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July 28, 2016
Posted by **Jeremiah** on Monday, November 19, 2012 at 6:29pm.

A. Write the balanced chemical equation (I have this)

Zn + HCl ---> ZnCl2 + H2

B. What is the water vapor pressure at 26 degrees C? Using the chart provided I have 25.2

C. What is the partial pressure (in atmospheres) of dry hydrogen gas in the mixture?

Not sure if I have this correct, but I came up with: 0.959 atm

D. Calculate the number of moles of H2 produced by this reaction using the ideal gas law.

I have 0.0184 mol H2

E. Use the data from the experiment to calculate the experimental molar mass of zinc in g/mol.

I think I have this part correct. 0.0192 g/mol

F. What is the molar mass of zinc from the periodic table (known value) 65.39 g/mol

G Calculate the percent error for the experimental molar mass of zinc.

I am confused here. Using the values I have above I am coming up with 99.97%.

Can anybody help me and tell me if I am doing this correctly? My class is behind so my chemistry lecture class is not on track with my chemistry lab and I have two different professors. So I am having to do this homework and we haven't even gone over this stuff yet.

- chemistry -
**DrBob222**, Monday, November 19, 2012 at 10:51pm472 mL of H2 gas was collected over water when 1.256 g of Zn reacted with excess HCl. The atmospheric pressure during the experiment was 754 mm Hg and the temperature was 26 degrees C.

A. Write the balanced chemical equation (I have this)

Zn + HCl ---> ZnCl2 + H2

B. What is the water vapor pressure at 26 degrees C? Using the chart provided I have 25.2

C. What is the partial pressure (in atmospheres) of dry hydrogen gas in the mixture?

Not sure if I have this correct, but I came up with: 0.959 atm**That's right.**

D. Calculate the number of moles of H2 produced by this reaction using the ideal gas law.

I have 0.0184 mol H2**I have (0.959x0.427)/(0.08206*299)] = n = 0.01669 which you can round.**

E. Use the data from the experiment to calculate the experimental molar mass of zinc in g/mol.

I think I have this part correct. 0.0192 g/mol**mol = g/molar mass; rearrange to molar mass = (g/mol) = 1.256/0.01669 = 75.26 g/mol**

F. What is the molar mass of zinc from the periodic table (known value) 65.39 g/mol

G Calculate the percent error for the experimental molar mass of zinc.

I am confused here. Using the values I have above I am coming up with 99.97%.**% error = [(exp value-actual value)/(actual value)]*100 =**

[(75.26-65.38)/65.38]*100 = about 15% but that's just a close number. - chemistry -
**Jeremiah**, Wednesday, November 21, 2012 at 10:02amI went to our school's tutoring lab and received the explanation I needed to understand this. However I have another related question. I don't know if you will see this or not. Suppose we have a similar problem, except using Aluminum and HCl. The ratio is different. I am lost on part E again. In the above problem I understand why you can figure out the molar mass of zinc because 1 mole zinc is consumed for every 1 mole H2 produced. In the equation 2Al + 6HCl ---> 2AlCl3 + 3H2 for every 2 Al consumed 3 moles of H2 is produced. I am having a problem understanding how you would find the molar mass of Aluminum.

- chemistry -
**kira**, Monday, April 14, 2014 at 11:39amthe molar mass of aluminum will be on your periodic table.