This is the protocol for a practical class I once took. The idea is that copper nitrate is converted to hydroxide, oxide, sulfate and then finally solid copper. I know that $\ce{CuO(s) + H2SO4(aq) -> CuSO4(aq) + H2O (l)}$, but can't you avoid converting the hydroxide to oxide altogether and just do $\ce{Cu(OH)2(s) + H2SO4(l) -> CuSO4(aq) + 2H2O(l)}$? Note that $\ce{NaCO3}$ is decanted and washed off before reacting copper (II) oxide with sulfuric acid, but surely you can also do the same thing with copper (II) hydroxide?

  • $\begingroup$ I'm not 100% sure, so I'm not posting this as an answer, but I believe it's because the Cu(OH)2 is quite dirty when it's produced. Cu(OH)2 really holds onto impurities well (here that would be sodium nitrate, carbonate, and hydroxide, largely), and the conversion to CuO cleans it up substantially. If you started with clean Cu(OH)2, I suspect that you would be able to convert it to the sulfate with sulfuric acid with little difficulty, but it has such a gloopy consistency that getting it cleaned up in hydroxide form is not an insignificant task. $\endgroup$ – Jason Patterson Jan 24 '16 at 3:03
  • $\begingroup$ Of course you could have avoided converting the hydroxide to oxide. Also, you could have avoided getting the hydroxide in the first place, and go from nitrate straight to sulfate. Oh wait, and what if we abandon all that and get your solid copper from nitrate in one step? See, it's a practical class, not a real-life technology problem. Its purpose is to get you familiar with certain procedures, and not to get from A to B as fast as one can. $\endgroup$ – Ivan Neretin Jan 24 '16 at 7:26
  • $\begingroup$ Hmm.. that's absolutely true. But considering the OP has already prepared the hydroxide , then conversion to oxide (and then sulphate) is the best way. $\endgroup$ – Varun Jan 24 '16 at 10:22
  • $\begingroup$ @IvanNeretin well I did ponder if we could get from copper nitrate to copper by just adding zinc like the prac says, but then we would get two solids forming which would be hard to separate. I'm not sure about going from nitrate to sulfate - I think it gives nitric acid instead of just water which may complicate the adding of zinc and removal of zinc by HCl. of course there may be an easier way with different chemicals/equipment but let's assume we don't have access to that. but yeah it's possible they're just adding steps, but I thought there could be a reason $\endgroup$ – k-- Jan 24 '16 at 21:32
  • $\begingroup$ Getting copper from copper nitrate is almost the same as getting copper from copper sulfate; if there is a problem of two solids (which is not that much of a problem, but whatever) in one of them, you'll encounter the same in the other one as well. Yes, they are just adding steps for the sake of teaching, though there are more-or-less real reasons too; these are nicely explained in the existing answers. $\endgroup$ – Ivan Neretin Jan 24 '16 at 22:10

I would like to add to what Jason has already mentioned:

1.Copper Hydroxide is comparatively tougher to handle since it contains a lot more impurities ( when we are converting Cu(II)nitrate to hydroxide using NaOH, the impurities could be sodium nitrate, excess sodium hydroxide. )

  1. Copper Hydroxide itself is blue, so the equivalence point (when exact amount of copper hydroxide has reacted with concentrated sulphuric acid) of the reaction would be hard to detect, and so yield would drop (since you would again have to neutralise the excess sulphuric acid before purification or conversion to copper metal).

  2. In contrast to this CuO is a black precipitate and can be easily isolated (comparatively) by a Hirsch funnel (or any such equivalent apparatus). This improves the overall yield of further steps and eases the process of purification.

Hope this helps.

  • $\begingroup$ Good points, and actually we don't even neutralise the H2SO4, we just decant it off and wash with water. first year labs for ya $\endgroup$ – k-- Jan 24 '16 at 21:31

1) Don't expect too much sense in practical chemistry classes, they often use ineffective, but tutoring approach

2) That said, copper hidroxide is very fluffy and adsorbs a lot of water. It is plainly a lot easier to wash compact copper oxide than fluffy copper hydroxide.

  • 2
    $\begingroup$ I disagree with your first point. It is always a good approach to understand minute details of a practical class, most of the procedures have been standardised with practice. They may not be the MOST effective , but certainly are made with the intent of being effective. If they are not effective,it is also helpful to find out why and improve over it. $\endgroup$ – Varun Jan 24 '16 at 10:19
  • $\begingroup$ @Varun , I once made phosporic acid from red phosphor in a practical class. Isn't it definition of impractical and ineffective ? $\endgroup$ – permeakra Jan 24 '16 at 10:33

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