Achievement Standard Chemistry 2.2 (91182)

Carry out procedures to identify ions in solution
Achievement standard:

This achievement standard is assessed via practical test. You are required to identify ions from the following list:
Cations: sodium (by elimination only), magnesium, aluminium, silver, iron II, iron III, copper II, lead, zinc, barium
Anions: nitrate (by elimination only), hydroxide, carbonate, chloride, iodide, sulfate

Note that although only soluble ions from the list above can be assessed, a wider range of ions and ionic substances may be used for teaching purposes so as to improve understanding of the underlying chemistry.

Precipitation
If two dissolved ions which can form something insoluble come into contact, they will react and form the insoluble salt. This will form a small particle of undissolved material suspended in the liquid; this is known as a precipitate.

Ionic substances can be classified as soluble (s), insoluble (i) or weakly soluble (w). Of the ions in the list above, the solubility can be summarized in a table:

Cation
sodium
magnesium
barium
aluminium
iron II
iron III
lead
zinc
copper II
silver
Anion










nitrate
s
s
s
s
s
s
s
s
s
s
chloride
s
s
s
s
s
s
w
s
s
i
iodide
s
s
s
s
s
s
i
s
s
i
sulfate
s
s
i
s
s
s
i
s
s
w
hydroxide
s
w
w
i
i
i
i
i
i
i
carbonate
w
i
i
i
i
i
i
i
i
i
e.g. magnesium carbonate is insoluble, barium chloride is soluble.

If you mix two solutions where one combination of the ions present shows an i on the table above there will be a precipitate (it will usually happen with a "w" also).

For example, if you mix magnesium chloride and silver nitrate you will get a precipitate of silver chloride.
A few of the precipitates are notably coloured and this can identify certain ions. An example is potassium iodide, which is bright yellow.precipitate of lead iodide. This means you can use lead nitrate as a test for iodide ions, or an iodide salt (such as potassium or sodium iodide) as a test for lead ions. Both these tests are a bit more unambiguous than the test given on the NZQA mandated flowchart.

Resources:
SHC students please note that you must be logged into your SHC Google account to access documents stored in Google Drive. These will generally be hyperlinked. The documents showing as an icon should be freely available without needing to be logged on via Google.

visitors from other schools please note that the hyperlinked documents are only available to SHC students for reasons related to copyright licensing.

Text resource and exercises 1





On the sheet below, the answers are there but in white font. To see them, open via an app (e.g. Notability) that allows you to change the background (paper) colour electronically.



Below is a table of ALL reactions on the flowchart/student resource