This one is the toughie, after this it should be easier.
Remember, more is not always better. If you add too much reagent or too much unknown you may get a precipitate a step early (if you have over-concentrated you may exceed Ksp of something a step early). This will make a false positive test.
Over diluting and you may not get any precipitate (too dilute to exceed Ksp) this would result in a false negative.
You have 2 chemicals from the Copper/Arsenic group. (No one has Arsenic). This will require procedures 5 through 14 in the instructions.
Procedure 5: Use water at a low boil, a simmering boil, not a blast furnance. You can overcook, or "burn" your precipitates. After centrifuging, you may dispose of the decantate if you are working on Unknown 3. When you arrive back here on Unknown 6, you must save the decantate.
Mr. K recycles all chemicals so do not dispose of your unknown until you know which waste container to put it into.