A 0.052g sample of aluminium reacts with excess 6M HCL. A 48.3mL volume of hydrogen gas was collected over water at 22C and the pressure of the hydrogen gas was 751mmHg.calculate the aluminum percent purity in the sample.
What volume of hydrogen gas at STP is produced from the reaction of 0.044g of 98.0% pure aluminium with excess 6M HCl.
A.
2Al + 6HCl ==> 2AlCl3 + 3H2
Look up vapor pressure H2O @ 22 C = and I've estimated 22 mm
Use PV = nRT to solve for mols H2 evolved.
For P you have
Ptotal = pH2 + pH2O
751 mm = pH2 + 22
Therefore, estimated pH2 = 751-22 = approx 729. Use that for P in the PV = nRT formula.
Remember T must be in kelvin; solve for n.
Using the coefficients in the balanced equation, convert mols H2 to mols Al.
Then g Al = mols Al x atomic mass Al.
%Al = (grams Al from calcn/0.052)*100 = ?%
B.
This is just the reverse process from part A above. This should get you started.
mass Al = 0.044 x 0.98 = ?
Convert to mols H2 from the equation.
Convert mols H2 to volume remembering that 1 mol at STP occupies 22.4 L.
To calculate the percent purity of aluminum in the first sample, you need to determine the amount of aluminum that reacted, and then compare it to the hypothetical amount that would react if all the aluminum in the sample were pure.
Here's how you can calculate the percent purity of aluminum in the first sample:
1. Determine the moles of hydrogen gas produced:
- Use the ideal gas law to convert the pressure of hydrogen gas to moles:
PV = nRT
n = PV / RT, where P is the pressure (751 mmHg converted to atm), V is the volume (converted to liters), R is the ideal gas constant (0.0821 L.atm/K.mol), and T is the temperature in Kelvin (22°C converted to Kelvin).
- Calculate the moles of hydrogen gas using the above formula.
2. Determine the moles of aluminum in the sample:
- Convert the mass of aluminum to moles by dividing it by the molar mass of aluminum (27 g/mol).
3. Calculate the percent purity:
- Divide the moles of aluminum in the sample by the moles of aluminum that would react if the sample were pure, and multiply by 100.
- Note: The stoichiometry of the reaction between aluminum and hydrochloric acid is 2 moles of aluminum for every 3 moles of hydrogen gas.
To calculate the volume of hydrogen gas at STP produced from the second sample, you need to use the stoichiometry of the reaction and the ideal gas law.
Here's how you can calculate the volume of hydrogen gas at STP produced from the second sample:
1. Determine the moles of aluminum:
- Convert the mass of aluminum to moles by dividing it by the molar mass of aluminum (27 g/mol).
- Multiply the moles of aluminum by the percent purity (98.0% purity) to account for impurities.
2. Determine the moles of hydrogen gas produced using stoichiometry:
- Use the balanced equation to determine the stoichiometric ratio between aluminum and hydrogen gas.
- For every 2 moles of aluminum, 3 moles of hydrogen gas are produced.
- Calculate the moles of hydrogen gas produced by multiplying the moles of aluminum by the stoichiometric ratio.
3. Convert the moles of hydrogen gas to volume at STP:
- Use the ideal gas law to convert moles of gas to volume:
PV = nRT
V = (nRT) / P, where n is the moles of gas, R is the ideal gas constant (0.0821 L.atm/K.mol), T is the temperature in Kelvin (0°C or 273 Kelvin), and P is the pressure at STP (1 atm).
- Calculate the volume of hydrogen gas using the above formula.
I hope this helps! Let me know if you have any further questions.