Lab: Percent Yield
Name(s) ________________________________________
Period ______
Score _______
I: Purpose: In this experiment, you will test the Law of Conservation of Matter by causing a reaction to occur with a
given amount of reactant. You will then carefully determine the mass of one of the products. By then calculating the
theoretical mass you will determine the percent yield of the reaction.
II: Procedure:
1. Obtain a watch glass and an evaporating dish and see if the watch glass fits the evaporating dish (see picture
below). The watch glass should be slightly larger than the evaporating dish so that when fit over the evaporating
dish it sticks out over the edges “slightly”. Tell your instructor if the fit is too big or too small to see if a more
appropriate pair can be found.
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Clean the evaporating dish and a watch glass with water. Dry them thoroughly using a paper towel.
Place the evaporating dish (not the watch glass) on a hotplate and heat it using setting “10” for about 3 minutes to
insure the removal of all the moisture.
Carefully remove the evaporating dish from the hotplate and place it on a ceramic tile to allow it to cool.
After cooling measure mass of the evaporating dish to the nearest 0.01g and record this mass in your data table.
Leave the evaporating dish on the balance and do not zero the balance. With a scoop, add about 3g (somewhere
between 2.90g and 3.10g) of sodium hydrogen carbonate (NaHCO3) to the evaporating dish. Read the mass to the
nearest 0.01g and record in your data table.
Obtain about 6ml of 6M hydrochloric acid in a clean 10ml graduated cylinder.
Place the watch glass cover over the evaporating dish containing the NaHCO3.
Obtain a plastic dropper pipet and use it to gradually add the acid to the NaCHO3 in the evaporating dish through
the pour spout of the evaporating dish. Allow the drops to enter the lip of the evaporating dish so that they flow
down the side gradually.
Continue adding the acid slowly until the reaction has stopped (no more fizzing). Do not add more acid than is
needed. You may need to remove the watch glass from time to time and carefully stir the mixture in the
evaporating dish with a glass stirring rod.
Remove the watch glass cover and rinse the underside of the watch glass with a very small amount of distilled
water. Be sure to wash all material into the evaporating dish.
Place the evaporating dish on a hot plate and heat it at setting “10” until a majority of the water is boiled away.
Take care to avoid loss of liquid by boiling over. Turn the hotplate down to “4” when most of the water has
vaporized.
Continue to dry the solid slowly until it appears to be completely dry (The solid should appear to be a bright white
when dry).
Allow the dish to cool, then measure the mass to the nearest 0..01g. Record this as your initial dried mass.
Reheat the dish and contents at setting “5” for three minutes, let it cool, and remeasure the mass to the nearest
0.001g. Record this as your final dried mass.
Clean and dry the evaporating dish and watch glass. The white solid can be dissolved down the drain.
III: Data and Observations:
a.) Mass of empty evaporating dish
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b.) Mass of evaporating dish + NaHCO3
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c.) Initial dried mass of evaporating dish + white solid
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d.) Final dried mass of evaporating dish + white solid
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IV: Calculations: (You may use a piece of your own paper if you feel that you need more room).
1.
The reaction that occurred in this lab was actually a series of two reactions. The first being double replacement
and the next being a decomposition.
(a) Write the balanced equation for the double replacement reaction that occurs between and sodium hydrogen
carbonate and hydrochloric acid.
(b) One of the products of the above reaction is carbonic acid. Carbonic acid will immediately decompose after it
forms into water and carbon dioxide. Write the balanced equation for this decomposition reaction.
(c) We can combine the two equations above to get the overall equation for the reaction by cancelling out the
carbonic acid from each equation. Combine the two reactions above to determine the reactants and products
of the overall equation. Write this overall equation and balance it.
2.
Calculate the mass of NaHCO3 that you used.
3.
Using the mass of NaHCO3 that was used. Calculate the mass of NaCl that you expect to be produced.
4.
Calculate the mass of NaCl that you actually produced in the experiment.
5.
Based on the amount of NaCl that you produced, calculate the percent yield of the reaction in your experiment.
6.
If your percent yield is not 100% suggest something that could have occurred during the lab that would account for
this?
V: Problems: (You may use a piece of your own paper if you feel that you need more room).
1.
Calculate the grams of CO2 gas that would be produced from the reaction if 2.68g of NaHCO3 would have been
used and the percent yield of the reaction was 86.5%.
2.
Calculate the grams of NaHCO3 that would have been needed in the reaction to produce 1.24g of H 2O if the
percent yield of the reaction was 72.2%.