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Color Scheme for Unknowns

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Scheme for Unknowns

1) Describe each of the unknowns including color, odor, phase, and solubility

2) 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

3) Test each unknown for it's 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 it's pH.

i) Around 13; OH- is present

ii) Around 10-12; CO3^2-

iii) Around 9-10; HCO3^-

iv) Around 7; SO4^2-, Cl-, NO3^-, SO4^2-, K+, CA2+ could all be present

v) Around 5-6 ; NH4+ and/ or Mg(OH2)6^2+

vi) Around 3-3.5; Al(OH2)6^3+

vii) 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

ii) Place around 1-2 milliliters of the unknown solution into vial and then add the same amount of 1M NaOH to produce NH3

iii) 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+

i) If substance tested positive for NH4+ it must be removed before testing for K+

ii) Place the substance in a crucible and heat over a burner until fumes and smoke are no longer being discharged.

iii) At this point no NH4+ should be in the crucible. Dissolve the remaining substance into about 2 milliliters of deionized water.

iv) Add 1 drop of 6M HAc and about 3 drops of cobaltinitrate reagent to the substance.

v) 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

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