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Redox reaction from dissolving zinc in copper sulfate

What happens when you add zinc to a solution of copper sulfate? Identifying the half reactions to see what got oxidized and reduced.  Created by Sal Khan.

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  • blobby green style avatar for user Erica Mitchell
    At , why is Copper more electronegative than Zinc?
    (7 votes)
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  • blobby green style avatar for user alexis97.JG
    at , why is SO4 negative 2? i thought it was positive?
    (2 votes)
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    • piceratops sapling style avatar for user Tristan
      SO4 is sulfate. It's one of the most common polyatomic anions, so this might be good to memorize.
      Oxygen and Sulfur both have 6 valence electrons. In order to be stable Oxygen needs to make 2 bonds, so Sulfur has to bond with all of them.
      See the issue yet? Sulfur can only make 6 bonds with 6 electrons, but 4 Oxygens would require it to make 8 bonds.
      Sulfur has a 'charge' of 6+ and the Oxygen has a 'charge' of 8-.
      In order for the molecule to be formed it has to take 2 electrons from some other atom/molecule. Doing so allows it to form SO4(2-)
      (12 votes)
  • blobby green style avatar for user Gaven Schlosser
    Did Zinc dissolve into the water because the loss of electrons caused instability in its metallic solid form?
    (4 votes)
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    • leaf red style avatar for user FTB
      Zinc reacted and lost its' valence electrons, thus forming ions, which are not water soluble. The zinc ion is charged positively and water is a polar solvent (has a negative and a positive side to it) and therefore will dissolve to form colourless ions in solution.
      (3 votes)
  • female robot grace style avatar for user Aayu Pandey
    So if zinc lost electrons, zinc is oxidised. Than means zinc is providing its electrons to copper, and copper is reducing because of that. So zinc is the reducing agent and copper is the oxidising agent, right?
    (2 votes)
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    • piceratops tree style avatar for user kushagra
      I guess you are confused..try this one out "OIL RIG" that means Oxidation is losing electrons and Reduction is gaining electrons, So here Zinc is losing electrons so it is getting oxidized and Copper is gaining electrons that means it is getting reduced.
      (0 votes)
  • leaf green style avatar for user Jess Carrion
    is SO4 (4 subscript) Sulfate? around
    (3 votes)
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  • duskpin ultimate style avatar for user Abid Ahmed Zidan
    Why doesn't cu2+ take 2 electrons from so4 2-.instead of taking from zn?
    (2 votes)
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    • leaf red style avatar for user Richard
      The sulfate is composed of sulfur and oxygen atoms which are much more electronegative than copper. Copper doesn't possess enough electronegativity to take electrons from such an electronegative anion. Copper does have more electronegativity than zinc which is why copper takes electrons from zinc instead. Hope that helps.
      (2 votes)
  • blobby green style avatar for user gerardo
    at why do you get a redox reaction?
    (2 votes)
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    • piceratops seedling style avatar for user Ravi Kawade
      If you look at the Half-Reactions, you'll see that Zinc is oxidized and Copper is reduced at the same time.

      A redox reaction is a reaction where an oxidation and a reduction both take place at the same time. Thus, the above equation is a redox reaction. :P

      Hope this helps!
      (1 vote)
  • leaf green style avatar for user qiaochu xiong
    Is the electronegativity of copper ion the same as that of copper atom?
    (2 votes)
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  • piceratops seed style avatar for user Jasmine LaTrese Thomas
    At , how did the zinc dissolve with the copper sulfate?, Is that what the graph is showing?
    (1 vote)
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    • spunky sam blue style avatar for user Sebastian Skwarczyński
      On the left graph is what was before the reaction: there is some copper sulfate dissolved while the zinc metal just can't dissolve. On the right graph is what is after the reaction: there is some zinc sulfate while this time the copper metal is the thing to stay in the solid form (not dissolved). Just remember that there is also lots of water on both sides that dissolves these sulfates, but doesn't appear in the equation since it does not take place in the main reaction. If this what i written doesn't make things clear, then comment my answer, if it does, you can vote for it (i don't require a vote, but this is my first answer and i would be happy for the first vote).
      (2 votes)
  • blobby green style avatar for user Cui Yi L
    What is the differences between redox reaction and displacement reaction?
    (1 vote)
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    • aqualine ultimate style avatar for user gaiki.amruta
      I think that a displacement reaction is always a redox reaction. But, a redox reaction is not always a displacement reaction.

      If you want the definition,

      A reaction in which oxidation and reduction takes place simultaneously is known as a redox reaction.

      A reaction in which a more reactive element displaces an element of lesser reactivity from its aqueous compound is known as a displacement reaction.

      Reactivity series:K>Sr>Ca >Na >Mg >Al >Zn >Cr >Fe >Cd >Co >Ni >Sn >Pb

      Hope this helps :)
      (2 votes)

Video transcript

So what we have here is a solution of a copper sulfate. And copper sulfate is an ionic compound. The copper loses two electrons to the sulfate. So the copper has a positive 2 charge, and the sulfate has a negative 2 charge. This is a cation. This is an anion. So you could imagine it's very easy to dissolve it in a polar solvent like water. So this is an aqueous solution. We are dissolving it in water, and it actually does have this blue color. So one way to think about it is this is a bunch of copper cations dissolved in water and a bunch of sulfate anions also dissolved in this water right over here. Now, we're going to do a little bit of an experiment. We're going to take some solid zinc, and solid zinc would have this kind of metallic gray color. We're going to take a powder of solid zinc metal, and throw it into this solution, and think about what is going to happen. So that's solid zinc right over there. So zinc in the solid state plus inside of this solution of copper sulfate, what do we think is going to happen? And I actually encourage you to pause the video, look at this table of electronegativities, and look at what's going on here. Think about who has the electrons and who might want the electrons, and then think about what you think is going to happen. Well, let's look at the electronegativities right over here. Copper is more electronegative than zinc is. And so, if there was a way for copper to take electrons from the zinc, it would, especially this copper right over here. These are positively charged coppers. They would love nothing more than to take some electrons and become neutral. And look-- there's someone to take those electrons from. And so what you get is a redox reaction. And we'll look at the half reactions in a second. You get a redox reaction where the copper takes electrons from the zinc. So it becomes neutral solid copper. And the zinc loses those electrons to the copper. And so those become zinc cations. Or you could think of it as zinc sulfate dissolved in the aqueous solution. So let me write that down. Zinc sulfate, and that has a negative charge still, and it is in an aqueous solution. So what will this actually look like? Let me put another glass here. So this is before the reaction starts. After the reaction, it's going to look something like this. Zinc sulfate is actually a clearish looking liquid. So let me draw that. The liquid will actually become clear. So zinc sulfate is a clearish liquid. And instead of having solid zinc here, now you're going to have solid copper that will have precipitated out of the solution. So that's pretty neat. And just to make sure that we understand it in terms of oxidation and reduction, let's think about the half reactions here. So let's think about the half reaction for zinc. So solid zinc right over here, it has a neutral oxidation state. It has no charge. And then we end up right over here with zinc that has a positive charge, a positive 2 charge. So what happened right here? It lost electrons. It got oxidized. So it lost two electrons. The zinc got oxidized. And then what happened to the copper? Well, the copper started as a cation. So it started in the aqueous solution. And then it gained two electrons. Each ion of copper gained two electrons. And then we end up with neutral copper in the solid state. So it's oxidation number was reduced. It became more negative. So we could say that the copper was reduced by the zinc, the zinc oxidized by the copper. And we see that the sulfate, its charge didn't change. And when you're dealing with an actual ionic compound, the oxidation state is its actual charge. It's not hypothetical anymore.