Lesson 5: Separating Mixtures of Ions Unit 3: Solubility Lesson 5: Separating Mixtures of Ions

Today’s Example Question A solution contains one or more of Ag+, Ba2+ and Ni2+. Design an experimental procedure to determine which of these cations are present. (We’ll be solving this slowly, over the next few slides.) Copy onto chalkboard.

First, set up a table of solubilities. List the possible ions in the solution as row headings, and list the possible ions that could be added to make precipitates as column headings. Cl- SO42- S2- OH- PO43- Ag+ Ba2+ Ni2+ Have students fill in table before going over it – 5 min Also, copy table onto blackboard for future reference.

Then design a procedure... Step 1: To 1 mL of a solution that may contain Ag+, Ba2+ and/or Ni2+, add a few drops of 1 M NaCl solution. If there is no precipitate, then Ag+ is absent. Proceed to Step 2. If there is a precipitate, then Ag+ is present. Filter off and discard the precipitate. Proceed to Step 2.

Step 2: To the solution from Step 1, add a few drops of 1 M Na2SO4 solution. If there is no precipitate, then Ba2+ is absent. Proceed to Step 3. If there is a precipitate, then Ba2+ is present. Filter off and discard the precipitate. Proceed to Step 3.

Step 3: To the solution from Step 2, add a few drops of 1 M NaOH solution. If there is no precipitate, then Ni2+ is absent. If there is a precipitate, then Ni2+ is present.

Brain Break – Spot 15 Differences!

Qualitative and Quantitative Analysis The procedure we just developed simply tells us which ions are present – this is a qualitative analysis. We may also want to determine how much of each ion is present – a quantitative analysis. This can be done by drying the removed precipitate in each step and determining its mass, which can then be used to calculate the original concentration of the ion in the solution.

Practice Pg. 90 #29, 33, and 36-39 15 min