If zinc is less reactive than sodium, then why does it still react with sodium hydroxide?
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3 Answers
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Indeed, $\ce{Zn}$ is lower than $\ce{Na}$ in activity series of metals, so the following reaction won't take place
$$\require{cancel}\ce{Zn + 2NaOH \cancel{→} Zn(OH)2 + 2Na}$$
Remember, however, that $\ce{Zn}$ is amphoteric, so it can reacts with a strong base such as $\ce{NaOH}$ as an acid forming sodium zincate
$$\ce{Zn + 2 H2O + 2 NaOH -> Na2Zn(OH)4 + H2}$$
P.S. I forget a lot of good ol' chemistry, and I have just realized that usually we do not call metals themselves amphoteric, but rather use this term for their oxides/hydroxides. For metals we just say that some of them (such as $\ce{Zn}$) dissolve both in acids and in bases. The point is that $\ce{Zn}$ does not react as an acid in the reaction above since the reaction is not an acid-base one, but rather oxidation-reduction. So, the answer then is that $\ce{Zn}$ reacts with aqueous solution of sodium hydroxide because it can be oxidized in these condition in accordance with the reaction mentioned.
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$\begingroup$ does this explain why? so zinc can react because it's amphoteric? $\endgroup$– NickCommented Sep 19, 2014 at 15:10
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12$\begingroup$ @Nick, chemistry (especially at school level) very rarely answers "why" questions. It is almost all about remembering answers to "what" questions, i.e. what happens when A and B are mixed together. What do you want me to do beyond that? Do you want me to calculate Gibbs energy for this reaction and show that it is negative so the reaction is favoured and then (somehow) estimate the reaction rate to show that it will indeed proceed in a reasonable amount of time? $\endgroup$– WildcatCommented Sep 19, 2014 at 15:57
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$\begingroup$ @Wildcat. The closest to real answers to why-questions you get is from computational chemistry using first-principles methods. Unfortunately we are not yet able to fully simulate chemistry in the bottle with this, and its doubtful that we ever will be. $\endgroup$ Commented Jun 10, 2017 at 19:14
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In effect zinc is not displacing sodium. It's displacing hydrogen. We expect a metal to do this from a hydroxide base if
- the metal is more reactive than hydrogen and
- the metal's own hydroxide can act as acid towards this base (amphoteric hydroxide).
Zinc passes both tests and so, party time!
answered Jun 10, 2017 at 14:04
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Zn is a amphoteric element. Therefore Zn can react with both acids and alkalis eliminating hydrogen. Learn more about amphoteric elements and compounds https://www.chemistryscl.com/chemistry_theories/amphoteric_compounds/main.php