Definitions
The maximum amount of product that can be produced from a given amount of reactant based on stoichiometry.
Theoretical Yield?
The actual yield is almost always higher than the theoretical yield.
False (Experimental errors usually result in less product).
Which of the following can be a reason for a low percent yield? A) Side reactions occur.
A) Side reactions occur.
B) Reactants are impure.
C) Product is lost during filtration.
D) All of the above.
D (All of the above)
If 2 moles of $A$ react to produce 2 moles of $B$, how many moles of $B$ are produced from 5 moles of $A$?
5 moles
In the reaction Mg + 2HCl ------> MgCl2 + H2, you start with 1 mole of Mg. If you collect 0.8 moles of MgCl2, what is the percent yield?
80%.
The amount of product that is actually measured and collected in a real laboratory experiment.
Actual Yield?
Mass is conserved in every chemical reaction.
True
In the equation 2H2 + O2 ------> 2H2O, what is the mole ratio of oxygen to water?
A) 1:2
B) 2:1
C) 2:2
D) 1:1
A (1:2).
How many moles are in 36 grams of H2O? ( O = 16, H = 1)
2 moles
2H2 + O2 ------> 2H2O. If you have 4.0g of H2 (Molar mass = 2.0 g/mol), how many moles of H2 do you have?
2.0 moles.
The ratio of actual yield to theoretical yield, expressed as a percentage.
Percent Yield?
o calculate percent yield, you divide the theoretical yield by the actual yield and multiply by 100.
False (It is Actual / Theoretical).
If the theoretical yield is 50g and the actual yield is 40g, what is the percent yield?
A) 125%
B) 80%
C) 10%
D) 90%
B (80%).
Calculate the molar mass of aluminium sulate Al2(SO4)3 (Al = 27, S =32, O = 16)
342 g/mol
In the reaction 2H2 + O2 -----> 2H2O, if you start with 2.0 moles of H2, what is the theoretical yield of H2O in grams? (Molar mass of H2O = 18 g/mol).
36 grams.
The study of quantitative relationships between the amounts of reactants used and products formed by a chemical reaction.
Stoichiometry?
A percent yield of 100% means that every single atom of the limiting reactant was converted into the desired product.
True
What is the first step in any stoichiometry problem?
A) Convert grams to moles.
B) Balance the equation.
C) Calculate the molar mass.
D) Measure the actual yield.
B (Balance the equation).
A reaction has a theoretical yield of 10.0g but only 7.5g is produced. What is the percent yield?
75%.
A student calculates a theoretical yield of 25g. After the experiment, the percent yield is 90%. What was the actual yield?
22.5g (25 x 0.90)
A conversion factor that relates the amounts in moles of any two substances in a chemical reaction.
Mole Ratio?
You can calculate a mole ratio using an unbalanced chemical equation.
False (The equation must be balanced).
If your percent yield is over 100%, what is the most likely cause?
A) The reaction was perfect.
B) The product is still wet (contains solvent).
C) You used too much reactant.
D) Atoms were created.
B (The product is still wet).
For N2 + 3H2 ------> 2NH3, how many moles of H2 are needed to react with 2 moles of N2?
6 moles.
2How many grams of O2 (32 g/mol) are required to react completely with 4 grams of H2 (2 g/mol) to produce water?
32 grams. (Steps: 4g H2 = 2 moles H2. Ratio is 2:1, so 1 mole O2 is needed. 1 mole O2 = 32g).