Reaction Yield

Question 1

Theoretical vs. Actual Yield

Answer 1

• Theoretical yield is the mass of product predicted based on the stoichiometry of the chemical equation
  Calculated value
• Actual yield is the mass of the product actually collected during an experiment
  Measured value

Question 2

Reaction reversibility

Answer 2

• Some reactions have a competing reverse reaction
• Product being made breaks down (reverse of each other)
• Chemists try to optimize (temp, pressure) reaction conditions to minimize the extent of a reverse reaction
• Crabonic acid

Question 3

The experimental procedure

Answer 3

• No matter how careful chemists are, small quantities of material will be lost
• Mass of a reactant can be lost after its measured
  Recants being left of the scale
• Mass of the product can be lost before its measured
  Not all the product being filtered through filter paper

Question 4

how to reduce loses in experimental procedure

Answer 4

• Improving their skills
• Use better equipment
• Reducing the # of steps in a procedure
• Repeating certain parts of a procedure to increase collection yield
  Filtering the substance more than once to get product

Question 5

Impurities

Answer 5

• Not all chemicals are 100% pure/grade, they vary in grades
• This does not mean they are contaminated
• The calculated mass does not take into account of true mass of a reactant
• As chemicals age, they can become impure if not stored properly
• For example, they can absorb H2O (sodium hydroxide) in air or oxidize (magnesium)

Question 6

Competing side reactions

Answer 6

• Competing reactions prevent some of the reactants form being into their products
• When compound A reacts with compound D, there is less of compound A to react with reactant B, reducing actual yield
• P + Cl → PCl3
• PCl3 + Cl → PCL5

Question 7

Percentage Yield

Answer 7

• Tells you how efficient/successful a reaction is at covering reactants into products by comparing actual yield to theoretical yield
• percentage yeild= actual yelid/therotical yeild x 100

Question 8

Percent Error

Answer 8

• Percent error is the difference between 100% - percentage yield

Question 9

Why don’t we always get what we calculated (ie. theoretical yield)?

Answer 9

Reaction reversibility
The experimental procedure
Impurities
Competing side reactions