Lab #6 – Aqueous solution to mass, a mole ratio lab, with and an
introduction to limiting reagent theory.
In this lab, we will examine the following reaction.
Will escape as steam
during heating
NaHCO3(s) + HCl(aq)  CO2(g) + H2O(l) + NaCl(s)
A reactant, will be
consumed in the
reaction.
A solution of known
molarity, the volume
used is your data.
Escapes as gas
bubbles,
effervescence.
The solid product, will be
collected at after the other
products escape as gasses.
We will add a known volume and molarity of HCl to a known mass of NaHCO3
to obtain the objective, the solid product NaCl. The moles of HCl reacted can be
converted to moles. The moles of HCl will be used to solve for moles of NaCl by using
the mole ratio calculation. Grams of NaCl can be calculated from the theoretically
calculated mole quantity of NaCl, and then compared to the experimentally measured
mass.
PROCEDURE
1) Obtain an evaporating dish, clean the dish well and heat to constant mass. Record
the mass in your lab notebook. NOTE-some of the dishes may be stained, this
will not affect your data.
2) Obtain a watch glass and clean it well. Dry it with paper towels and record the
mass in your notebook.
3) Mass about 5.0 grams of NaHCO3(s), record its exact mass in your lab book.
Place the NaHCO3(s) in your evaporating dish and set aside.
4) Obtain about 30.0 mL of 6.0 mole/liter(M) HCl. Carefully determine the volume
in a graduated cylinder, then transfer it to a small beaker. The beaker will supply
the HCl for step #5). NOTE- this solution is very caustic, store it in your sink
when not in use to contain any spills. Wear gloves, if you are exposed to the acid
solution, see me immediately.
5) Use a plastic disposable pipette to slowly add the HCL solution DROPWISE from
the small beaker to the solid NaHCO3(s) in your dish. The reaction will become
effervescent (“fizzing”) as CO2 is evolved, so go slowly to avoid splatter. It is
vital that you mix the reaction by agitating the dish well after each few drops.
Record the volume of HCl solution you used by subtracting your initial volume
from what is left in the beaker.(final volume). Determine the final volume of HCl
by transferring the unused portion to a graduated cylinder. NOTE- keep your
goggles on!
6) As you slowly add HCl, the solid will dissolve and the effervescence will become
less vigorous, you are approaching the completion of the reaction. You are
finished when the bubbling JUST stops, so add HCl very slowly at this time. Do
not add more acid then needed, as it will produce a caustic odor in the next step.
7) Place the dish on a ring stand with wire pad over a Bunsen burner. Place the
watch glass on the dish in such a way as to allow a space near the lip of the dish,
you will see steam escape here during the heating. Heat the dish SLOWLY and
allow the water to evaporate. IF you heat too quickly, your product will splatter
and reduce your yield, be careful!
8) Continue to heat slowly until escaping steam is not detected. At this point the salt
will have formed a crust under the watch glass, and you may not be able to see the
product in the dish. Heat till constant mass is achieved and record the final mass
of the product in the dish covered by the watch glass. To get the mass of your
product (NaCl), subtract the mass of the clean dish and watch glass from the mass
of the dish, watch glass and product at the end of the heating process.
An outline of the calculations is:
M=moles/liters
Use the volume and
molarity of HCl to get
moles used.
Ratio moles of HCl to
NaCl to find moles of
NaCl, the ratio is 1:1
Convert moles of NaCl from
step two into grams for
theoretical yield.