Need help with coming up with a separation scheme Part 2: Designing and testing

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Need help with coming up with a separation scheme

Part 2: Designing and testing a separation scheme 2.1. Designing a separation scheme: Between Week 1 and Week 2 of lab, design a separation scheme for all 4 cations. Use the results of your preliminary tests and the reasoning illustrated in the introduction and the Pre-lab questions. Be sure to include equations for all the reactions which occur at each step in the scheme. Record the scheme in the data section of the lab notebook. The scheme MUST be submitted at the start of Week 2 laboratory period. It will be reviewed by the TA prior to the start of the lab period. Separation and Identification of Cations Student Na Lab Section Four lons which may be present: 3 Ions that are present: est t 21 Lab 5 (Metal Cations)- Page 9 of 20

Explanation / Answer

Add HCl and pass H2S gas through the solution containing the given ions

A black ppt will be formed of CuS. this can be separated by filteration

Cu+2 + S-2 ---> Cus( black ppt)

2) take small amount of solution containing the other three cations (already Cu+2 has been precipitated out). Add same amount of NaOH to it. Heat the mixture.

Both Ni+2 and Fe+3 will be ppt out

Ni2+(aq) + 2OH–(aq)Ni(OH)2(s)

Fe3+(aq) + 3OH–(aq)Fe(OH)3(s)

Filter the ppt out.

Dissolve the ppt in HNO3. Take small portion from it. Add ammonia solution to it. a precipitate will be formed. Separate the precipitate and keep the supertanant for further testing. to the ppt add HCl and 2-3 drops of NH4SCN.

A blood red colour confirms Fe+3.

Now to the supernatant above add Dimethyl Glyoxime. A red ppt cofirms Ni+2.

4) to the solution obtained after ppt of Fe+3 and Ni+2 add HNO3 followed by addition of ammonia solution[check for basic nature of solution]. A gel like ppt will be formed. Centrifuge out the ppt. Add HNO3 to the ppt stir till the ppt dissolves. Now add 4 drops of aluminon reagent and 10 drops of ammonia solution. A cherry coloured ppt will confirm Al+3.

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