Summer Research Program for Science Teachers

Monika Biro

Professional Children’s School

2000

Mathematical and Chemical Relationships of Stoichiometric Problems

OBJECTIVE: Stoichiometry is the study of  quantitative (measurable) relationships that exist in chemical formulas and reactions.  [9-12 Content Standard B- Chemical reactions] This part of chemistry is frequently a problem for students because of the mathematical and chemical relationships of stoichiometric problems.  In this lesson plan I collected some ways to make problem-solving more interesting and practical.  Of course, solving many of these types of problems is still indispensable, but with some computer and laboratory activities it can be more fun.

COMPONENTS OF THE LESSON PLAN:

·        Cooperative learning activity

·        Laboratory exercises

COOPERATIVE LEARNING ACTIVITY

OVERVIEW:

The following group activity is a good way to review the most important key words used in stoichiometry that were learned in previous chapters.  These include mole, molar mass, possibly Avogadro’s number, and mass – mole relationships.

TIME FRAME:

One 45-minute period.

MATERIALS:

-         various different elements and/or simple compounds

-         laboratory balances

-         calculators

-         pen

-         the periodic table

-         paper

PROCEDURE:

-         set up the appropriate number of lab stations depending on the number of students in your class

-         measure the mass of each container that the chemicals were given in

-         give students the number of moles of each substance

-         let students work in groups of two-three to:

1.     measure the mass of one of the given substances

2.     determine the molar mass of the substance by using the given number of moles and the measured mass

3.     determine the identity of the substance by using the periodic table and previously learned physical characteristics [9-12 Content Standard A- Formulate explanations using evidence]

4.     the number of particles can also be determined by using Avogadro’s number

5.     students can go to other lab stations and repeat the previous procedure if more practice is needed

LABORATORY EXERCISE

TIME FRAME:

Two 45-minute periods.

OBJECTIVE:

A series of small experiments and a worksheet can be very useful in solving stoichiometry problems in the laboratory.  Here are some examples.

MATERIALS:

EXPERIMENT 1:

-         100-mL beaker

-         0.5 g fine aluminum foil or wire

-         0.1 M H2SO4

-         hot plate

-         balance

EXPERIMENT 2:

-         5 g solid sodium nitrate

-         wooden split

-         1 test tube

-         test tube tongs

-         Bunsen burner

EXPERIMENT 3:

-         pea size, cleaned sodium

-         water

-         phenolphthalein solution

-         small copper net

-         test tube

-         knife

-         forceps

-         filter paper

-         large glass container

EXPERIMENT 4:

-         5 cm zinc ribbon

-         200-mL beaker

-         wooden split

-         sting

-         balance [Teaching Standard D- Make accessible science materials]

PROCEDURE:

EXPERIMENT 1:

Measure the mass of aluminum.  Add known volume of H2SO4 to the aluminum in the beaker.  React all the aluminum.  You can also use some universal indicator to show the change in pH.  To get the mass of aluminum sulfate, evaporate the water.  Measure the mass of salt produced. [9-12 Content Standard B- Chemical reactions/Properties of matter]

EXPERIMENT 2:

Place the solid sodium nitrate into a test tube.  Hold test tube with test tube tongs.  Heat the test tube until the solid melts.  Remove the test tube from the fire.  Keep holding the test tube with tongs.  Light the wooden split and place the burning part into the liquid sodium nitrate.  If possible, perform this experiment under a fume hood or at open windows because intensive burning and smoking occurs.  (Hint:  The proper equation for the reaction is 2NaNO3 + C --- 2NaNO2 + CO2)

EXPERIMENT 3:

Clean and weigh sodium then wrap it into a fine copper net.  Do not touch sodium with bare hands.  Fill up a large glass container with water and add two or three drops of phenolphthalein solution.  Place a test tube open end down into the water.  Hold copper wrapped sodium close to the opening of the test tube to collect hydrogen gas  produced in the reaction.  After the reaction you can measure the volume of hydrogen produced.

EXPERIMENT 4:

Fill 2/3rd of the beaker with lead acetate solution.  Weigh a 5 cm long zinc ribbon.  Tie the ribbon to the wooden split so you can hang it into the lead acetate solution.  Let it stand undisturbed for about 10 – 15 minutes.

SAMPLE WORKSHEET:

 Observations Chemical equation Mass of reactant(s) Mass of product(s) Percent yield Experiment 1 Experiment 2 Experiment 3 Experiment 4