Write the overall reaction equation for the synthesis of aluminum potassium sulphate dodecahydrate, then determine the theoretical yield.
2Al+2KOH+4H2SO4+22H2O --> 2KAl(SO4)2*12H20
I don't know how to calculate theoretical yield from this. Please help?
Just the same as for any stoichiometry problem. Here is an example. The answer you get is the theoretical yield.
http://www.jiskha.com/science/chemistry/stoichiometry.html
To calculate the theoretical yield for the synthesis of aluminum potassium sulphate dodecahydrate, you need the balanced equation and the stoichiometry of the reaction. From the balanced equation, you can determine the molar ratio between the reactants and products.
The balanced equation for the reaction is:
2Al + 2KOH + 4H2SO4 + 22H2O → 2KAl(SO4)2·12H2O
This equation shows that for every 2 moles of aluminum (Al) used, 2 moles of potassium hydroxide (KOH), 4 moles of sulfuric acid (H2SO4) and 22 moles of water (H2O) are also consumed. The reaction yields 2 moles of aluminum potassium sulphate dodecahydrate (KAl(SO4)2·12H2O).
To calculate the theoretical yield, you need the mass of the limiting reactant, which is the reactant that is completely consumed first and limits the amount of product that can be formed. In this case, you need to identify the reactant that is present in the smallest quantity compared to its stoichiometric coefficient.
Once you have identified the limiting reactant, you can calculate the number of moles of the limiting reactant used based on its mass. Then, using the mole ratio from the balanced equation, you can determine the corresponding number of moles of the product. Finally, you can convert the moles of the product to grams using its molar mass.
For example, let's say you have 4 grams of aluminum (Al) and 6 grams of sulfuric acid (H2SO4). To determine the limiting reactant, you need to convert the masses of the reactants to moles. The molar masses, calculated from the atomic masses, are 26.98 g/mol for aluminum and 98.09 g/mol for sulfuric acid.
Moles of Al = mass of Al / molar mass of Al = 4 g / 26.98 g/mol ≈ 0.148 mol
Moles of H2SO4 = mass of H2SO4 / molar mass of H2SO4 = 6 g / 98.09 g/mol ≈ 0.061 mol
Based on the balanced equation, the mole ratio between aluminum and sulfuric acid is 2:4. This means that 2 moles of aluminum react with 4 moles of sulfuric acid to produce 2 moles of aluminum potassium sulphate dodecahydrate.
Since the ratio of aluminum to sulfuric acid is 2:4, you can see that they are in a 1:2 mole ratio. According to the mole ratio, the number of moles of sulfuric acid needed is twice the number of moles of aluminum. Therefore, only 0.061 mol of sulfuric acid is needed, which is less than the amount of aluminum available (0.148 mol).
Thus, sulfuric acid is the limiting reactant in this case. You can calculate the theoretical yield of aluminum potassium sulphate dodecahydrate by using the mole ratio between the limiting reactant and the product.
Moles of KAl(SO4)2·12H2O = 0.061 mol (based on limiting reactant)
Theoretical yield in grams = Moles of KAl(SO4)2·12H2O × molar mass of KAl(SO4)2·12H2O
= 0.061 mol × (2 mol KAl(SO4)2·12H2O / 2 mol) × (258.22 g/mol)
≈ 31.3 g
So, the theoretical yield of aluminum potassium sulphate dodecahydrate is approximately 31.3 grams.