Question

Scenario: You are an engineer supervising the work on a brownfield remediation project. Just before the close of business, as you are grabbing your coat, you notice one of your coworkers left some stock solutions out on the bench. Thinking you can quickly put them away and then go home, you walk over to do so, but you discover instead that the labels have not been put on the stock containers. There are labels on the counter, in front of the containers, but they have not been printed yet. There are four colorless glass containers, two of which contain a clear, colorless solution. The other two solutions have a dark bluish-green color. Over to the right are a number of containers that had been used recently. These containers contain chemical compounds, in solid form, that are commonly used in your lab. They are: barium nitrate, nickel (II) chloride, potassium nitrite, iron (III) nitrate, lithium sulfate, aluminum nitrate, sodium bromide, lead (II) chloride, calcium nitrate and magnesium fluoride. Can you identify the contents of the containers and put correct labels on the containers? Design a flowchart to show how you would test the solutions to determine what they might be. The flowchart must clearly list the chemicals needed for each test as well as show the expected test results.

Answer 1

Considering the colour of the solutions, it is the cations which impart clur to the solution. so, talking about the colour, only nickel gives a bluish green solution and Iron(III) gives yellow.

So, the stock slution is not iron(III) nitrate. The other cations form colorless solutions. It is unlikely that any of them are lead(II) chloride or magnesium fluoride, since both are insoluble in water at room temperature.

Then, you can also perform flame test to find out the colours od the corresponding cations:barium (greenish yellow), lithium (red), potassium (purple), calcium (reddish orange) or sodium (yellow).

So, you can confirm the prsence of stock solution by:

aluminum nitrate -- add NaOH to form a gelatinous precip that dissolves with additional OH-
sodium bromide -- yellow flame test
lead (II) chloride -- not present, insoluble
calcium nitrate -- reddish orange flame test
magnesium fluoride -- not present, insolublebarium nitrate -- the addition of H2SO4 will produce a precipitate
nickel (II) chloride -- blue-green in color
potassium nitrite -- purple flame test
iron (III) nitrate -- not present, yellow solution
lithium sulfate -- add some Ba2+ to confirm the presence of SO4^2-