Table 1: Known Solutions Bottle Numbers No. Reactant Formula Molarity

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1 Eric Dammer Dr. Arnold Chemistry II February 16, 2001 Qualitative Analysis of Unknown Solutions Abstract: Eleven unknown solutions are determined by qualitative analysis using the same set of known solutions. Predictions are tested in a control; experimental solution results are compared to the control results as well as predictions, allowing for induction of the most likely reactant in each unknown solution. Introduction: Given known solutions are listed in table 1. There are 11 unknown solutions in marked bottles labeled A through K. Each unknown corresponds to one known solution. Table 1: Known Solutions Bottle Numbers No. Reactant Formula Molarity Acetic Acid Ammonium Chloride Barium Nitrate Calcium Chloride Hydrochloric Acid Silver Nitrate Sodium Bicarbonate Sodium Carbonate Trisodium Phosphate Sodium Sulfate Sulfuric Acid CH 3 COOH NH 4 Cl Ba(NO 3 ) 2 CaCl 2 HCl AgNO 3 NaHCO 3 Na 2 CO 3 Na 3 PO 4 Na 2 SO 4 H 2 SO 4 0.2M 0.2M 2.5M In the experiment, each unknown is reacted with each known in a plastic well, one of many in a matrix of small wells. Of the total 121 (11²) possible combinations, only half are unique because one reactant added to another in equal quantity should produce the same products; some products may remain on the surface or bottom depending on the comparative density of the added solution in each experimental well. Only 22 reactions are predicted to have observable products, regardless of where they form in solution: NaHCO 3 (aq) + CH 3 COOH (aq) NaCH 3 COO (aq) + H 2 O (l) + CO 2 (g) [1-7] CH 3 COOH (aq) + Na 2 CO 3 (aq) NaCH 3 COO (aq) + NaOH (aq) + CO 2 (g) [1-8] AgNO 3 (aq) + NH 4 Cl (aq) AgCl (s) + NH 4 NO 3 (aq) [2-6] 3Ba(NO 3 ) 2 (aq) + 2Na 3 PO 4 (aq) Ba 3 (PO 4 ) 2 (s) + 6NaNO 3 (aq) [3-4] Ba(NO 3 ) 2 (aq) + 2NaHCO 3 (aq) BaHCO 3 (s) + 2NaNO 3 (aq) [3-7] Na 2 CO 3 (aq) + Ba(NO 3 ) 2 (aq) BaCO 3 (s) + 2NaNO 3 (aq) [3-8] 3Ba(NO 3 ) 2 (aq) + 2Na 3 PO 4 (aq) Ba 3 (PO 4 ) 2 (s) + 6NaNO 3 (aq) [3-9] Ba(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) BaSO 4 (s) + 2NaNO 3 (aq) [3-10] Equations continue on page 2.

2 Ba(NO 3 ) 2 (aq) + H 2 SO 4 (aq) BaSO 4 (s) + 2HNO 3 (aq) [3-11] 2AgNO 3 (aq) + CaCl 2 (aq) 2AgCl (s) + Ca(NO 3 ) 2 (aq) [4-6] 2NaHCO 3 (aq) + CaCl 2 (aq) CaCO 3 (s) + 2NaCl (aq) + H 2 O (l) + CO 2 (g) [4-7] CaCl 2 (aq) + Na 2 CO 3 (aq) CaCO 3 (s) + 2NaCl (aq) [4-8] Na 3 PO 4 (aq) + 3CaCl 2 (aq) 6NaCl (aq) + Ca 3 (PO 4 ) 2 (s) [4-9] Na 2 SO 4 (aq) + CaCl 2 (aq) CaSO 4 (s) + 2NaCl (aq) [4-10] AgNO 3 (aq) + HCl (aq) AgCl (s) + 2NaNO 3 (aq) [5-6] NaHCO 3 (aq) + HCl (aq) NaCl (aq) + H 2 O (l) + CO 2 (g) [5-7] Na 2 CO 3 (aq) + HCl (aq) NaCl (aq) + CO 2 (g) + NaOH (aq) [5-8] NaHCO 3 (aq) + AgNO 3 (aq) AgHCO 3 (s) + NaNO 3 (aq) [6-7] 2AgNO 3 (aq) + Na 2 CO 3 (aq) Ag 2 CO 3 (s) + 2NaNO 3 (aq) [6-8] 3AgNO 3 (aq) + Na 3 PO 4 (aq) Ag 3 PO 4 (s) + 3NaNO 3 (aq) [6-9] 2NaHCO 3 (aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2H 2 O (l) + 2CO 2 (g) [7-11] H 2 SO 4 (aq) + Na 2 CO 3 (aq) Na 2 SO 4 (aq) + H 2 O (l) + CO 2 (g) [8-11] Each reaction should occur twice in the experiment, as the known reacts with unknown, and the unknown that corresponds to the same known reacts with the known that corresponds to the same unknown. Thus, 44 wells with visible products are expected to be directly observed. Reactions that give carbon dioxide as a product assume equilibrium of the following reaction, with excess gas escaping from the saturated solution at the reaction temperature. The implications of this buffer are discussed in detail in the results section. H 2 O (l) + CO 2 (g) H 2 CO 3 (aq) H + (aq) + HCO 3 - (aq) [Equation 1.] Results are interpreted to allow inductive reasoning regarding the correspondence of each unknown solution to one of the known solutions. Method: Corning plastic reaction well matrices are thoroughly cleaned and dried before use and each reuse. Pipettes used for unknown and known solutions are to be labeled and are not to be interchanged. Results are shown in table 2. Control results are shown in table 3, where each full column of reactions can be extrapolated from the "L" formed by the column and row, reflected on the diagonal cell which represents null combinations of the same solution. Results: Table 2: Observations of Known Solutions Reacting with Unknown Solutions A adheres to well B slowforming instantly formed

3 D /jell E Slow deposit of crystals F small clumps on surface ; /jell G H /jell bright yellow I J K C slowforming Quickforming ; audible fizz thick particles /jelly; beige clear crystal on surface Small clumps Light yellow thick light beige Yellow pop returning to clear solution rapidly forming It is noteworthy that certain rows expected to exactly correspond to columns extrapolated in table 3 (below) do not while others do. Exact matches are visible as one searches table 3 columns finding matches to the table 2 rows E, F, H, I, J, and K. (See conclusions to check the column numbers found*.) Table 3: Control Reactions of Known Solutions thin 4 dark light 5 / 1 Fizz ( ) 2 clear crystal slowforming /jell anhydrous crystals 6 light yellow beige bright yellow 7 fizz

4 In reactions involving either the unknown or the known solution containing sodium carbonate, equation 1 is a factor in whether product is visible as gas. K (sodium bicarbonate) or It thus follows that Calcium sulfate is borderline soluble (2.4 x 10-5 solubility product). Therefore, these crystals formed slowly as the reaction producing it (equation 4-10) approached equilibrium. The reaction producing clear crystals of calcium carbonate (control reaction 4-8) also posed a problem in that the crystal was clear, singular, and floating (perhaps by surface tension) in only one of the experimental product solutions (F8). The other experimental solutions involving the same product actually developed a (F7, K4), or no crystal(s) at all (this turns out to be D4). The control reaction (4-7) shows the but no carbon dioxide or any gas. Carbonic acid plays a role in whether a product involving carbonate is found or not, and whether gas is released.. In reactions involving sodium carbonate (solution 8) and any one of solutions 1, 3, 4, 5, 6, or 11, carbon dioxide is released into solution as shown in the corresponding equations. Because gas was not observed as a product from most combinations involving these solutions (specifically reactions 1-8, 3-8, 4-8, 5-8, and 8-11), another means to measure of products was required. Referring to equation 1, it becomes apparent that these solutions should be more acidic, just as product solutions containing bicarbonate ions should be more basic. Table 4 column 8 shows the buffer effect of carbonate ion oxidation in solution: appeared on the indicator paper in a wide range when dipped into the unmixed solution (This occurs to a lesser degree in column 7, corresponding to sodium bicarbonate). If unknown solution D is indeed the same as known solution 8, then cells D1, D4, D5, and D11 should confirm this prediction by being basic or more basic than expected. Indeed, all but D4 are strongly basic. (D4 must form calcium carbonate that remains in solution or super-saturated solution) Table 4: Measured of Some Product Solutions Solutions A B C D As labeled E1) E3) 5.0 F1) H1) 12.0 I2) 5.0 J7) K10) 8.0

5 Conclusions: *First, unknown rows in table 2 corresponding to table 3 control columns exactly are E, F, H, J, and K. These are correspond to known solutions 10, 4, 9, 6, and 7 respectively. Thus unknown E contains sodium sulfate, F contains calcium chloride, H contains trisodium phosphate, I contains ammonium chloride, J contains silver nitrate, and K is a sodium bicarbonate solution. Of the remaining solutions, examining makes it clear that D is known solution 8, sodium carbonate. In turn, other unknown solutions with determination dependent on reaction with known solution 8 become apparent: C corresponds to 1 (acetic acid); G is solution 3 (barium nitrate), A is solution 5 (hydrochloric acid), and B is solution 11 (sulfuric acid). All data in both tables 1 and 2 support these conclusions with no contradiction.