Possible ions present:
Cations: K+, Nh4+, Na+
Anions: OH-, Cl-, HSO4-/SO42-, HCO3-/CO32-, NO3-
Part One: determine pH
To determine pH, I will take a small portion of the unknown sample and make it into a solution using neutral water. Next, I will determine the pH by testing the pH with colorimetric indicators and using my Table of Acid/Base Reactions sheet from my lab manual as a guide.
Part Two: determine cations in a mixture of salts
NH4+: This is the ONLY cation that tested positive for a “Damp Red Litmus Paper” test. To perform this test, take a portion of your unknown solution made from the unknown sample and place 2 mL of 0.01M of unknown solution into a test tube. Next, add 1mL of 6M NaOH solution to the test tube and gently warm it with a Bunsen burner. Then suspended a damp red litmus paper over the test tube. If the litmus paper changes to blue, then there are NH4+ ions present.
Do a crucible test where you add a solid sample of unknown into a crucible and heat it strongly with no lid. If smoke is produced then there are NH4+ ions present.
Na+: To test for Na+ ions, do a Flame Test. First, take some Nichrome wire and make a small loop at the end of the wire and cork the other end of the wire. Clean the wire by using 16M HNO3 acid then rinse it with deionized water. Next, heat the wire in a blue Bunsen burner flame until it gets red hot. Place a small piece of the solid unknown sample onto the loop of the wire and heat it. Observe the flame. If a violet flame is seen then K+ ions are present or if orange-yellow then Na+ ions present.
K+: To test for K+ ions, take some solid unknown sample and perform the Crucible Test again to eliminate any interference from NH4+. Let crucible cool (come back to experiment if needed) then place liquid into a small test tube. Transfer 10 drops of the liquid unknown sample into a medium test tube and add 2 drops of 1M HOAc/NAOAc buffer. Next, add 5 drops of 0.08M sodium cobaltinitrite and let it stand for a few minutes. If a yellow-orange precipitate forms then K+ ions are present.
END OF CATION TESTS
Part Three: determine anions in a mixture of salts
NO3-: To test for NO3- ions, do a Watch Glass Crystal Test. Place several small crystals of Fe(H2O)6(NH4)2(SO4)2 in the center of a watch glass. Cover the crystals with the unknown solution and add several drops