Chemistry/Analysis of Solutions
The purpose of this experiment is to identify the contents of six bottles. In no particular order, the bottles contain solutions of the following compounds.
- AgNO3 (silver nitrate)
- HCl (hydrochloric acid)
- Na2CO3 (sodium carbonate)
- Pb(NO3)2(lead(II) nitrate)
- NaCl (sodium chloride)
- KI (potassium iodide)
When these chemicals dissolve in water, they produce the ions listed in the table below.
|Chemical||Positive ion produced||Negative ion produced|
When the ions in the above table are mixed, some combinations of ions do nothing while others produce a visible result. The ion combinations that produce a cloudy solid (a PRECIPITATE) or produce a gas (EFFERVESCENCE) are shown in the next table.
|Positive ion||Negative ion||Product||Comments|
|Ag+||Cl–||AgCl||Solid (silver chloride)|
|Ag+||I–||Ag I||Solid (silver iodide)|
|2 Ag+||Ag2CO3||Solid (silver carbonate)|
|Pb2+||2 Cl–||PbCl2||Solid (lead(II) chloride)|
|Pb2+||2 I–||Pb I 2||Solid (lead(II) iodide)|
|Pb2+||PbCO3||Solid (lead (II) carbonate)|
|2H+||H2O + CO2||Water and a gas (carbon dioxide)|
You will be given two sets of bottles. One set is properly labeled so you know which ions are reacting. The second set contains the same compounds as UNKNOWNS with a scrambled order. You will mix every combination of the known set of bottles and record what you see. Then you will mix every combination of the UNKNOWN set of bottles and again record what you see. By comparing the two sets of observations you should be able to identify the contents of each bottle of UNKNOWN solution.
Table I : Results of Mixing KNOWN Solutions
|silver nitrate AgNO3||hydrochloric acid HCl||sodium carbonate Na2CO3||lead (II) nitrate Pb(NO3)2||sodium chloride NaCl||potassium iodide KI|
|silver nitrate AgNO3||1||2||3||4||5|
|hydrochloric acid HCl||1||6||7||8||9|
|sodium carbonate Na2CO3||2||6||10||11||12|
|lead (II) nitrate Pb(NO3)2||3||7||10||13||14|
|sodium chloride NaCl||4||8||11||13||15|
|potassium iodide KI||5||9||12||14||15|
Table II : Results of Mixing UNKNOWN Solutions
|UNKNOWN A||UNKNOWN B||UNKNOWN C||UNKNOWN D||UNKNOWN E||UNKNOWN F|
ANALYSIS OF RESULTS
Compare the observations you recorded in Data Table I to the observations you recorded in Data Table II. Let’s pretend Data Table II shows that mixing solutions A and B produces a blue precipitate and a green gas. If you found that mixing HCl and NaCl gives a blue precipitate and a green gas according to Data Table I (they don’t give that result but, hey, we‘re pretending!), then you know that one of solution A and B is HCl and the other is NaCl. At this point you don’t know which is which. By seeing what other special results are found for solution A and finding similar results in Data Table I, you can eventually decide whether solution A is HCl or NaCl (in our pretend analysis). Continue in this way until you have completely analyzed which solution is which. HINT: The presence of effervescence, the colour of precipitates and the number of precipitates formed by a compound are all important. Good luck and have fun!
1. Show the results of your analysis by filling in the table below.
|Actual Chemical in Solution||UNKNOWN Bottle Label|
2. You have been hired to analyze a water sample. The person bringing you the sample tells you that it is one of the following samples:
but she does not know which sample it is. How could you use the results of adding KI to the water sample to find what is in the sample you have been given? Note: you must be very specific in stating how to analyze the results. For example: “If I see ... then I know that the solution contains ...”
3. Why isn’t it necessary to mix the chemical combinations for the grey squares in Data Table I?
4. Why is it unnecessary to mix BOTH the solutions in the upper triangle of 15 squares AND the lower triangle of 15 squares in Data Table I? In other words, why is it permissible to copy the results from the upper set of 15 squares into the “kitty corner” set of 15 squares below the grey band?