Silver Copper Replacement Lab? Wait...what?

Fact: Copper wire reacts with aqueous silver nitrate.
 Fact: We did a lab about this 5 weeks ago.
 Fact: I should not slack on my blog posts.


 So obviously we did another lab, the purpose of this one was to demonstrate a replacement reaction, and show us mole ratios in action, in our case we were taking silver nitrate and copper, trading out the silver for copper, and creating copper nitrate and pure silver. We did this by suspending a copper wire in an aqueous solution of silver nitrate and letting it sit for a day, and then observing the reaction. To make the aqueous solution we mixed silver nitrate (AgNO3) with distilled water until it had dissolved. We then placed a coil of copper wire in the solution, covered the tube with wax, and let it sit in the fume hood until day two. During the time we were waiting for the reaction to take place we sat down and did some math. Using the equation 2AgNO3 + Cu ----> Cu(NO3)2 + 2Ag and we formed predictions for how much silver should be formed and how much copper became Cu(NO3)2 in the reaction.  I won't bore you with the details but, our predictions said that we should expect to form about .4513g (.0071 mol) of Ag and loose about .2269g (.0036 mol) of Cu in the reaction otherwise known as a 1:2 ratio of replacement. To explain how the experiment works in a more descriptive manner I will refer to one of my lab partners description:  <In the experiment, copper changed from its elemental form, Cu, to its blue aqueous ion form, Cu2+(aq). At the same time, silver ions (Ag+(aq)) were removed from solution and deposited on the wire in the elemental Ag metallic form.> On day two we observed that a crystal structure had formed on the copper wire in the tube (fig. 1). Sadly, we had to remove the structure to measure our results. We then emptied the test tube, and filtered the silver particles out of the copper nitrate solution, set the particles and the wire in the fume hood to dry overnight, and disposed of the copper nitrate solution. We are able to tell how much copper was used by measuring the new mass of the wire and comparing it to the mass from before the experiment. On day three we weighed the copper coil and silver nitrate, and then got to work figuring out how much Ag was formed and how much Cu was lost. In other words, more math...

(fig.1)

   

     Our predictions said that we should expect to form about .7703g of Ag and loose about .2269g of copper. The first step was changing the predictions we had from grams to mols, when we did this we got .0103 mol.of Ag, and .0036 mol of copper. In other words a 1 to 3 ratio of Cu to Ag. When this information was compared to our predictions (which said we would have a 1 to 2 ratio of Cu to Ag) we got 144% yield of silver and a 100% yield of copper. The inconstancy most likely stems from the paper we weighed our Ag on was still slightly wet and added weight to our readings. All in all, this was a pretty fun lab.