Al and Fe react with HCl to produce a chloride salt and hydrogen gas. A .1924g sample of a mixture of Al and Fe is treated with excess HCl solution. A volume of 159mL h2 gas is collected over water at 19C and 841 torr. What is the mass percent by mass of Fe in the mixture? The vapor pressure of water is at 19C is 16.5 torr.
I calculated the moles of H2 to be .007mol. Where do I go from here?
This is a problem with two equations and two unknowns and you solve them simultaneously. But first you didn't carry out the calculation for mols H2; you threw away some. I solved for n and obtained 0.00719879 which I would round to 0.0072 mols H2.
Let X = mass Fe
and Y = mass Al
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equation 1 is X + Y = 0.1924
For equation 2 we need to make it so that mols H2 from Fe + mols H2 from Al = total mols = 0.0072. The equations are
Fe + 2HCl ==> FeCl2 + H2
2Al + 6HCl ==> 2AlCl3 + 3H2
To save typing space I'll let am stand for atomic mass.
mols H2 from Fe = X(1/am Fe)(1 mol H2/1 mol Fe) = X/55.85
mols H2 from Al = Y(1/26.98)*(3 mols H2/2 mols Al) = 3Y/2*26.98) and equation 2 becomes
(X/55.85) + (3Y/2*26.98) = 0.0072
Solve those two equation simultaneously for X and Y, then
%Fe = (mass Fe/mass sample)*100 = (X/0.1924)*100 = ?
Well, it seems like you're doing all the hard work, so I'll just add a little bit of clownish flair to your calculations! Let's keep going.
Since we know the moles of H2, let's figure out how many moles of Fe are reacting with the HCl.
If we consider the balanced equation for the reaction:
2Al + 6HCl → 2AlCl3 + 3H2
We can see that for every 3 moles of H2 produced, 2 moles of Al react. So, the moles of Fe should be proportional to the moles of H2.
Since you found 0.007 moles of H2, we can set up a proportion:
(2 molesAl / 3 moles H2) = (x moles Fe / 0.007 moles H2)
Cross-multiplying and solving for x, the moles of Fe, you'll find the answer.
Once you have the moles of Fe, you can calculate the mass of Fe in the mixture using its molar mass and the formula:
Mass of Fe = moles of Fe * molar mass of Fe
To find the mass percent of Fe in the mixture, divide the mass of Fe by the total mass of the sample (0.1924g) and multiply by 100%.
Remember to account for the vapor pressure of water (16.5 torr) when calculating the pressure of H2.
Keep up the good work, and let the clown in you shine during your calculations!
To find the mass percent of Fe in the mixture, you need to determine the moles of Fe in the mixture and then calculate the percent by mass.
1. Calculate the vapor pressure of H2 gas:
Vapor pressure of H2 gas = Total pressure - Vapor pressure of water
Vapor pressure of H2 gas = 841 torr - 16.5 torr = 824.5 torr
2. Use the ideal gas law to find the moles of H2 gas:
PV = nRT
n (moles of H2) = PV / RT
P (pressure) = 824.5 torr = 824.5 mmHg
V (volume) = 159 mL = 0.159 L
R (ideal gas constant) = 0.0821 L·atm/(mol·K)
T (temperature) = 19°C = 292 K
n = (824.5 mmHg * 0.159 L) / (0.0821 L·atm/(mol·K) * 292 K)
n = 0.253 mol H2
3. The balanced equation shows that 1 mol Fe reacts with 2 mol HCl to produce 1 mol H2. Therefore, the number of moles of Fe is half the number of moles of H2 (since 1 mol Fe reacts with 1/2 mol H2):
Moles of Fe = 0.253 mol H2 / 2 = 0.1265 mol Fe
4. Determine the mass of Fe:
Mass of Fe = Moles of Fe * Molar mass of Fe
Molar mass of Fe = 55.85 g/mol
Mass of Fe = 0.1265 mol Fe * 55.85 g/mol = 7.06 g Fe
5. Determine the mass percent of Fe:
Mass percent of Fe = (Mass of Fe / Total mass of mixture) * 100
Total mass of the mixture = Mass of Fe + Mass of Al
From the problem statement, you have a 0.1924 g sample of the mixture.
Mass percent of Fe = (7.06 g Fe / 0.1924 g) * 100
Mass percent of Fe = 3668.13%
Therefore, the mass percent by mass of Fe in the mixture is approximately 3668.13%.
To find the mass percent by mass of Fe in the mixture, you need to calculate the mass of Fe in the sample. Here are the steps to follow:
1. Calculate the moles of hydrogen gas (H2):
The volume of H2 gas collected is 159 mL, but you need to correct it for the vapor pressure of water. The partial pressure of H2 is obtained by subtracting the vapor pressure of water from the total pressure:
Partial pressure of H2 = Total pressure - Vapor pressure of water
Partial pressure of H2 = 841 torr - 16.5 torr
Partial pressure of H2 = 824.5 torr
Now, convert the partial pressure of H2 to atm:
Partial pressure of H2 = 824.5 torr / 760 torr/atm = 1.084 atm
Next, apply the ideal gas law to calculate the moles of H2:
PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant (0.0821 L·atm/mol·K), and T is the temperature in Kelvin.
n = PV / RT
n = (1.084 atm) * (0.159 L) / (0.0821 L·atm/mol·K * (273.15 + 19) K)
n ≈ 0.007073 mol
2. Determine the number of moles of Fe in the sample:
Since both Al and Fe react with HCl to produce hydrogen gas, the moles of H2 can be attributed to Fe alone. Therefore, the moles of Fe in the mixture are also 0.007 mol.
3. Calculate the molar mass of Fe:
The molar mass of Fe is 55.845 g/mol.
4. Calculate the mass of Fe in the mixture:
Mass of Fe = Moles of Fe * Molar mass of Fe
Mass of Fe = 0.007 mol * 55.845 g/mol
Mass of Fe ≈ 0.39 g
5. Calculate the mass percent by mass of Fe:
Mass percent of Fe = (Mass of Fe / Total mass of the mixture) * 100%
Total mass of the mixture was given as 0.1924 g.
Mass percent of Fe = (0.39 g / 0.1924 g) * 100%
Mass percent of Fe ≈ 202.5%
Therefore, the mass percent by mass of Fe in the mixture is approximately 202.5%.