Determine the Percentage Composition of a Mixture
Purpose: To determine the percentage composition of a mixture.
Background: You will be given a mixture of sand (silicon dioxide) and salt (sodium
chloride). The purpose of the experiment is to determine what percentage of the mixture’s
mass is due to each of the various substances.
Procedure:
NOTE: Consult safety information and obtain teacher approval before beginning the
experiment.
Design an experiment to determine the percentage composition of the mixture.
There are also some laboratory techniques that you should be familiar with before you
begin your procedure. Please read p. 13-15 of you laboratory manual BEFORE you
begin writing your procedure (Pouring Liquids, Filtering a Mixture, Using a Gas
Burner, and Heating Liquids in a Beaker).
Safety Information: Read the MSDS (Materials Safety Data Sheet) for each of the
chemicals before you begin.
Materials: You will be given the following materials. You may or may not use all of the
materials in the procedure. Make sure that you know the function or each piece of
equipment before you begin. (See p.11-12 of your laboratory manual). If your
procedure includes materials not found on this list, please consult with Mrs.
Westmoreland.
Sample of the Mixture
Beakers (250-mL or 400-mL)
Bunsen burner
Ring stand
Ring clamp
Wire gauze
Watch glass
Evaporating dish
Buchner Funnel
Stirring rod
Filter paper
Beaker tongs
Distilled water
Balance
A laboratory report will be completed in your composition book for this experiment.
It should include:
1.
2.
3.
4.
5.
Descriptive title
Purpose
List of Materials
A summary of the safety hazards associated with each of the chemicals used.
A clear, concise description of your procedure. The procedure should be written
in such a way that a student from another chemistry class in another school could
follow it.
6. A data table of your own design. Draw a data table using a straight. It should be
easy to read and labeled with units where necessary. REMEMBER: ALL MASS
MEASUREMENTS SHOULD BE RECORDED TO THE HUNDREDTH OF A
GRAM!
7. Calculations to find the percent composition of your sample of the mixture.
Calculations can be hand written (in black ink). They must be clearly labeled with
proper units and follow the rules of significant figures. Find the percentage of
sand (recovered) out of the total mixture mass. Find the percentage of salt
(recovered) out of the total mixture mass. And find the sum of the recovered
components (NaCl + SiO2) out of the total mixture mass.
8. Conclusion should be written in paragraph form (complete sentences). It should
contain a statement of the generalizations that you can draw as a result of your
experiment. Analyze all possible sources of error. Suggest improvements to your
procedure to help minimize sources of error.
You may want to include a discussion of the following questions in your
conclusion:
PLEASE DO NOT COPY THE QUESTIONS, ANSWER THEM IN
COMPLETE SENTENCES WITH THE QUESTION RESTATED.
a. If all the students in the class received a sample of the same mixture,
should each team obtain the same result for its percentage composition?
Why?
b. If the purpose of the experiment was to determine the percentage
composition of a compound, rather than a mixture, should each team
obtain the same results for the percentage composition? Why?
c. Does your experiment use physical changes or chemical changes to
separate components of the mixture?