The Determination Of The Mass Of A Product Of

the determination of the mass of a product of a chemical reaction objective use grams of nahco3 and a balanced chemical equation to predict

The Determination of the Mass of a Product of a Chemical Reaction
Objective
Use grams of NaHCO3 and a balanced chemical equation to predict, then
verify the grams of NaCl produced.
Brief Overview
We will react sodium bicarbonate with an excess of hydrochloric acid.
NaHCO3 (s) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l)
A careful measurement of the mass of NaHCO3 and knowledge of the
balanced equation (above) will allow you to calculate the mass of NaCl
expected to be produced. Then, you will measure the actual amount of
NaCl you produced and compare it to the predicted amount.
Safety
1.
Make sure to wear goggles during the entire course of the lab,
which includes all clean-up time.
2.
This lab involves handling hydrochloric acid. This substance is
caustic. Be careful to avoid spills, splatter or inhalation of
vapor.
3.
If you spill any HCl solution, inform your teacher immediately.
Procedure
Day One - Reacting NaHCO3 with HCl
1.
Clean and dry a 150-mL beaker. Place the empty 150-mL beaker on
the electronic balance. Record this value in your data table.
Then, press the tare button. The balance will reset to 0.00. If it
is slightly off, wait 3 seconds, then press tare again.
2.
Remove the beaker from the balance and add one moderate spoonful
of sodium bicarbonate.
3.
Return the beaker to the electronic balance and allow the value to
become steady. Do not press tare. Record this value (the mass of
sodium bicarbonate) on your data table.
4.
Pour about 20 mL of 3-molar hydrochloric acid into a 50 or 100-mL
beaker. Place a plastic pipet in the beaker. DO NOT put the
medicine dropper down anywhere but the beaker.
5.
Add 3 drops of acid to the NaHCO3 beaker, moving the dropper so
that no drops land on each other. The key point is to spread out
the adding of acid so as to hold all splatter within the walls of
the beaker.
6.
Continue to add acid slowly drop by drop. As liquid begins to
build up, gently swirl the beaker. This is done to make sure
unreacted acid reaches unreacted sodium bicarbonate. Do not add
acid while swirling.
7.
Your goal is to stop adding acid when all bubbling has ceased.
Another way to say that is to add the minimum amount of HCl that
will react with all of the sodium bicarbonate. When you think all
bubbling has ceased, swirl the beaker and check for more bubbling.
When you think all bubbling has ceased, add ONE DROP more of acid
and swirl. If no bubbling happens, you are done. DO NOT add more
acid.
8.
Using a small amount of tape put your initials on the beaker and
place it on the tray for an overnight heating. We will resume the
lab on day 2.
9.
Throw your disposable pipet in the garbage. Pour any remaining HCl
solution down the drain with the water running. Thoroughly rinse
the 100-mL beaker with tap water. Put all glassware away. Wash
your hands.
Day Two - Heating to Constant Weight
1.
Weigh your beaker and contents on the electronic balance. Record
this weight (first weighing) in your data table.
2.
Set up ring stand, wire gauze and your beaker as shown in the
example on the center table and in the pre-lab discussion. Place a
watch glass over the beaker. Using a Bunsen burner, heat the
beaker and its contents for 3 minutes. Allow the beaker to cool.
3.
Weigh the beaker and contents (second weighing).
4.
Repeat the previous two steps (third weighing).
5.
Clean everything thoroughly, washing your hands when finished.
Data Table
Day One Data
Day Two Data
Mass
grams
Mass
grams
empty 150-mL beaker
NaCl plus beaker (heat lamp)
first weighing
NaHCO3 in beaker
NaCl plus beaker (Bunsen burner)
second weighing
NaCl plus beaker (Bunsen burner)
third weighing
Day One Calculations
*
Based upon the mass of NaHCO3 reacted and the balanced equation
given above, calculate the theoretical mass of NaCl that should
form in your reaction (Hint: Do a mass-mass problem starting with
the mass of NaHCO3 in your data table and ending with mass of
NaCl).
Day Two Calculations
1.
Determine, by subtraction, the actual mass of NaCl produced in
your experiment (use the third weighing – it is the most
reliable).
2.
Calculate your percentage yield for the reaction.
(% yield = [actual mass of product/theoretical mass of product] x
100).
3.
Provide at least one plausible reason why your percent yield did
not equal 100 % (in other words, what happened?)