Percent yield and Limiting Reactant

Percent yield and Limiting Reactant

Open Ended

In your own words, define limiting reactant and explain why it is important.

Types of reactants

Limiting Reactant (Reagent)

Limits the reaction by determining how much product can be produced.

Excess Reactant (Reagent)

Not used up completely in a reaction (leftovers)

Open Ended

Think about this scenario:

You find your grandma's recipe for your favorite kind of cookies you loved eating as a kid.

The measurements for the liquids in the recipe are all written in liters/milliliters.

You only have measuring cups that measure in teaspoon/tablesppon/cups.

What do you do to measure the correct amount of liquid?

2 Na + S -->Na₂S

GC=Grilled Cheese
Equation reads

 7 GC( $\frac{2\ Bread}{1\ GC}$ ) =14 bread

Open Ended

What about the cheese? How many slices of cheese are needed to make 7 grilled cheese sandwiches?

Answer with the format

....GC ( $\frac{.....Cheese\ slices}{.....GC}$  ) = .....Cheese slices

Types 1 and 2 always start with moles

Type 1: (Mole-Mole)
B= unknown value (what we are solving for)
A=Given value (found in the problem)
 $mol_B=mol\ known_A\ \cdot\ \frac{mol_B}{mol_A}$  

Type 2: (Mole-Mass)

 $grams_B=mol\ known_A\ \cdot\ \frac{mol_B}{mol_A}\cdot\frac{Molar\ Mass_B}{1\ mol_B}$  

Types 3 and 4 always start with mass

Type 3: (Mass-Mole)

 $mol_B=grams\ known_A\ \cdot\ \frac{1\ mol_A}{Molar\ Mass_A}\cdot\ \frac{mol_B}{mol_A}$  

Type 4: (Mass-Mass)
 $grams_B=grams\ known_A\ \cdot\frac{1\ mol\ _A}{Molar\ Mass_A}\ \cdot\frac{mol_B}{mol_A}\cdot\frac{Molar\ Mass_B}{1\ mol_B}$  

Percent Yield

 $\%\ yield\ =\ \frac{actual\ yield}{theoretical\ yield}\ \cdot\ 100$  

Actual yield is given (determined through experimentation)

Theoretical yield is determined by stoichiometry (If the reaction fully completed)

Multiple Choice

Using this problem:

Phosphorous reacts with bromine to form phosphorous tribromide. 35.0 grams of bromine are reacted and 27.9 grams of phosphorous tribromide are formed.

2 P + 3 Br₂ --> 2 PBr₃

Answer the following question:

Which of these is the actual yield of phosphorous tribromide?

• 35 grams

• 27.9 grams

• 39.5 grams

• 23.9 grams

Multiple Choice

Using this problem:

Phosphorous reacts with bromine to form phosphorous tribromide. 35.0 grams of bromine are reacted and 27.9 grams of phosphorous tribromide are formed.

2 P + 3 Br₂ --> 2 PBr₃

Answer the following question:

To solve for the theoretical yield, which type of stoichiometry must be performed?

• Type 1 (Mole-Mole)

• Type 2 (Mole-Mass)

• Type 3 (Mass-Mole)

• Type 4 (Mass-Mass)

Multiple Choice

When elements A and B react completely, they would form 100 grams of AB (ideally). However, transfer loss occured and only 80 grams formed from experimentation

What is the percent yield for this reaction?

• 20%

• 33%

• 100%

• 80%