In this lab we used a redox reaction and precipitation reactions in order to find the composition of pennies. A redox reaction is a reaction where the reducing agent transfers electrons to the oxidizing agent. In this reaction the charge of the atom being reduced goes down because of it gaining electrons and the charge of the atom being oxidized goes up because of the loss of electrons. A precipitation reaction is a reaction that sometimes forms an insoluble compound when a solution that contains a particular cation reacts with a solution that contains a particular anion. What we expected to do in the lab was be able to find the percent of the Zn in the penny using titration and stoichiometry.
Throughout the duration of the lab these are the materials that were used: HCl solution
post 1982 penny
The first step of this experiment was to place one penny in 50mL of HCl. The HCl ate the Zn in the penny overnight. SO what was left was the copper shell only leaving the Zinc Chloride solution. Which ment that excess the HCl that was discussed in the pre-lab is in the solution as well. Next was to tirate NaOH with excess HCl in the solution using a Phendeptholein indicator. When using 10mL of the ZnCl2 solution we got Zn(OH)2. Next we transferred the solution to the Erlenmeyer flask with drainer and filter paper by using a vacuum to pull liquid through the paper. Once that was done we dried the Zn(OH)2, weighed it and recorded the data. Once all the data had been recorded, we used Stoichiometry to find the percent of Zn in the penny. Amount of Cu
Amount of Zn
% of Cu
Percent of Zn
By using the chemical equations and stoichiometry, we were able to find the amount of grams in the Zn and Cu and then the percent of each. The result we got were spot on with the accepted values. So there was a 0% error! I understand that the experiment had to be done over a couple times due to over titration but once we did it the correct way we received quite favorable results which shows in the 0% error we calculated. So yes out data does concede with the theory and we were successfully able to calculate the percent of Zn. In conclusion, from this experiment I received more practice on using stoichiometry and the ability to titrate correctly. The stoichiometry was not only used to find the amount in grams but we also got some practice finding percent’s of elements in different compounds. Overall our experiment was successful and produced favorable results.