Percent Yield Lab Review
Common Mistakes
and
Tips for Improvement
Overall
 Organization & Neatness
 Title – appropriate and describes the lab
 Correct Order
 Headings
 Organized Calculations
 Written in third person
Introduction
 Describe the reaction (double displacement)
- how do you know?
- use what you’ve learned to describe the
reaction.
 WRITE the chemical equation*
 What will you be doing in the lab?
 Calculating Percent Yield - Give a brief outline of
how you will do that. What information do you
need to gather from the lab?
 Do not summarize results!! (=Abstract)
Materials List
 Missing sizes of equipment (beakers and
Erlenmeyer flasks)
 Include quantities of chemicals required
Safety
 Do some research
 Personal Protective Clothing
 WHMIS labels and safe handling
 ie. What to do about spills? Washing hands
after the experiment. Etc.
 Disposal*
 MSDS – You can find the MSDS for each of
the chemicals to see the above
information. If you cannot find it, come
see me.
Procedure
 For a formal lab report - write the
procedure in PAST TENSE
 When planning - write in present tense
 **Not enough detail (especially if
someone were to replicate the lab). Hard
to follow.
 Some steps are too long – break it down
into simpler terms
 Stating sizes of equipment being used
 *Don’t forget to include apparatus set up
Data/Observations
 Since there weren’t any trials conducted
there would be no need for a large, formal
data table
 BUT organize the information – create a
simple table for the data you will be
measuring and need to make note of
during the lab
Example:
Include a title (Table 1:___)
Material
Mass (g)
CuSO4 (s)
Zn (s)
Filter Paper
Filter Paper + Products
***DO NOT INCLUDE ANY TYPE OF
CALCULATION IN YOUR DATA TABLE
(except for averages if required)
Qualitative Observations
 Make sure it is organized
 Make a table or use headings
Example:
Include a title (Table 2:___)
Before Reaction:
-
During Reaction:
-
After Reaction:
-
Point form is sufficient – and easier to follow
Calculations:
 Should be organized, neat, and easy to
follow.
 Include formulas and units
 In order to calculate percent yield, first
need to calculate the mass of JUST the
product produced.
Calculations continued:
1. Calculate the mass of product produced *
2. Calculate the moles available of each
reactant
3. Determine the limiting reactant
4. Determine the theoretical mass of product
that should be produced
5. Calculate the percent yield
Analysis:
 Point of this lab was to calculate percent yield and to
see if the changes in your procedure/lab technique
would improve your percentage yield!
 DISCUSS your results
 What do your results mean? What concepts of chemistry have
you learned or can you research to explain why you got those
results?
 What does it mean to have a percent yield greater than or lower
than 100%?
 Any reasons why the mass of product produced was so high or so
low?
 Did the changes you made to your procedure improve your
percentage yield? Why or why not?
 Question #1 & 2 – the calculations were in the section
above. You just need to discuss these questions in your
analysis. Leave it in paragraph format. Mention
limiting/excess/what the product is etc...This is all part of
DISCUSSING YOUR RESULTS.
Conclusion
 discuss at least 3 sources of error and improvement to
these errors (this answers Q3). Be specific on errors
that would affect the % yield.
 Focus on equipment and procedure and not human error.
You can mention human error if something went
particularly badly.
 This is also where you would mention any problems you
had with the procedure you created. What worked or
didn’t. Did they affect your results? How?