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Based on an experiment, a solution that contained $\ce{Cu^2+}$ formed a precipitate with $\ce{NaOH}$. Is this how you write the equation?

$$\ce{2NaOH + Cu^{2+} -> Cu(OH)2 + 2Na+}$$

On the experiment: solution A is mixed with NaOH (solution turned white). Using a flame test solution A is color green. I figured solution A has $\ce{Cu^{2+}}$ ion.

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  • $\begingroup$ Looks good to me. $\endgroup$ – Zhe Dec 19 '16 at 1:45
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Yes, the reaction is correct however it may be preferable to either include all or no spectator ions. Use either a net ionic equations (omit the Na+), molecular equation (include the copper compound full) or complete ionic equation.

For example, if the compound is copper sulphate the equations would be (without states)

Net ionic $$\ce{Cu^2+}+\ce{2OH^-->Cu(OH)_2}$$ Molecular equation $$\ce{CuSO_4}+\ce{2NaOH->Cu(OH)_2}+\ce{Na_2SO_4}$$ Complete Ionic Equation $$\ce{Cu^2+ +SO_4^{2-}}+\ce{2Na^+ +2OH^-->Cu(OH)_2}+\ce{2Na^+ +SO_4^2-}$$

Edit

In the case where you don't know what copper compound it is, use a net ionic equation. As a side note, copper hydroxide is not white. You might want to check your calculations.

If you're wondering what it is, check what other compounds will emit green.

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  • $\begingroup$ Usually a ppt is indicated in a chemical reaction as: $$\ce{Cu(OH)2 v}$$ or $$\ce{Cu(OH)2_{(s)}}$$ Also dissolved ionic species can be indicated so: $$\ce{Na2SO4_{(aq)}}$$. $\endgroup$ – MaxW Dec 19 '16 at 19:16

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