Hydrogen gas is produced when zinc reacts with hydrochloric acid. if the actual yeild of this reaction is 85%, how many grams of zinc are needed to produce 112L of H2 at STP?
The reaction is:
Zn + 2HCl --> ZnCl2 + H2
1 mole of any gas at STP is 22.4 L
112L of H2 / 22.4 L/mol = 5 moles H2
(5 mol H2)(1 mol Zn / 1 mol H2) = 5 moles of Zn
The above relationship assumes that the reaction is 100% efficient. Since the reaction is only 85% efficient, MORE than 5 moles of Zn must be used. I will let you figure that part out on your own. [The multiplier you use has to do with the relationship of 100% to 85%]
i don't get what to do next, can you please show me??
multiply the 5 moles of zinc by the factor:
(1.00/0.85)
then what do i do??
5 mols Zn x (100/85) = ?? mols Zn
You want grams, Convert mols Zn to grams by grams = mols x molar mass.
To calculate the amount of zinc needed to produce a certain volume of hydrogen gas at STP (standard temperature and pressure), we need to follow these steps:
Step 1: Determine the balanced chemical equation for the reaction.
The balanced chemical equation for the reaction between zinc (Zn) and hydrochloric acid (HCl) is as follows:
Zn + 2HCl -> ZnCl2 + H2
Step 2: Convert the given volume of hydrogen gas (112L) to moles using the ideal gas law.
The ideal gas law states: PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin. At STP, the pressure (P) is 1 atm and the temperature (T) is 273 K.
Thus, n = (PV) / RT.
Given:
V (volume of hydrogen gas) = 112L
P (pressure) = 1 atm
R (ideal gas constant) = 0.0821 L.atm/mol.K
T (temperature) = 273 K
Substituting the values into the formula:
n = (1 atm * 112L) / (0.0821 L.atm/mol.K * 273 K)
n = 4.071 moles of H2
Step 3: Use the stoichiometry of the balanced equation to determine the amount of zinc needed.
From the balanced equation, we can see that 1 mole of Zn reacts to produce 1 mole of H2. Therefore, the number of moles of Zn needed is also 4.071.
Step 4: Convert the moles of zinc to grams using its molar mass.
The molar mass of zinc (Zn) is 65.38 g/mol.
Using the formula:
mass = moles * molar mass
mass = 4.071 moles * 65.38 g/mol
mass = 266.331 g
So, approximately 266 grams of zinc would be needed to produce 112L of hydrogen gas at STP with an actual yield of 85%.