A nice quick and easy stoichiometry lab...

Stoichiometry lab

What are we doing to help kids achieve?

     I am always searching for engaging dependable good labs and I may have stumbled onto a nice stoichiometry lab.

     First, students are told that they have to determine the amount of active ingredient in an antacid tablet. Then I ask them if they have any questions. First it starts with blank stares...then slowly the questions start coming. What exactly is the active ingredient? What does it react with? They are provided information that the active ingredient is baking soda. Now they want to know the chemical formula and someone says, "How about the balanced equation?" I explain to them that the baking soda reacts with the acid in the tablet but we will use dilute hydrochloric acid to make sure it all reacts. Slowly students ask more and they start to look at the carbon dioxide. The plan then becomes to record the mass of the dilute acid solution and tablet before and after the reaction. The "after" mass should be less because carbon dioxide left the system. If they can find the mass of the carbon dioxide then they can find the moles of carbon dioxide. The balanced equation helps them connect this to moles of sodium bicarbonate and then grams of sodium bicarbonate. Usually it is a fast, easy and relatively reliable reaction. Each student group is given a portion of a whole tablet and they are able to do the reaction twice in an attempt to obtain more data. Having a portion of a tablet prevents groups from all having the same data based on one whole tablet. Once they find the grams of sodium bicarbonate in the portion of the tablets then they can find the amount in a whole tablet if provided the mass of a whole tablet. Finally, they can do a percent error because the amount of sodium bicarbonate is on the label.  

     However...there is more on the label. The label also provides the milligrams of sodium. So here is a fun twist. Students have to find the percent error and compare their amount of sodium bicarb in each tablet to the amount the manufacturer suggests...but they are only provided the amount of sodium in each tablet and told that all of this sodium is from the sodium bicarbonate in the tablet. How should they figure this out??? Hopefully, they will remember back a few weeks when we did percent composition in my class.  

Do you have a quick and easy inquiry lab that tends to work well and is a favorite "go to"?  Don't be afraid to share....




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For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).  

For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.

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