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 containe rs 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?

1. 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.

2. If you were actually confronted with this situation, would you put labels on the containers or would you dispose of the solu tions? Explain your answer.

Answer 1

Solution.

Among barium nitrate, nickel (II) chloride, potassium nitrite, iron (III) nitrate, lithium sulfate, aluminum nitrate, sodium bromide, lead (II) chloride, calcium nitrate and magnesium fluoride, only nickel (II) chloride has a green color.

Therefore, the colored solutions should be tested for the presence of Ni²⁺ ions and Fe³⁺. A colorless solution can contain Al salt, its analysis is given below as well.

The non-colored solutions can also contain Ba²⁺, NO₂^-, SO₄^2- Br-, Ca²⁺, Mg²⁺, Pb²⁺.

Clean the platinum wire by dipping it in HCl taken in a watch glass and then heat it strongly in the flame. Place a small amount of the solution and introduce it into the flame. Note the color imparted to the flame.

Brick - red (not persistent)    Ca²⁺

Grassy - green (Persistent)    Ba²⁺

Dull bluish - white    Pb²⁺

Mg²⁺ ions can be discovered by using a magneson dye (blue in the presence of these ions).

The sulfate ions can be discovered using a BaCl₂ solution (white precipitate), and the nitrite-ions by means of oxidation by a potassium permanganate (fading).

2. If I am actually confronted with this situation, I will dispose of all the unidentified solutions, according to the occupational safety and health rules and regulations.