Science Buddies: "Ask an Expert"

Calculating the Molar Enthalpy of the "Volcano Experiment" (Sodium BiCarbonate and Diluted Acetic Acid)------>Basically, I have to measure the tempurature, but the reaction happens so fast, how could I do this with a Calorimeter? (I was thinking Gell Caps, but don't think I'm allowed or some sort of filter or funnel to make it go slower....).
Any Ideas? I've also never used a Calorimeter. I no the idea behind it, and basically how to set it up, but when I put the reactants in, I don't think I'll have enough time to close both lids, and put a thermometer in. :S

Suggestions?

My Procedure is due Tomorrow...


*I ONLY have to measure the heat change, nothing else ^_^ but thanks!!!

Hi Undefined,
It seems as though your procedure will depend on what equipment you have available. Have you seen the calorimeter that you are expected to use for this experiment?
One way this sort of thing is accomplished is by putting the solids in a sealed glass container, and then breaking the glass inside the sealed calorimeter. This page has a simple animation of the procedure:
http://www.chm.davidson.edu/ChemistryAp ... trate.html
I'm sure there are many other methods you could improvise, depending on the equipment available to you. You might also need to use some trial and error to find an approach that works.
Good luck!
Chris

Thanks Chris, but any glass I break I have to pay for (we don't have anything that fancy...). It's a thought though! I'll ask!

I understand. The sort of ampules used for this procedure cost about 25 cents each, but they might not be available to you.

The energy released in this reaction is not just thermal. CO2 is produced at a sufficient rate that pressures in excess of the atmospheric pressure exist. If you run the experiment in a sealed calrimeter, not only do you have to determine the temperature change, you have to determine the pressure change. If you don't contain the gas produced, you won't have anywhere close to an accurate estimate of the energy produced.

One way to control the reaction rate is to limit the amount of material reacting at the same time. One way is to disolve the sodium bicarbonate in distilled water and then use a syringe to very very slowly add the acid. Note the reaction is a two stage reaction so be sure to start very slowly so it doesn't get away from you. If you design the experiment to have an excess of acid (total amount of reaction controlled by the amount of sodium bicarbonate) and the liquids and their containers start at the same temperature, any measured temperature change will be a result of the reaction. The difficult part is to collect the gas produced so that you can make measurements and can use the ideal gas law to calculate the energy change involved in the gas production.

If you dissolve Gel Capsules in dilute acetic acid:

1. Is it endo or exothermic?
2. Does it create any significate products (significant meaning if I also had sodium bicarbonate in there reacting, would it mess up the reaction?)?

Grade 12,have grade 11 and most of grade 12 Chem.

Any help is greatly appriciated!! Thanks!!!

Hi, I merged your new topic with your old topic describing your project so that the experts can see the context of your question. Please add future questions related to this project in this same topic. Thanks.
You could address the exothermic/endothermic question about gelatin dissolution by running a control experiment with only gelatin capsules and no baking soda. The question of how gelatin affects the reaction with baking soda could be trickier. I can imagine that the gelatin might dissolve very slowly and only partially. Some baking soda might be trapped in partially dissolved gelatin & isolated from the acetic acid. My inclination is that a non-reactive container for the baking soda would probably be less problematic.
Hopefully our other experts will have some additional ideas to offer.
Chris

Try reading http://www.apple-cider-vinegar-benefits ... r.html#artand looking at the temperature vs time graph to answer your is it an endothermic or exothermic reaction wrt the sodium bicarbonate / acetic acid reaction.

Gelatin capsules are proteins chains consisting of several amino acids. I doubt there is going to be any chemical reaction involved in disolving gelatin in a weak acetic acid solution other than a physical state change and possibly some ionization changes. Essentially you have multiple solid acids in a an acqueous acid solution. Given that there is a physical state change, the heat of fusion would make this slightly endothermic (it takes some energy to melt the solid gelatin; however, some of this would be balanced by a minute amount of energy released by some ionization). I suspect that the amount of energy involved is less than what can be measured with small quantities. Unfortunately, if you increase the quantity in hopes of being able to measure it, you will have to add energy by stirring the sample in order to speed up the reaction enough to overcome any heat loss/gain in a calrimeter to the environment; however, by stirring, you are adding energy. In other words, it isn't going to be something that can be measured.