472 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
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.
472 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.
I 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.
the molar mass of aluminum will be on your periodic table.
Let's go through each part of the question to check your answers and help you understand the process:
B. What is the water vapor pressure at 26 degrees C? Using the chart provided I have 25.2.
It seems like you are using a provided chart to determine the water vapor pressure at 26 degrees Celsius. According to the information provided, the vapor pressure for water at 26 degrees Celsius is 25.2 mm Hg. Great job!
C. What is the partial pressure (in atmospheres) of dry hydrogen gas in the mixture?
To determine the partial pressure of the dry hydrogen gas, you need to subtract the water vapor pressure from the total atmospheric pressure. So, the partial pressure of the dry hydrogen gas can be calculated as follows:
Partial pressure of dry hydrogen gas = Total atmospheric pressure - Water vapor pressure
Partial pressure of dry hydrogen gas = 754 mm Hg - 25.2 mm Hg
Partial pressure of dry hydrogen gas = 728.8 mm Hg
Remember to convert mm Hg to atm:
Partial pressure of dry hydrogen gas = 728.8 mm Hg * (1 atm / 760 mm Hg) = 0.95842105 atm
Rounded to three decimal places, the partial pressure of dry hydrogen gas is approximately 0.958 atm. Therefore, your calculation is correct.
D. Calculate the number of moles of H2 produced by this reaction using the ideal gas law.
To calculate the number of moles of H2 gas, we can use the ideal gas law equation:
PV = nRT
Where:
P = pressure in atm
V = volume in L
n = number of moles
R = ideal gas constant (0.0821 L·atm/(mol·K))
T = temperature in Kelvin
First, we need to convert the volume of hydrogen gas to liters, as the ideal gas law requires the volume in liters. Since 472 mL is equal to 0.472 L, we can proceed with the calculation:
n = (P * V) / (R * T)
n = (0.958 atm * 0.472 L) / (0.0821 L·atm/(mol·K) * (26 + 273.15) K)
n = 0.0183458473 mol
Therefore, the number of moles of H2 gas produced by the reaction is approximately 0.0184 mol. Your calculation is correct.
E. Use the data from the experiment to calculate the experimental molar mass of zinc in g/mol.
To calculate the experimental molar mass of zinc, we need to use the number of moles of zinc produced and the mass of zinc reacted:
Experimental molar mass of zinc = mass of zinc / number of moles of zinc
mass of zinc = mass of H2O + mass of Zn
mass of Zn = mass of H2O + mass of ZnCl2 + mass of H2
From the given information, we know that the mass of zinc reacted is 1.256 g.
mass of zinc = 1.256 g
Experimental molar mass of zinc = 1.256 g / 0.0184 mol
Experimental molar mass of zinc = 68.478 g/mol
Therefore, the experimental molar mass of zinc is approximately 68.478 g/mol. It seems you made an error in the calculation. Please check your calculations again.
F. What is the molar mass of zinc from the periodic table (known value)? 65.39 g/mol
The molar mass of zinc from the periodic table is given as 65.39 g/mol. This is a known value that you should compare your experimental molar mass with.
G. Calculate the percent error for the experimental molar mass of zinc.
The percent error can be calculated using the formula:
Percent error = ((experimental value - known value) / known value) * 100
Using the values obtained:
Percent error = ((68.478 g/mol - 65.39 g/mol) / 65.39 g/mol) * 100
Percent error = 4.723%
Therefore, the percent error for the experimental molar mass of zinc is approximately 4.723%. It appears that you made an error in your calculation.