Discovering the Mystery of Eleven Test Tubes

Abstract

Eleven mystery test tubes labeled from K-1 to K-11 contained: 6M H2SO4, 6M NH3, 6M HCl, 6M NaOH, 1M NaCl, 1M Fe(NO3)3, 1M NiSO4, 1M AgNO3, 1M KSCN, 1M Ba(NO3)2, 1M Cu(NO3)2 respectively. The contents of the test tubes were determined by chemical experiments. Solution K-1 contained NiSO4 because when solution K-9, ammonia which was identified by its pungent odor, was added, an inky dark blue color was made.

Iron (Fe (NO3)3) was determined to be in test tube K-2. KSCN was found in test tube K-11 since Fe (NO3)3 and KSCN makes a bloody color when mixed together. Flame tests were conducted in which K-8 burned green which identifies Cu(NO3)2, and the solution from test K-10 burned yellow orange which indicates NaCl. Solution from test tube K-5 turned red litmus paper to blue which indicates a strong base (NaOH). Solutions in test tubes K-4 and K-6 are both strong acids which turned blue litmus paper to blue.

Silver nitrate (K-7) produces precipitate with both acids and Barium nitrate can only produce precipitate with H2SO4 and it remains clear in HCl, K-3 precipitated with K-4 but did nothing with K-6, which proves that K-4 is H2SO4 and K-6 is HCl.

Introduction

Water has many unique chemical and physical properties. Water goes through various reactions and possesses unusual properties to sustain life on Earth. Water has the ability to dissolve a wide variety of substances. Therefore, in nature, water has a variety of dissolved substances such as different elements, salts, gases.

Any solution in which water is solvent is called aqueous solutions. Most aqueous solutions share the same chemical and physical characteristics, which makes it very difficult to identify without conducting various chemical tests. For determining the identity of unknown chemical solutions, it is important to understand the solubility and insolubility rules such as: precipitation, change in color, pH testing, litmus paper test, and flame test. There are different solubility and insolubility rules for all ionic compounds.

All cations in group A1 (Li+, Na+, K+, etc), ammonium cation (NH4+), acetates (CH3COO-), most perchlorates (ClO4-) , and all common nitrates (NO3-) are soluble. All common iodides (I-), bromides (Br-), chlorides (Cl-), fluorides (F-) are soluble, except Hg22+, Cu+, Pb2+, Ag+ and those of Group 2A (2). All the sulfates (SO42-) except Ca2+, Sr2+, Ba2+, Ag+, and Pb2+ are soluble. Except those of Group 1A (1), ammonium (NH4+), and the larger members of Group 2A (2), all the common metal hydroxides, common carbonates (CO32-), common phosphates (PO43-) and all common sulfides (SO42-) are insoluble .

In a precipitation reaction, a precipitate forms which is an insoluble product formed from the two soluble ionic compounds reaction. Precipitation reactions are very common in nature and industries. Most of the deep-sea structures like hydrothermal vents are formed as result of this kind of chemical process. Most industries use precipitation reaction to produce inorganic compounds. Litmus paper is used to identify if a substance is acidic or basic. There are different types of litmus paper.

Red litmus paper which turns blue in the presence of a base and blue litmus paper which turns pink in the presence of an acid were used in this experiment. In this experiment eleven test tubes containing unknown solutions were provided. Which test tube containe H2SO4, NH3, HCl, NaOH, NaCl, Fe(NO3)3, NiSO4, AgNO3, KSCN, Ba(NO3)2, and Cu(NO3)2 were indentified. Some information was given about the reactions of all these aqueous solutions in the eleven test tubes as following:

1. H2SO4, sulfuric acid reacts with metals and produces insoluble sulfates; it is strong acid and counted as the most powerful industrial chemical in the world.
2. NH3, ammonia is used as fertilizer and it is stinky like household cleaner
3. HCl, it is strong acid and when blended with ammonia, it produces a dense insoluble chloride fog.
4. NaOH, sodium hydroxide is a strong base. It reacts with HCl and forms NaCl and H2O.
5. NaCl, sodium chloride, is a common salt and it burns in the flame test.
6. Fe (NO3)3, Ferric nitrate, is much more active than ferrous. It could be identified by its reddish color and when mixed with thiocyanate, it reveals a “bloody” red color.
7. NiSO4, nickel sulfate was in the past very valuable and it is recognized by its “envious” green nature.
8. AgNO3, silver (I) nitrate is one of the most rare and valuable substances known in the world. It actively participates in reactions with halides and pseudo halides.
9. KSCN, potassium thiocyanate is poisonous to amphibians. It makes a “bloody” red color when put in reaction with iron.
10. Ba (NO3)2, barium nitrate produces pale precipitate when put in reaction with sulfuric acid.
11. Cu (NO3)2, cupric nitrate is used widely in industries. It makes an impersonate ink when mixed with ammonia.

Method and Materials

Solutions of 6M H2SO4, 6M NH3, 6M HCl, 6M NaOH, and 1. 0 M of NaCl, 1M Fe(NO3)3, 1M NiSO4, 1M AgNO3, 1M KSCN, 1M Ba(NO3)2, and 1M Cu(NO3)2 were given in separate test tubes. The color of possible precipitates, ions, acid-base behaviour, odor and solubility rules were conducted. The key information about a mixture of two solutions was put in the Table 1 as NR for no reaction, ppt for precipitate, Heat for evolving heat, Gas for gas if evolved and Cc for color changes.

In the lab, eleven test tubes containing unidentified solutions were obtained. To indentify the unknown solutions, about two or three drops of the solution from one test tube was mixed in a depression of the spot plate with two or three drops of the solution from another test tube. The mixing of two solutions from two different test tubes was continued untill the tests were positive. Color changes, precipitate formation, smoke, heat, and odor of all the mixed solutions were observed and noted.

Ppt stands for that the two solutions precipitate when mixed with each other, Cc stands for changing color, and X stands for nothing occurs between the two solutions.

Results

By following the solubility rules and other characteristics of the solutions and the mystery solutions were mixed together and were identified. K-1 test tube contained NiSO4 because it made and inky dark blue color with solution from test tube K-9, ammonia which was identified by its pungent odor. Iron was identified from its reddish yellow color in test tube K-2. After mixing iron with solution of all unidentified test tubes, KSCN was found in test tube K-11 since iron and KSCN makes a bloody red color when mixed together.

Solution from test tube K-8 burned into green flame which identifies Cu(NO3)2, and the solution from test K-10 burned into yellow orange flame under flame test which indicates NaCl. Solution from test tube K-5 turned red litmus paper to blue which is the only strong base NaOH . Solutions in test tubes K-4 and K-6 are both strong acid which turned blue litmus paper to blue. Silver produces precipitate with both acids which was in test tube K-7. Barium nitrate can only produce precipitate with H2SO4 and it dissolves in HCl.

Solution from K-3 precipitated with H2SO4 (K-4) but dissolved with K-6, which proves that K-4 is H2SO4 and K-6 is HCl.

Discussion

The eleven mystery test tubes set which was given was set “K”. The test tubes where labeled K-1 through K-11. Ammonia was identified first from its stinky household cleaner smell which was test tube K-9. The ferric nitrate or iron had a reddish yellow color which was the only test tube had this color was identified in test tube K-2.

Sodium chloride (NaCl) and NiSO4 burns orange and green respectively in the flame test. The solutions from test tube K-3, K-1, and K-10 burned bright yellow, green, and orange yellow respectively. The flame test indicated that the solution in K-1 is NiSO4 and the solution in K-10 is NaCl. Ammonia makes a dark blue inky color when mixed with Cu (NO3)3, so for determining cupric nitrate ammonia was mixed with K-8, K-7, and K-10. Mixing solutions together resulted in the following: K-8 and ammonia made a dark blue inky color, K-7 and ammonia made a brownish color, and K-10 and ammonia showed nothing but a clear solution.

From this mixing it appeared that K-8 is cupric nitrate, Cu (NO3)2. Iron makes a bloody color when mixed with potassium thiocyanate, so to find the potassium thiocyanate we mixed iron with remaining unidentified solutions. Potassium thiocyanate was in test tube K-11. The net ionic reaction for iron and thiocyanate is as following: Fe+3 (aq) + 3SCN- Fe (SCN) 3 The information that was given prior to the experiment mentioned that there are two strong acids and a strong base among the eleven mystery test tube.

The strong base NaOH was indentified quickly with litmus paper test. NaOH which was in test tube K-5 turned the red litmus to blue. Ammonia was actually ammonium hydroxide so there were two strong bases. Both acids were identified with litmus test in test tube K-4 and K-6, but it was not clear yet which test tube contains which acid. According to known information that was gathered ammonia makes fog in the head when it is close to HCl, but ammonia did not make a fog with any of the two acid test tubes.

Silver (I) nitrate produces precipitates with HCl and H2SO4, and Ba(NO3)2 produces precipitate only with H2SO4. The net ionic reaction silver (I) nitrate with HCl and H2SO4 and Ba(NO3)2 with H2SO4 are as following: Ag+ (aq) + Cl – (aq) AgCl (aq) 2Ag+ (aq) + SO4- (aq) Ag2 (SO4) (aq) Ba+3 (aq) + SO4- (aq) BaSO4 (aq) So the remaining test tubes K-3 and K-7 were mixed with two acids from test tubes K-4 and K-6 to identified silver (I) nitrate, Barium nitrate, HCl and H2SO4.

The result shows that K-3 is barium nitrate, K-7 is silver (I) nitrate, K-4 is H2SO4 and K-6 is HCl.

Conclusion

The solutions in the test tubes were as following: Test tube #| Identity of solutions| K1| NiSO4| K2| Fe (NO3)3| K3| Ba (NO3)2| K4| H2SO4| K5| NaOH| K6| HCl| K7| AgNO3| K8| Cu (NO3)2| K9| NH3| K10| NaCl| K11| KSCN|

Citation

1. “Aqueous Solutions: The 12 Test Tube Mystery, C12-1-07. UNIVERSITY OF MANITOBA May 18, 2008
2. Martin S. Silberberg. “Mixtures: classification and Separation. ” Chemistry: The Molecular Nature of matter and change 4th Ed New York: McGraw-Hill; 2006. P 143.
3. Rock Creek Chemistry Department. “Lab 23 – The Mystery of The Eleven Test Tubes” Ch 223 Labs [Rock Creek Only] Portland: PCC; 2003