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Qualitative Analysis 2 Known/Unknown Cheat Sheet by

Lab Prep

Clean beakers and test tubes (make sure small test tubes).
Grab strips of different colored washi tape for labeling.
Grab disposable pipettes.
Fill soap and distilled water.

Separation of Quall II ions:

Separation of Qual II ions done with strong base, NaOH.
Mn 2+, Ni2+, Fe2+. Will precip­itate as a Hydrox­ides.
Al3+ and Zn2+ will precip­itate soluble Hydrox­ides.
Add 2 mL of original solution to small cleaned test tube. (DO NOT USE 2 mL WHEN DOING UNKNOWN)
Add 15 drop of 6M NaOH
Centrifuge and save precip­itate and supernate. (Test for incomplete reaction; several drops of 6 M NaOH)
Label supernate "Al & Zn ions".
Dissolve the precip­itate with the minimum amount of concen­trated Nitric Acid (HNO3) possible.
If necessary heat the solution.
Label dissolved, " Mn, Ni, & Fe ions"

Testing for Mn 2+ Presence

Add approx­imatly 1/2 of "Mn, Ni, & Fe" to a small test tube. (DO NOT USE THAT MUCH IF DOING QUAL II UNKNOW­N."
Add solid NaBiO3 in excess to the solution and centri­fuge.
Deep purple solution confirms Mn 2+ ion presence.

Testing for the presence of Fe 3+

Add remaining 1/2 solution of "Mn, Ni, & Fe" (DO NOT USE ALL IF DOING QUAL II UNKNOW­N"
Excess ammonia does not react with Mn the addition is to make Fe a brown precip­itate and Ni a blue supernate.
Add 5 drops of $M NH4Cl to the solution
Add concen­trated ammonium hydroxide (NH4OH) till it is basic to litmus.
Add additional three drops to check for reaction comple­tion.
Centerfuge & save supernate label for Ni testing
Dissolve percip­itate with 6M HCl
Add 5 drops of 0.1M NH4SCN. Presence of blood red color confirms presence of Fe.

Testing for Ni Presence

Complexing agent (Dimet­hyl­gly­oxime) reacting specif­ically with Ni ions
Using test tube labeled Ni supernate
Appearance of pinkish red precip­itate.

Testing for Al Presence

Addition of acid breaks down Al & Zn Hydroxides to ions
Add HNO3 drop wise to supernated labeled "Zn & Al ions" solution must be basic to litmus paper.
Add 5 more drops after that to insure reaction comple­tion.
Presence of white cloudy percip­itate indicated presence of Al ions.`
Centerfuge and save Zn supernate for analysis.

Testing for Zn percip­itate

Addition of 6M HCl to supernate Zn+ until solution is acidic to litmus paper
Add 3 drop of 0.2M K4[Fe(­CN)6] and stir.
Centrifuge and discard supernate.
Light green precip­itate confirms presence of Zn.
 

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  • Published: 29th March, 2017

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