Color Scheme for Unknowns
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Scheme for Unknowns
Describe each of the unknowns including color, odor, phase, and solubility
Perform a flame test on each unknown
i) Purple flame: K+ is present; NH4+ may also be present
ii) Orange Flame: Na+ is present; K+ and NH4+ may also be present
iii) Red Flame: Ca2+ present; Na+ is not present
iv) no color change: possibly NH4+ present; K+, and Na+ are not
present
Test each unknown for its pH. This can be done by adding small amount of neutral water and placing the solution in separate vials then use indicators to test for its pH.
Around 13; OH- is present
Around 10-12; CO3^2-
Around 9-10; HCO3^-
Around 7; SO4^2-, Cl-, NO3^-, SO4^2-, K+, CA2+ could all be present
Around 5-6 ; NH4+ and/ or Mg(OH2)6^2+
Around 3-3.5; Al(OH2)6^3+
Around 2.5; SO4^2-
viii)
Around 1.5; HSO4
4)Test for NH4+
i) if pH results are acidic then there is a possibility that NH4+ is present
Place around 1-2 milliliters of the unknown solution into vial and then add the same amount of 1M NaOH to produce NH3
Hold wet red litmus paper above the vial and if it turns blue it means that basic NH3 has formed and NH4+ is present. This can also be supported by the smell NH3 gives off.
5)Test for K+
If substance tested positive for NH4+ it must be removed before testing for K+
Place the substance in a crucible and heat over a burner until fumes and smoke are no longer being discharged.
At this point no NH4+ should be in the crucible. Dissolve the remaining substance into about 2 milliliters of deionized water.
Add 1 drop of 6M HAc and about 3 drops of cobaltinitrate reagent to the substance.
If a yellow precipitate is formed then K+ is present
6)Test for Cl-
i) Place solution in vial and add excess 6M HNO3 until acidic. This