a color change is noted. Compare with water and indicator to find the neutral point.
DISPOSAL / Dilute solutions and flush down sink.
DISCUSSION / Ammonia is a base and can be neutralized by acid solutions. Litmus is blue in base, red in acid. Red cabbage juice will be green to greenish- yellow in base, blue when neutral, and red in acid. Turmeric will be reddish-brown in base, yellow-orange when neutral, and yellow in acid.

Lab. 22: Combustion of Ammonia

PURPOSE / To show that ammonia gas will burn in the presence of oxygen.
MATERIALS / Y-tube apparatus for mixing gases (as shown in illustrated notes for this lecture), ammonia generator (10 g NH4Cl and 10 g Ca(OH)2; add 10 mL distilled water and heat gently), oxygen generator (3% H2O2 and 3.0 g KMnO4 dissolved in 60 mL 3M H2SO4), candle.
HAZARDS / Generate small quantities of NH3 and O2. Be prepared to pinch shut the O2 line in case flame backs into apparatus. Dismantle oxygen generator immediately after use. Ammonia: same hazards as in above experiments.
PROCEDURE / Set up gas generators and connect to Y-tube. Add pea-sized sample of MnO2 ONLY to generator. Use pinch clamp to shut line to O2 generator. Begin generation of NH3. Fill inverted beaker with NH3. (A piece of red litmus placed at mouth will indicate that beaker is full.) Remove fill tube. Bring candle flame to mouth of beaker and watch for bright flash as NH3 ignites. Pour a small amount of H2O2 into oxygen generator and repeat using a mix of NH3 and O2. (Alternative: light mix of the two gases as they emerge from the Y-tube.)
DISPOSAL / Fill generator flasks with water and flush down sink.
DISCUSSION / This demonstration shows that NH3 is flammable in both air and pure oxygen. The reaction with oxygen is more dramatic. Both reactions are strongly exothermic: 4 NH3 + 3 O2 --> 2 N2 + 6 H2O

Hydrochloric Acid

Lab. 24, 26, 31: Preparation and Properties of Hydrochloric Acid

PURPOSE / To show the preparation of HCl and demonstrate its solubility and its effect on various indicators.
MATERIALS / 250 mL flask with ground glass opening, 500 mL flask with ground glass opening, ground glass joint, conc. H2SO4, NaCl solid, indicators (litmus, turmeric, universal), ground glass stopper, large beaker or transparent container, dilute NaOH.
HAZARDS / HCl should be prepared under a hood and care taken as vapors are corrosive and should not be inhaled.
PROCEDURE / Join 250 mL flask (gas generator) to 500 mL flask using a vented ground glass connection for collection of HCl by upward displacement of air. Under the hood disconnect 250 mL flask from apparatus and add 10 g of solid NaCl to the flask and about 20 mL conc. H2SO4. Immediately reconnect apparatus. Allow 500 mL flask to fill with ``fog'' of HCl; (excess HCl will be vented through side-arm of flask or of ground glass joint). Disconnect 500 mL flask from apparatus, stopper, and slowly add dil. NaOH to 250 mL flask to stop reaction. Demonstrate solubility of HCl in water with same procedure as with NH3 (Lab. 14). Test the solution of HCl formed above with litmus, cabbage juice and turmeric. Universal indicator could have been added to the water in the solubility demonstration to show formation of the acid.
DISPOSAL / Carefully dilute all solutions and flush down drain.
DISCUSSION / Formation of HCl (at moderate temperatures): NaCl + H2SO4(r) NaHSO4 + HCl (at higher temperatures): NaCl + NaHSO4 --> Na2SO4 + HCl (combining both steps): 2 NaCl + H2SO4 --> Na2SO4 + 2 HCl

Lab. 34: Reaction of Hydrochloric Acid and Ammonia (also illustrates Graham's Law of Diffusion)

PURPOSE / To illustrate the reaction of NH3 and HCl and [qualitatively/semi-quantitively] show the progressive rate of diffusion of these gases, using pH paper.
MATERIALS / Glass tube (length may vary up to 75 cm, inside diameter up to 3 cm - smaller tubes work faster), ring stand with clamp to hold glass tube, conc. HCl, conc. NH3, 2 corks to fit ends of tube, Q-tips or cotton balls attached to corks, pHydrion paper a little longer than length of tube.
HAZARDS / Conc. acids and bases should be handled with care (goggles and gloves). Product formed (NH4Cl) is irritating - use in well-ventilated room.
PROCEDURE / Pull a piece of full-range pH paper through the entire length of the glass tube, tape ends to outside of tube (attach heavy paper clip to one end of paper and let it fall through). Attach tube to clamp so that it is horizontal. Attach Q-tips or cotton balls to corks, soaking one in HCl, the other in NH3. Place corks simultaneously in opposite ends of tube. Note rate of diffusion by color change in pH paper. Note distance of the NH4Cl white ring from each end.
DISPOSAL / Rinse cotton balls and discard. Rinse glass tube thoroughly.
DISCUSSION / Reaction: NH3 (g) + HCl (g) --> NH4Cl (s) The rate of diffusion of gases is inversely related to the square root of their molecular masses. Since HCl (MM = 36.5) has greater mass than NH3 (MM = 17), the NH3 diffuses more rapidly. The pH paper allows one to see the progress of each gas. An extension of this is to quantitively determine how closely these gases behave with respect to Graham's Law (distance travelled is proportional to diffusion rate if both gases are introduced into the tube at the same time and at the same partial pressures. Don't expect accurate results as maintaining concentrations is difficult.)

Chlorine

Lab. 41: Bleaching Properties of Chlorine

PURPOSE / To demonstrate the bleaching properties of chlorine.
MATERIALS / 10 mL 5% NaClO (Clorox), 100 mL 1M HCl, 250 mL Erlenmeyer flask, glass plate, flower petals of blue or red pigment, red food color, vinegar, Petri dish.
HAZARDS / Cl2 is a noxious gas, use well-ventilated hood. The gas irritates eyes; if inhaled, can cause lung irritation; in high concentration is irritating to the skin. Cl2 is a strong oxidizing agent: combustible materials may burn in it; acetylene may form an explosive mixture.
PROCEDURE / Pour 100 mL of 1.0 M HCl into the flask. Add 10 mL of 5% NaClO. Cover with the glass plate. Within a minute the flask should fill with yellow-green Cl2 gas. Suspend the flower petals in the flask and observe results. Pour enough water in Petri dish to cover bottom. Add 10 drops of red food color and stir. Add 3 mL of clorox to the solution and observe for about 20 sec. Add a few drops of vinegar and observe.
DISPOSAL / Dilute the solution before flushing down the drain. Wash containers with soap and water.
DISCUSSION / Chlorine is a yellow-green gas with a suffocating odor. It has the ability to bleach certain fabrics such as indigo dye in blue jeans and the pigments in some flowers (blue delphiniums give a nice result). The chlorine oxidizes the red food color over a long period of time. The result is more dramatic with the addition of vinegar. See Shakhashiri, Vol. 2, pp. 220-227 for others.

Lab. 44: Combustion of Chlorine and Hydrogen