Observation of a Limiting Reagent Lab
NAME:______________________________DATE:_____________PERIOD:_______
Background:
A balanced equation shows the amount of reactants needed to make a certain amount
of products. A reaction with two reactants can have one reactant in excess amount and
the other reactant in limited amounts. The amount of one reactant used will be based
on the amount of the other reactant present. For example, water can be produced by
the following equation 2H2 + O2  2H2O.
If you have 20 liters of oxygen gas at STP then you would need 40 liters of hydrogen
gas. If you have less than the 40 liters needed then the hydrogen is the limiting reagent
and the oxygen is the excess reagent. If you have more than 40 liters then the
hydrogen is the excess reagent and the oxygen is the limiting reagent. In this lab the
limiting reagent and excess reagent will be found by a reaction between a strip of
magnesium and hydrochloric acid.
Procedure:
1) Obtain the mass of a medium size clean dry test tube.
2) Place a 1-inch strip of magnesium ribbon into the test tube. Then obtain the
mass of the test tube and magnesium.
3) Place the test tube into a test tube rack and add 10.0 milliliters of 3.0 M (this
is the molarity) hydrochloric acid into the test tube. Observe.
4) When the reaction is over dump the test tube contents into the central waste
beaker. Rinse the test tube and return to the rack. Rinse the graduated cylinder
and leave by the test tube rack.
Data:
Mass of test tube
Mass of test tube and magnesium
Mass of magnesium
Volume of acid used
Molarity of acid used
grams
grams
grams
milliliters
Molar
1) Write a balanced equation for the reaction. (Not reaction from background!!!!!)
Hint: Identify type of reaction by the reactants then predict products.)
2) Using the balanced equation, draw the test tube during the reaction. Be very
specific and label all four species from the balanced equation.
3) Draw the test tube at the end of the reaction. Be very specific and label all
species.
Show all work and label all units! Box your answer!
Do this as a class with the teacher.
Calculations:
1) Moles of magnesium used.
2) Moles of acid used.
(Molarity of Acid) x (Volume of Acid in Liters) = Moles of Acid
3) From the balanced equation, what is the mole ratio of magnesium to acid?
__________ mole(s) Mg to ____________ moles(s) HCl
4) Moles of magnesium needed, based on the moles of acid used.
5) Moles of acid needed, based on the moles of magnesium used.
6) Based on the calculations in # 4 and # 5, what is the limiting and excess
reagent?
Limiting Reagent ________________
Excess Reagent ________________
7) Using the limiting reagent found above, does the drawing for the end of the
reaction support your calculations? Why or why not?
Practice Problem
A piece of zinc metal weighing .40 grams is placed into 25.0 milliliters of a 1.0 molar
hydrochloric acid solution. Find the limiting and excess reagent.
Limiting Reagent ____________ Excess Reagent ____________
Teaching Notes: Observation of a Limiting Reagent
At each lab station:
Test tube rack
Medium size test tube
1 25-mL graduated cylinder
1 stirring rod
At a Central Location:
3 Molar Hydrochloric acid solution
Magnesium Ribbon
Scissors
Rulers
Waste Container: Large Beaker labeled waste
Teaching Tips:
This lab does not need the entire period. Proper dress and goggles are required and the
students should be advised on working with the 3 molar acid. For additional safety the
acid should be placed into a plastic bottle container and kept under a hood. The
students should be instructed to take their graduated cylinder to the hood and obtain
their acid there. This will keep the acid under the hood and away from individual lab
tables. A plastic bottle will not shatter if accidentally dropped. Students should be
advised to take their test tube and dump the contents into a waste beaker when
finished and then carefully rinse the test tube.
Before doing this lab experiment, students should be able to do basic stoichiometry
problems dealing with finding the limiting reagent and excess reagent. A follow-up
demonstration could be done the next day using three small flasks (125-mL) with a
balloon on top. The three flasks could contain either vinegar or hydrochloric acid with
either an antacid tablet or metal (Mg or Zn) placed into each. Set up the three flasks in
order to have one with the acid limiting, one with the acid in excess and one exactly
meeting the correct stoichiometry in order not to have a LR or ExR. Then discuss the
size of the balloons in the context of stoichiometric ratios and the amount of gas
product produced. There are two quizzes depending on the level of the student.
Students should read the conclusion and do the balanced equation under the data
section before being dismissed to the lab area. Students could also be asked to do the
practice problem on the backside of the lab or this could be done together as a class
problem.
Reference: DiSpezio, M.; Hall, T.; Schrader, C.; Young, J.; Heath Chemistry Laboratory
Experiments. D.C. Heath, Lexington, MA; 1987
Observation of a Limiting Reagent
NAME:_______________________________DATE:_____________PERIOD:_______
Background:
A balanced equation shows the amount of reactants needed to make a certain amount
of products. A reaction with two reactants can have one reactant in excess amount and
the other reactant in limited amounts. The amount of one reactant used will be based
on the amount of the other reactant present. For example, water can be produced by
the following equation 2H2 + O2  2H2O.
If you have 20 liters of oxygen gas at STP then you would need 40 liters of hydrogen
gas. If you have less than the 40 liters needed then the hydrogen is the limiting reagent
and the oxygen is the excess reagent. If you have more than 40 liters then the
hydrogen is the excess reagent and the oxygen is the limiting reagent. In this lab the
limiting reagent and excess reagent will be found by a reaction between a strip of
magnesium and hydrochloric acid.
Procedure:
1) Obtain the mass of a medium size clean dry test tube.
2) Place a 1-inch strip of magnesium ribbon into the test tube. Then obtain the mass of
the test tube and magnesium.
3) Place the test tube into a test tube rack and add 10.0 milliliters of 3.0 M hydrochloric
acid to the test tube. Observe.
4) When the reaction is over dump the test tube contents into the central waste
beaker. Rinse the test tube and return to the rack. Rinse the graduated cylinder and
leave by the test tube rack.
Data:
Mass of test tube
Mass of test tube and magnesium
Mass of magnesium
Volume of acid used
Molarity of acid used
Write a balanced equation for the reaction.
Varies
Varies
0.027
10
3.0
grams
grams
grams
milliliters
Molar
1 Mg (s) + 2 HCl (aq)  1 MgCl2 (aq) + H2 (g)
Using the balanced equation, draw the test tube during the reaction. Be very specific
and label all four species from the balanced equation.
Mg strip with bubbles coming off labeled H2 gas. Aqueous layer labeled HCl and MgCl2.
Draw the test tube at the end of the reaction. Be very specific and label all species.
Test tube should have MgCl2 and HCl labeled in an aqueous layer.
Show all work and label all units!
Calculations:
1) Moles of magnesium used.
0.027 grams
1 mole Mg
24.3 grams
2) Moles of acid used.
M x L = moles
= 0.0011 moles Mg
3.0 M x .010 L = 0.03 moles HCl
3) From the balanced equation, what is the mole ratio of magnesium to acid?
____1______ mole(s) Mg to _____2_______ moles(s) HCl
4) Moles of magnesium needed, based on the moles of acid used.
0.03 moles HCl
1 mole Mg
2 mole HCl
= 0.015 moles Mg
5) Moles of acid needed, based on the moles of magnesium used.
0.0011 moles Mg
2 moles HCl
1 mole Mg
= 0.0022 moles HCl
6) Based on the calculations in # 4 and # 5, what is the limiting and excess
reagent?
Limiting Reagent Magnesium (Mg)
Excess Reagent
Hydrochloric acid (HCl)
7) Using the limiting reagent found above, does the drawing for the end of the
reaction support your calculations? Why or why not?
Yes the picture does not show the LR which runs out during the reaction.
Practice Problem:
A piece of zinc metal weighing .40 grams is placed into 25.0 milliliters of a 1.0 molar
hydrochloric acid solution. Find the limiting and excess reagent.
Limiting Reagent ___Zn_________ Excess Reagent ____HCl________
2 HCl(aq) + 1 Zn(s)  1 ZnCl2 (aq) + 1 H2 (g)
M x L = moles
1.0 M x .025 L = 0.025 moles HCl
0.40 grams
1 mole Zn
65.4 grams = 0.0061 moles Zn HAVE
0.025 mol HCl
1 mole Zn
2 mole HCl
= 0.0125 mole Zn NEEDED
Observation of a Limiting Reagent Quiz
NAME:______________________________DATE:_____________PERIOD:_______
1.
Which two products were formed when hydrochloric acid and magnesium reacted
in the Observation of a Limiting Reagent lab?
a. hydrochloric acid & magnesium
b. hydrogen gas & magnesium
c. hydrogen gas & magnesium chloride
2.
Which type of reaction was seen in the Observation of a Limiting Reagent lab?
a. SR
b. DR
c. IC
d. CC
e. S
For questions 3-8, a student reacts 130.8 grams of zinc metal with 500 mL of 2 M
hydrochloric acid, using the following balanced equation.
moles
Remember, for a liquid, M x L = moles or M =
.
liter
Zn + 2 HCl  ZnCl2 + H2
3.
How many moles of zinc does the student have?
a. 2.0 mol
b. 1.0 mol c. 0.5 mol d. 13 mol
e. none of these
4.
How many moles of HCl does the student have?
a. 1000 mol
b. 100 mol c. 10 mol
d. 1 mol
e. none of these
5.
6.
7.
8.
How many moles of zinc does the student need?
a. 2.0 mol
b. 1.0 mol c. 0.5 mol d. 130.8 moles
Which is the limiting reactant?
a. zinc
b. hydrochloric acid
c. zinc chloride
How many liters of hydrogen gas can be produced?
a. 11.2 L
b. 22.4 L
c. 44.8 L
d. 224 L
e. none of these
d. hydrogen
e. none of these
How many moles of the excess reactant will be left over?
a. 0.5 mol
b. 1.0 mol
c. 1.5 mol d. 2 mol
e. none of these
Observation of a Limiting Reagent Quiz Answer Key
NAME:______________________________DATE:_____________PERIOD:_______
1) Which two products were formed when hydrochloric acid and magnesium reacted in
the Observation of a Limiting Reagent lab?
a. hydrochloric acid & magnesium
b. hydrogen gas & magnesium
c. hydrogen gas & magnesium chloride
2) Which type of reaction was seen in the Observation of a Limiting Reagent lab?
a. SR
b. DR
c. IC
d. CC
e. S
For questions 3-8, a student reacts 130.8 grams of zinc metal with 500 mL of 2 M
hydrochloric acid, using the following balanced equation.
moles
Remember, for a liquid, M x L = moles or M =
.
liter
Zn + 2 HCl  ZnCl2 + H2
3) How many moles of zinc does the student have?
a. 2.0 mol
b. 1.0 mol c. 0.5 mol
d. 13 mol
e. none of these
4) How many moles of HCl does the student have?
a. 1000 mol
b. 100 mol c. 10 mol
d. 1 mol
e. none of these
5) How many moles of zinc does the student need?
a. 2.0 mol b. 1.0 mol c. 0.5 mol d. 130.8 moles
6) Which is the limiting reactant?
a. zinc b. hydrochloric acid
c. zinc chloride
e. none of these
d. hydrogen
7) How many liters of hydrogen gas can be produced?
a. 11.2 L
b. 22.4 L
c. 44.8 L
d. 224 L
e. none of these
8) How many moles of the excess reactant will be left over?
a. 0.5 mol
b. 1.0 mol
c. 1.5 mol d. 2 mol
e. none of these
Observation of a Limiting Reagent Quiz
NAME:______________________________DATE:_____________PERIOD:_______
1) Which two products were formed when hydrochloric acid and magnesium reacted in
the Observation of a Limiting Reagent lab?
a. hydrochloric acid & magnesium
b. hydrogen gas & magnesium
c. hydrogen gas & magnesium chloride
2) Which type of reaction was seen in the Observation of a Limiting Reagent lab?
a. SR
b. DR
c. IC
d. CC
e. S
For questions 3-8, a student reacts 130.8 grams of zinc metal with 500 mL of 2 M
hydrochloric acid.
3) How many moles of zinc does the student have?
a. 2.0 mol
b. 1.0 mol c. 0.5 mol d. 13 mol
e. none of these
4) How many moles of HCl does the student have?
a. 1000 mol
b. 100 mol c. 10 mol
d. 1 mol
e. none of these
5) How many moles of zinc does the student need?
a. 2.0 mol
b. 1.0 mol c. 0.5 mol d. 130.8 mol e. none of these
6) Which is the limiting reactant?
a. zinc
b. hydrochloric acid
c. zinc chloride
7) How many liters of hydrogen gas can be produced?
a. 11.2 L
b. 22.4 L
c. 44.8 L
d. 224 L
d. hydrogen
e. none of these
8) How many moles of the excess reactant will be left over?
a. 0.5 mol
b. 1.0 moles c. 1.5 mol d. 2 mol
e. none of these
Observation of a Limiting Reagent Lab Make-up
NAME:______________________________DATE:_____________PERIOD:_______
Background:
A balanced equation shows the amount of reactants needed to make a certain amount
of products. A reaction with two reactants can have one reactant in excess amount and
the other reactant in limited amounts. The amount of one reactant used will be based
on the amount of the other reactant present. For example, water can be produced by
the following equation 2H2 + O2  2H2O.
If you have 20 liters of oxygen gas at STP then you would need 40 liters of hydrogen
gas. If you have less than the 40 liters needed then the hydrogen is the limiting reagent
and the oxygen is the excess reagent. If you have more than 40 liters then the
hydrogen is the excess reagent and the oxygen is the limiting reagent. In this lab the
limiting reagent and excess reagent will be found by a reaction between a strip of
magnesium and hydrochloric acid.
Procedure:
1) Obtain the mass of a medium size clean dry test tube.
2) Place a 1-inch strip of magnesium ribbon into the test tube. Then obtain the mass of
the test tube and magnesium.
3) Place the test tube into a test tube rack and add 10.0 milliliters of 3.0 M hydrochloric
acid into the test tube. Observe.
4) When the reaction is over dump the test tube contents into the central waste
beaker. Rinse the test tube and return to the rack. Rinse the graduated cylinder and
leave by the test tube rack.
Data:
Mass of test tube
Mass of test tube and magnesium
Mass of magnesium
Volume of acid used
Molarity of acid used
20.000 grams
20.027 grams
10
3
grams
milliliters
Molar
Write a balanced equation for the reaction.
Using the balanced equation, draw the test tube and label where all four species would
be during the reaction.
Using the limiting and excess reagent calculated on the back draw the test tube and
species that would be present at the end of the reaction.
Show all work and label all units! Box your answer!
Calculations:
1) Moles of magnesium used.
2) Moles of acid used.
(Molarity of Acid) x (Volume of Acid in Liters) = Moles of Acid
3) From the balanced equation, what is the mole ratio of magnesium to acid?
__________ mole(s) Mg to ____________ moles(s) HCl
4) Moles of magnesium needed, based on the moles of acid used.
5) Moles of acid needed, based on the moles of magnesium used.
6) Based on the calculations in # 4 and # 5, what is the limiting and excess reagent?
Limiting Reagent ________________
Excess Reagent ________________
7) Using the limiting reagent found above, does the drawing for the end of the reaction
support your calculations? Why or why not?
Practice Problem
A piece of zinc metal weighing .40 grams is placed into 25.0 milliliters of a 1.0 molar
hydrochloric acid solution. Find the limiting and excess reagent.
Limiting Reagent ____________ Excess Reagent ____________
Observation of a Limiting Reagent Problem Activity
NAME:______________________________DATE:____________PERIOD:_______
What does the word antacid mean? What are some commercial brand antacid tablets?
Why do people take antacid tablets?
Problem: Can the effectiveness of antacid medication be measured by observation of a
limiting or excess reagent reagent?
Procedure:
1) Obtain three 250-mL beakers and place 50.0 mL of vinegar into each beaker.
2) Add 10.0-mL of red cabbage juice indicator or universal indictor to each beaker.
3) Add 1 tablet of different antacids to each beaker. Observe.
Information:
Red cabbage juice indicator is red to rose color in acidic conditions, purple in neutral and
goes from blue-green-yellow as basic conditions increase.
Universal indicator: See chart for color match and pH
Data Table & Observations:
Conclusion/Explanation:
Research Questions: Why are there so many different antacid medications? Are there
advantages or disadvantages of taking one type of antacid tablet as compared to a
different type of antacid tablet?