[PbZeppelin]

Hey guys, my finals are coming up in a few days.

Why do we need to put the crude CuI product in ethanol, then centrifuge it, decant and repeat it with diethyl ether? Why does ethanol have to be used BEFORE diethyl ether? Does it have to do with the different polarities of the solvents? Also, why is it recommended that we centrifuge twice for each solvent (ie: shake hard to disperse solids after the first round before putting it back into the centrifuge)?

Any help would be greatly appreciated. Thanks!

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Hi guys, I'm new here and my finals are coming soon.

For the purification of Copper(I) Iodide, why do we wash it with water, then ethanol, then diethyl ether in between rounds of centrifugation? What's the significance of this sequence? Why does it have to be centrifugated with the most polar solvent first and the least polar solvent last?

Any help would be greatly appreciated. Thanks!

[Babcock_Hall]

Please provide your thoughts first.  According to the Forum Rules (see red link above), only then can we help you.

[PbZeppelin]

Ok. My guess is that we have to use a more polar solvent first for the polar impurities to interact more strongly with when the tube is shaked.  After centrifugation, the impurities (and a little bit of CuI) remain in solution and get decanted while the remaining CuI product is collected in one lump. A less polar solvent is then used to remove the smaller amount of impurities left without further compromising the amount of CuI (which is a polar ionic compound).
Did that make sense? I'm hoping to get to the bottom of this.
Thanks!

[Babcock_Hall]

Are water and diethyl ether miscible or immiscible?

[PbZeppelin]

Immiscible, because water is polar but diethyl ether is non-polar.

[Babcock_Hall]

I will proceed under the assumption that removing some water is one goal of these steps.  Is ethanol miscible in water?  Is it miscible in diethyl ether? 

[PbZeppelin]

Ethanol is somewhat miscible in diethyl ether but not really in water. I guess the addition of ethanol somehow displaced water? The addition of diethyl ether after ethanol probably makes it easier for the solid to dry because diethyl ether is more volatile. That's my guess.

Is purifying the product even one of the aims here?

[PbZeppelin]

Oops, I meant that ethanol is also soluble in water because it can form hydrogen bonds with water. So I guess adding ethanol will allow the solid to dry more easily

[Babcock_Hall]

I think that ethanol may remove most of the water, and diethyl ether will help remove the ethanol.  Do you think that the water may remove some impurities?