Name ________________
Chemistry
Period ___
Date _________________
5.
LIMITING REACTANT LAB
Chemical reactions are represented by balanced chemical equations. For
example, the coefficients of a balanced equation indicate the number of
moles of each substance, both reactant(s) and product(s), involved in the
reaction; therefore, the ratio of moles of a substance to moles of any other
substance in the reaction can be determined at a glance.
Often reactants are added to a reaction vessel in amounts different from the
molar ratio given by the chemical equation. In that case, only one of the
reactants is completely consumed at the end of the reaction. The limiting
reactant is the reactant that is entirely consumed when a reaction goes to
completion. Other reactants are in excess and remain partially unreacted.
The moles of product, however, are always determined by the moles of
limiting reactant.
In this experiment, iron filings will be added to an aqueous solution of
copper (II) sulfate. A single replacement reaction will take place, according
to the following balanced chemical equation:
Fe(s) + CuSO4(aq)  Cu(s) + FeSO4(aq)
You will determine through calculations which reactant is the limiting
reactant and therefore what the theoretical yield of copper should be. You
will then compare this value to the actual yield of copper from the
experiment.
Procedure
1. Write your name & period on a piece of clean, dry weigh paper.
Mass the paper.
2. Fold the filter paper in half (“taco”) and in half again
(“quesadilla”) and place it into the glass funnel. Set aside.
3. Mass 4.00 g of copper (II) sulfate crystals and pour it into a 100
mL beaker.
4. Measure 50 mL of water using the graduated cylinder and add it to
the crystals. While you work on steps 5 and 6, your lab partner
should do step 7.
6.
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14.
Set up your ring stand, iron ring and wire mesh. Place the beaker
on the wire mesh. Heat your mixture to just below boiling. You
will want to keep a medium-low flame so that the contents of the
beaker DO NOT BOIL.
Continue heating and gently stir the mixture until the crystals are
completely dissolved. Turn off the gas and move the burner out of
you way.
Measure precisely 1.12 g iron filings.
While stirring gently, add the iron in small amounts to the hot
copper (II) sulfate solution. When all of the iron has been added
and mixed thoroughly, allow the beaker to sit for 10 minutes while
the reaction proceeds. Make sure the stirring rod does not have
any solid on it when you remove it from the solution. Do not
disturb the solid at the bottom of the beaker. Record your
qualitative observations.
Carefully and with a steady hand, decant (pour off) the liquid into
a 250 mL beaker. Do not disturb the solid at the bottom of the
beaker.
Add approximately 10.0 mL of water to the solid in the 100 mL
beaker. Stir or swirl well. Let the solid settle for 3 minutes.
Decant the liquid.
Add approximately 10.0 mL of water to the solid again. Swirl.
Hold the filter paper/funnel over the 250 mL beaker and pour the
contents of the 100 mL beaker through the filter paper. Pour
slowly - - do not fill the paper more than three quarters full. Allow
the liquid to filter through, trapping the solid. Any solid that
remains in the beaker should be washed into the filter paper: tip
the beaker and squirt water into the beaker such that the solid will
flow into the filter paper. Be sure all solid is trapped in the filter
paper or you will have considerable error.
Place your filter paper and solid in the designated drying area and
allow it to dry overnight.
Pour the decant down the sink and wash all glassware. Throw any
garbage away.
DAY 2
15. Mass the filter paper and solid.
1. Briefly state your hypothesis. Your hypothesis should be based on your
determination of the limiting reactant. Prove this through calculations.
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Calculations:
Data and Observations
Before you come to class/ lab, create your data table(s) using a straight-edge
ruler. For your quantitative data table, be sure to create columns and rows
that are clearly labeled (include units) and provide space for all key data.
For your qualitative data table, be sure to leave enough space for neatly
written descriptions of your observations.
2. Calculate the percent yield of copper. Write a formula, plug in
and solve.
3. Calculate the mass of the reactant in excess that remains after the
reaction was complete.
Analysis
1. Which reactant was the limiting reactant? Why/how is this
relevant to the outcome of the lab?
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2. Distinguish between the terms: theoretical yield, actual yield, and
percent yield. Is it possible to get more than 100% yield? Explain.
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Conclusion
Calculations
1. Find the mass of the copper you actually produced in the reaction,
“actual yield.”
1. A balanced chemical equation can be likened to a recipe used in a
kitchen. Relate the concept of the limiting reactant and reactant in
excess to a simple recipe of your choosing.