Experiment No: 3
Mole and Mass Relationships
A Stoichiometry Lab
Pre-Lab Discussion:
In a balanced chemical equation, all reactants and products must be represented by symbols or
formulas. The total number of atoms of each element must be the same on each side of the equation to
satisfy the law of conservation of mass.
A calculation of the molar mass of a reactant or product enables a researcher to convert from
grams of a particular substance taking part in a reaction to moles of that substance. The mole
relationship given by the coefficients of the balanced equation then allows the researcher to calculate
how many moles of every other substance will take part in the reaction.
In this experiment, you will investigate the quantitative relationships in the reaction:
NaHCO3 (s) + HCl(aq)  NaCl(aq) + CO 2 (g) + H 2 O(g)
A known mass of sodium hydrogen carbonate will be reacted with excess hydrochloric acid. Knowing
the mass of NaHCO3(s) that reacts, you can determine from the balanced equation the mass of NaCl
that should be produced. You can compare this theoretical value with the actual experimental mass of
NaCl produced.
This experiment should aid in the understanding of the mole-mass relationships that exist in a
chemical reaction and in the interpretation of a balanced chemical equation.
Purpose:
The purpose of this laboratory experiment is to compare the experimental mass of a product of
a chemical reaction with the mass predicted for that product by calculation.
Equipment:
balance
burner
evaporating dish
watch glass
microspatula
ring stand
iron ring
wire gauze
safety goggles
apron
Materials:
6 M hydrochloric acid in dropper bottles
sodium hydrogen carbonate (sodium bicarbonate, NaHCO3)
Safety:
Handle the hydrochloric acid with care. Flush any spills with
cold water and a dilute solution of sodium bicarbonate and report them
to your teacher. Do not lean over the apparatus when heating it in step
7. Wear your goggles and aprons.
Procedure:
1. Wash your equipment: evaporating dish, watch glass, microspatula.
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Figure 1
2. Flame dry a clean evaporating dish by heating it in the hot part of a burner flame for about 5
minutes. Allow the dish to cool.
3. Find the combined mass of the dry evaporating dish plus the dry watch glass. Record the mass in
your data table.
4. Tare the balance. Carefully (without spilling any NaHCO3 on the scale) weigh 2.50 g of sodium
hydrogen carbonate into the evaporating dish using a microspatula. Record the mass in your data
table.
5. Set up the ring stand, iron ring, and wire gauze as shown in Figure 1. Place the watch glass on top
of the evaporating dish and place the dish on the wire gauze. DO NOT light the burner yet.
6. Obtain 6M HCl acid. CAUTION: Handle this acid carefully.
6M is a way of expressing
It can cause painful burns if it touches your skin.
concentration. It is read, “six
Using the dropper, slowly add HCl to the NaHCO3 in the
molar hydrochloric acid”.
evaporating dish, a few drops at a time. See Figure 2. Do this
The higher the number, the
while lifting back the evaporating dish slightly in order to keep all
more
concentrated the acid.
spattering materials inside the dish. Continue adding acid until the
reaction (bubbling) stops. Carefully tilt the
evaporating dish back and forth a couple of
times to make sure that the acid has contacted
all the NaHCO3. After making sure that all
bubbling has stopped, remove the watch glass
and place it curved side up on the lab bench.
7. Holding the burner in your hand, gently
heat the evaporating dish. Use a low flame
and move the burner back and forth to avoid
spattering. DO NOT LEAN over your
experiment while heating. When almost all
the liquid is gone, remove the burner and
Figure 2
replace the watch glass on the evaporating
dish, leaving a small opening for vapor to
escape. Heat gently again until no liquid remains. Allow the dish to cool completely.
8. Find the combined mass of the evaporating dish, watch glass, and product. Record the mass in your
data table.
Observations and Data:
mass (grams)
evaporating dish and watch glass
sodium bicarbonate (NaHCO3)
evaporating dish, watch glass, and product (NaCl)
product (NaCl)
Observations worth noting: ____________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Calculations and Questions:
1. Find the mass of the solid product, NaCl. Enter your results in your data table.
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2. Why can we assume that the solid product left over at the end of the reaction is only NaCl and not
any of the other products produced in this reaction? ________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
3. According to the balanced equation for the reaction used in this experiment, calculate the mass of
NaCl you would expect to get when 2.50g of NaHCO3 is reacted with an excess of HCl. (Show your
work and report this with the correct number of significant figures.)
4. How does this value compare with the NaCl mass you attained experimentally? _______________
__________________________________________________________________________________
__________________________________________________________________________________
5. What is your percent yield for this lab?
(Show your work and report this with the correct
number of significant figures.)
percentage yield =
actual yield
x 100%
theoretical yield
6. Name at least two errors that could make your percent yield too high and sometimes go above
100% in this experiment? (Human error is NOT acceptable!)
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7. Name at least two errors that could make your percent yield too low and go below 100% in this
experiment? (Human error is NOT acceptable!)
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
8. What is one thing that you think may have happened to cause your results to be the wrong percent
yield in this experiment?

Show your work and report your answers with the correct number of significant figures.
9. In the chemical reaction CaCO3  CaO + CO 2 , if 40.0g of CaCO3 is decomposed,
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A. how many grams of CaO is produced?
B. how many grams of CO2 is produced?
10. In the reaction N 2 + 3H 2  2NH 3 , if 20.0g of hydrogen reacts,
A. how many grams of ammonia is produced?
B. how many grams of nitrogen reacts?
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