Qualitative analysis of ionic compounds
background [prelab assignment (20 points) due at the beginning of the lab]
if a precipitate forms by mixing the following chemicals in the corresponding row & column, then write "ppt" in the appropriate cell in the below table
silver nitrate lead II nitrate cobalt II nitrate copper II nitrate barium nitrate iron III nitrate magnesium nitrate use the above table in your prelab assignment & lab note book.
pick 3 chemicals below (see materials section) - one from each column - then design an experiment to identify your unknown ionic samples (from the 8 remaining choices) based on the absence / presence of a precipitate (or color of the solution) without using more than 3 of the known solutions shown in the above table. include implication / consequence of observations.
purpose
evaluate the reliability of the solubility rules
identify the unknown ionic compound in 3 samples based upon their reaction with other known solutions using solubility rules
materials
known aqueous solution (~ 0.1 M) of the chemicals shown in the above table
unknown aqueous solution; possibilities are shown below. There may be zero, one, or more than one choice from each column.
BaCl2 CuCl2 Na2CO3 Ba(OH)2 Cu(NO3)2 NaI CuSO4 NaOH Na2SO4 microwell plates [to view reaction]
methods / data analysis
student design: no more than 3 additions of a known solution per unknown ionic compound to identify it.
if a precipitate does not form within a second or so upon adding the 2nd solution, consider it to be not forming a precipitate. record any color of the precipitate - it *might* be on the ap exam.
Content of lab report [ 30 points; no revision for this lab report ]
data / observations (10 points)
using a table, compare your predictions based on the solubility rules (i.e. ppt vs. no ppt) versus your experimental observations (ppt, no ppt, or cloudy, i.e. opaque, transparent, or translucent, respectively). state frequency (i.e. %) of agreement, disagreement, & ambiguous situations.
results of mixing various pairs of known and unknown solutions
data analysis: (20 points)
based on the preceding table, what is the reliability of the solubility rules; elaborate, e.g. if the solubility rule is not good, then is it due to the frequency of disagreements ? ambiguous situations ?
identify the ionic compound in your 3 unknown samples; justify your answers, based on your observations.
selected links
example basis to identify cation & anion
simulation of experimental protocol to identify ions (see applets for "qualitative analysis of cation / anion)
lab activity source (examples): site 1 & site 2 [access 4 / 2009]