CHM122 E2 Determination of Unknowns from Qualitative Precipitations Name Check y

Question

CHM122 E2 Determination of Unknowns from Qualitative Precipitations Name Check your qualitative scheme below with your instructor if you are not sure you have a correct scheme. To determine which unknown is the positive ion unknown and which unknown is the negative ion unknown: Take two small test tubes from your drawer. To one add unknown A" and to the other add unknown "B" Add that unknown is the to both tubes. If a precipitate forms, then ion unknown. Whether or not a precipitate forms above, take two new small tubes from your drawer and add unknown "A" to one tube and unknown "B" to the other tube. Add that unknown is the to both tubes. If a precipitate forms, then on unknown My qualitative scheme for determining the positive ion unknowns is below: First add To remove Then add To remove Finally add To remove My qualitative scheme for determining the negative ion unknowns: First add To remove Then add To remove Finally ado To remove

Explanation / Answer

Qualitative scheme for anions is:

1. Take a vial and add silvernitrate solution to it. If white precipitate appears then it is chloride.centrifuge to remove the silver chloride precipitate completely.

2.Now, add few drops of concentrated nitric acid and then add Barium chloride solution to form white precipitate of barium sulphate.centrifuge it to remove the sulphate anion.

3. if the above two tests are not resulting in precipitates then introduce a litmus paper to identify the alkalinity due to the presence of OH-.

Qualitative tests for cations.

1. Take the vial and add dilute hydrochloric acid if it gives white precipitate then it means Ag+ is present.now add hotwater to the precipitate to dissolve it and add hot ammonium hydroxide to dissolve it.Then add dilute nitricacid solution to form thick white precipitate. Ag+ is confirmed.centrifuge it to remove the Ag+.

2.To the residue add ammoniumchloride and ammonium hydroxide followed by H2S if it gives black precipitate it will be Ni+2. wash the precipitate and add Aquaregia and dissolve it.Now add dimethyl glyoxime and ammonium hydroxide to form orange precipitate of nickel DMG.Centrifuge it to seperate the nickel ions.

3. to the residue now add ammonium hydroxide follwed by ammonium carbonate to get a white precipitate which shows the presence of barium ions.to the above precipitate add acetic acid and pottassium chromate to form yellow precipitate.which confirms the barium ion.

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