# Pre- Lab Theoretical Calculations Pre- Lab “Theoretical” Calculations

Mass of Penny:

If a penny made after 1982 is theoretically 97.5% zinc and 2.5% copper, using your penny’s mass indentify the following theoretical values:

Theoretical Mass of Cu =

Theoretical Mass of Zn =

Write the reactions that take place when the penny is place in the HCl acid bath, including “NR” or no reactions that take place:

Using the information above predict the following “theoretical” values

1) How many moles of copper are present?

2) How many moles of zinc are present?

3) How many copper atoms are present?

4) How many zinc atoms are present?

5) Assuming sufficient HCl, calculate how many Liters of Hydrogen are produced using zinc’s mass reacting in the HCl?

6) How many mL of Hydrogen are produced assuming sufficient HCl?

------Challenge Problems------

7) If the density of the HCl solution is 1.09 g/mL, and you are using a volume of 30.0mL of acid, what is the mass of the acid?

8) If you know the mass of the HCl acid and the mass of zinc, perform a limiting reactant problem and see how much hydrogen gas is produced, but before you do make a hypothesis as to which reactant will “limit” the reaction, and EXPLAIN how you came up with this hypothesis, then confirm or refute your hypothesis.

Post- Lab “Actual”Calculations:

Identify the following actual values:

Mass of Cu =

Mass of Zn =

Write the reactions that take place when the penny is place in the acid bath, including “NR” or no reactions that take place:

Using the information above predict the following “actual” values

1) How many moles of zinc are actually present?

2) How many Liters of Hydrogen are actually produced, if your zinc mass measured is ______g and the mass of HCl is ______g ? (limiting reactant style problem)

3) How many mL of Hydrogen are produced?

4) Identify the limiting reactant, is question #2 does this agree with you hypothesis? EXPLAIN how you know this is the limiting reactant

Now calculate the percentage yield of the liters of hydrogen produced by taking the actual yield you got during the lab divided by the theoretical yield you were supposed to get

Identify errors and hypothesize possible mistakes that were made, and explain how stoichiometry is used, and why it is so useful for a chemist to have strong knowledge of stoichiometry