OBJECTIVE
Identify six unknown ionic salt  solution based  on their reactions.
Write the chemical equations for the ocurring reactions and identify the products.

INTRODUCTION
Certain clues may lead chemists to identification of a solute in a solution. Such characteristics are  color, odor, viscosity, acidity, and other properties of that solution. Mixing the solution of unknown identity  with another solution can bring additional information through the observation of the occurring process: precipitate formation and its color and texture, gas evolution, heat absorption or evolution. Some of the reactions are characteristic for certain ions only, thus facilitating the identification of the cation and the anion in an unknown solution on an ionic compound.
The information about  the solubility in water of a certain ionic compound may also  be obtained by mixing two solutions: one containing the cation of the compound in question and the other the anion. The formation of a precipitate as a result of a double displacement reaction will indicate that the compound in question is indeed insoluble.
In this experiment you will study the reactions  of six aqueous solutions of known ionic compounds by mixing them in pairs
(total of 15 different pairs). Solutions used are: AgNO₃, Na₂CO₃, HCl, NaOH, Na₃PO_4, and FeCl_{3 .}
You will  record as much of the information about the occurring reaction as possible (color of the solutions before and after the reaction, precipitate formed, color and texture of the ppt,  gas formed , etc.).
The observations have to be  meticulously recorded.  You may  use abbreviations to describe   the reaction results. The acceptable abbreviations used to record your observations are: sln for solution,  NR for no reaction, ppt for precipitate, wppt for white precipitate, rppt for red ppt , etc.
You will also receive a set of six unknown solutions which are  the same solutions as the knowns  but labeled with a letter code instead of the chemical name. You will mix the unknown  solutions in pairs and record the results in a separate table.
Your goal is to identify all six unknown solutions, which means to  assign a chemical formula to each  unknown code (e.g. A is NaCl).
The  identification is based on the comparison of the data recorded in the “unknown” part of the experiment with  the results from the “known” part of the experiment.

Example
Please refer to Table 1 and 2  for an example of a data tables for 5 known solutions and  5 unknown solutions.
In this case,  the identity of the solution A  can be confirmed as AgNO₃  becuase it was the only solution to form   . The yellow precipitate is formed when mixing AgNO₃ and  KI as well as a result of mixing  solution B and solution A. A is silver nitrate, therefore, B is KI. The similar deduction process (actually show it in the postlab  q#1)  leads to the identification of solution C as HCl and solution E as Na₂CO₃. By elimination and comparison of  the texture and color of the formed ppt (describe it) with the known results D could be  identified as Na₂SO₄.

Table 1. Mixed Pairs of Known Solutions					Table 2. Mixed Pairs of Unknown Solutions
	Na2CO3	Na2SO4	HCl	AgNO3		A	B	C	D
KI	NR	wppt, milky, light,  small amount	NR	yellow ppt small particle	E	cream ppt curd-like, heavy	NR	bubbles, no odor, color	NR
AgNO3	cream ppt curd-like	NR	wppt, curd-like later purple		D	wppt, light, small amount	NR	NR
HCl	bubbles, odorless, colorless	NR			C	wppt, curd-like; purple after some time	NR
Na2SO4	NR				B	yellow ppt small particle

PROCEDURE
Safety !!!!!
Hydrochloric acid, HCl - corrosive and toxic;
silver nitrate, AgNO₃- highly toxic and oxidant ;
sodium hydroxide, NaOH- corrosive and toxic.
Be cautious and wear you safety glasses at all times!!!

IMPORTANT NOTES
1)If cloudiness, milkiness, or turbidity is  observed after mixing two clear (not necessarily colorless) solutions, it  means that a precipitate was formed. A precipitate does not always  mean chunks of solid, it may also  be more of a gelatinous mass giving the impression of the change in thickness of the solution, or very small particles suspended in the solution making the solutions look milky.Make sure that your observations record includes textures and types  of precipitates formed, not only the color
(e.g. off-white ppt, cottage cheese-like, curdling, smooth, milky, heavy, light, etc.).

2)  Some of the reactions occur very  fast and some more slowly. Make sure that you observe the reaction from the start and  for about 1 minute and record the observations. However, the gas evolution  is immediate, so you need to be prepared for early detection of the bubbles formed ( there may no be very conspicuous with a colorless gas)

3) Make sure that you always use the pipet dedicated to a given solution and never dip  the tip of the pipet into the solution in the well. Cross-contamination with foreign  chemical material may produce side reactions  with unexpected and confusing results, which may prevent you from proper identification of the unknown.

KNOWN SOLUTIONS
1. Label six small, clean and dry, test tubes to reflect the names of six known solutions.

2. Obtain about 1 ml of each solution in the labeled test tubes. No more than 1 ml. You can always take more later if you need it.

3. Obtain six  clean and dry plastic transfer pipets. Place each pipet in the test tube with the corresponding solution.
As long as you are working with one solution at a time and replace the pipet in the test tube, you will not  need to label the pipets.

4. Prepare a clean and dry spot plate.

5. Using the designated pipet,  transfer  3 drops of this first known solutions  in the label column in  your data table to the first 5 wells of the plate  (e.g. KI  if  the compounds from Table 1 in the introduction were used). You only need 5 wells  because you will not be adding the solution that already is in the well to itself (you won’t be mixing NaCl with NaCl!).

6. Using a designated pipet, add 3 drops  of the next solution,  crossing paths with the first in your data table (e.g. Na₂CO₃  if  the compounds from Table 1 in the introduction were used). If necessary, mix solutions with a  provided plastic stirrer, rinsing
(using  a squirt bottle) and drying (paper towel)  the stirrer after each use.   Record your observations.

7.  To the second of the five wells containing  the first solution, add  the next solution on your data sheet, crossing paths with the first (e.g. Na₂SO₄ if  the compounds from Table 1 in the introduction were used). Record the observations.

8. Continue in this manner  until all available solutions  ( across the table) were mixed into the five wells containig the first solution (from the first column).

9.  Clean the plate (if necessary) and repeat  steps 1-8  for all solutions down the first column of the data table, mixing them with the solutions across the table, until 15 different pairs of solutions have been mixed and the results recorded.

UNKNOWN SOLUTIONS
Obtain new set of six clean and dry  pipets and clean and dry test tubes.
Repeat the steps as for the  KNOWN solutions  but use the unknown solutions coded with  letters: A through F. Record all observations.

CLEANUP
When you are done, clean the well plates and  rinse all 12 pipets in the following manner:
1. Expel any remaining solution from the pipet into the waste container.
2. Pour distilled water into three small test tubes.
3. Draw some water from the first test tube with a pipet to be rinsed, invert it, shake with water in the bulb, then  discard the water into the waste container.
4. Draw some water from the second test tube and discard, invert the pipet, shake, and discard the rinse.
5. Repeat with the third test tube.
6. Return the plates and the  pipets to the instructor.

PRELAB  (click  to go to prelab file)

POSTLAB (click  to go to postlab file)