-2
$\begingroup$

For my upcoming lab report, I want to look at exactly how a simple variable, such as heat or surface area, affects a reaction. But I'm having trouble finding a reaction to test this on, as my results need to have real life applications. What a few real life reactions that are easy to replicate in a school chemistry lab?

$\endgroup$
3
  • $\begingroup$ Litihum-halogen exchange at low temperature. If you don't keep you reaction temperatures below about -65C you start to get side reactions occuring that brings your yield of final product down significantly. $\endgroup$ – Waylander Sep 22 '20 at 20:15
  • $\begingroup$ The reduction of an ester to an aldehyde with one equivalent of DIBAL (diisobuylaluminum hydride) is conducted at -78oC. At higher temperature, the intermediate collapses and the aldehyde is reduced to an alcohol. Aldehyde reduction is faster than ester reduction. chemistryscore.com/reduction-aldehydes-dibal-hydride $\endgroup$ – user55119 Sep 22 '20 at 20:29
  • $\begingroup$ Do you own refrigerator? If so, why do you own this appliance? $\endgroup$ – Zhe Sep 22 '20 at 20:35
2
$\begingroup$

First, a disclaimer: there is no shortage of opinion about what comprises physical or chemical changes.

This page is entitled Identifying Physical and Chemical Changes and is intended to help instructors guide STEM students on this topic.

You might find good ideas with low overhead in the Teaching Activities section such as these, quotes from the document:

  • Heating steel wool in air and collecting the black powder that results;

  • Dissolving sugar and salt in water and comparing what happens to the electrical conductivity of the two solutions;

  • Comparing boiling water with mixing vinegar and baking soda - both produce bubbles but what's the difference?;

  • Precipitation reactions, particularly ones that produce an obvious color change, such as Epsom salts and ammonia solution; and

  • Acid - base reactions can be illustrated through the use of indicators both natural (cabbage juice) and synthetic.

These are easy and safe for the classroom and have the advantage of illustrating what are considered physical vs chemical reactions. They also have real-life analogues: adding sugar to iced or hot coffee; taking an antacid for an upset stomach; the lime that shows up in your tea kettle after a while; and so on.

You can illustrate the effect of more or less heat on the extent and rate of dissolution of a solute in a solution; or combustion of steel wool under a partial vacuum. The former isolates the heat temperature variable; the latter, percent composition of oxygen in the surroundings.

$\endgroup$
2
$\begingroup$

Try to get samples of marble (pure calcium carbonate) in a marble mason workshop. Any piece of marble will do. Or try to find samples of ordinary calcareous stone (impure calcium carbonate), that can be found everywhere along the footpaths. Check if it is made of calcium carbonate by dipping them into some vinegar : it must produce bubbles if the stone is calcium carbonate. If it's a silicate, it will not produce any bubbles. Keep the only samples that react with vineggar.

Now hit and break half of your stones with a hammer, until the stone is transformed into smaller and smaller grains, like dust or powder. When this is done, half fill two beakers or two glasses with the same amount of vineggar. Then take a handful of stones in one hand, and a handful of the obtained powder in the other hand. Throw simultaneously the stones in one beaker and the powder in the other one. You will soon observe that the reaction is much stronger with the powder, because its surface in contact with the acid is much bigger than with the stones. The reaction produces a gas which is carbon dioxide $\ce{CO2}$

Chemically speaking vinegar is a solution of acetic acid $\ce{CH3COOH}$. . The equation of the reaction is $$\ce{CaCO3 + 2 CH3COOH -> Ca(CH3COO)2 + H2O + CO2}$$If you don't like the formula of the vineggar, you can replace it by a a solution of hydrochloric acid $\ce{HCl}$ one molar. Both acids are reacting roughly the same. In that case, the equation will be easier to write : $$\ce{CaCO3 + 2 HCl -> CaCl2 + H2O + CO2}$$

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.