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At school today, we were doing experiments with ammonium nitrate and sodium hydroxide, and mixing them with water into an Erlenmeyer flask (separate flasks, of course). My instructor told us that we had to keep a styrofoam plate under the Erlenmeyer flask at all times.

After the experiment, she told us to find out why we put a styrofoam plate under the flask by tomorrow or we would get a 0 on that assignment.

Does anyone know why? I'm thinking it's to protect the table from the heat or coldness of the flask, or to protect the table in case of spills. We have to get the question exactly as she wants it, so I am looking for help.

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    $\begingroup$ What observation did you make during/after the experiment? The zero sounds harsh but the question is a good one. $\endgroup$ – bpedit Oct 10 '16 at 22:00
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    $\begingroup$ Hypothetical situation: suppose your table was made out of a giant block of steel that was very cold (maybe cooled in a salt+ice slurry). What happens? $\endgroup$ – chipbuster Oct 11 '16 at 1:15
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    $\begingroup$ Think about the validity of your observations in the scenario @chipbuster proposes. $\endgroup$ – bpedit Oct 11 '16 at 2:43
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    $\begingroup$ By the way: If you think you arrived at the answer you can post a self-answer here. $\endgroup$ – Jan Oct 11 '16 at 21:34
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    $\begingroup$ Our table is a phenolic resin countertop, if that gives more information. $\endgroup$ – thunderbolt Oct 13 '16 at 2:23
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You provided the additional information in the comments that your experiment was about measuring the change in temperature that occurs upon mixing. This should give you a hint as to whether the substances mix with water in an endo or exothermic manner.

When measuring temperature changes it is crucial not to influence the temperature of the reaction mixture in any way. Naturally, that would for example mean not to keep the flask in your hand (body temperature is typically more than room temperature). But some error sources are not as easily visible. In your case, the table top was an error source. Whatever the material, it likely conducts heat better than air — meaning that if your flask was on the table a significant portion of the heat generated (or used) would be conducted away (or onto site) by the table resulting in a lower change in temperature. That is why these experiments are typically performed under maximally insulating conditions. One of the best and widely available insulators is polystyrene because of its high air content (air is a good insulator). Hence, keeping polystyrene under a flask reduces the error caused by the table conducting heat.

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