The purpose of this lab is to determine the percent mass of Cu in a penny and see if the fabricator that makes the planchets for the government is using the correct amounts of Cu in the pennies. The composition of a standard penny is 97.5% Zn and 2.5% Cu. In the lab we will be using Beer’s Law (A=elc+b where A is solution absorbance, e is a constant called molar absorbency, l is the length in cm, and c is the concentration). Using Beer’s Law in this lab a colorimeter is used to find the absorbance and from this the concentration of dissolved Cu2+ ions can be found and percent mass calculated. The techniques used in this lab are useful in that they provide little human error for various parts of the lab by taking the measurements by a colorimeter human error is reduced.
M1V1=M2V2, Beers Law: A=elc+b, Morality= M = (mols of solute)/ (Liters of Solution)
Reaction: 3Cu(s) + 8 H3O+ (aq) + 2NO3- (aq) 3Cu2+(aq) + 2NO (g) + 12 H2O (l) Cu(s) + 4 …show more content…
At first the solution bubbled and then an orange-brown gas was released and the final solution was Blue – Green. In table one the concentration transmittance and absorbance are show witch give the point to the calibration curve used below. The 0.9993 Correlation demonstrates how the relationship between concentration and absorbance are directly related as one increases so does the other. The % mass of Cu in an actual post-1982 penny is 2.5% mass. This shows that the class discovered higher percent mass calculation than actually in the penny yet the data is close enough to verify that the % mass of Cu in the pennies is 2.5%. The percent errors for this lab as a whole varied significantly which shows that the procedures in the lab could have problems. This may be caused by the significant reliance on human