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Kyle Lim

Ammonium Dichromate Volcano

Untitled from Kyle]] Lim on Vimeo.

Do you remember making volcanoes when you were younger using vinegar and baking soda?
In our video, instead of making our volcano using vinegar and baking soda, we used explosively unstable ammonium dichromate
(NH4)2Cr2O7(s) . The decomposition of ammonium dichromate produces very hot solid chromium (III) oxide (this is what causes the red looking sparks in the video).

(NH4)2Cr2O7(s) à Cr2O3(s) + N2(g) + 4H2O(l)

The reaction above is a redox reaction. Redox being short for Oxidation-Reduction reaction. This describes a reaction where atoms have a change in their oxidation numbers. When an atom is "oxidized", that means it is losing an electron. When an atom is "reduced" that means it is gaining an electron. An easy way to remember what oxidizing and reducing means is through the acronym OIL-RIG. (Oxidation is loss - Reduction is gain). In our experiment, Chromium is reduced from a 6+ oxidation state, to a 3+ oxidation state, meaning it gained three electrons. Meanwhile the dichromate ions are reducing the ammonium ions into nitrogen gas and water.

Also, the reaction above is a decomposition reaction, ammonium dichromate decomposes into nitrogen gas, chromium (III) oxide and water. One way to ensure we what we have is a decomposition and not a combustion reaction is by placing a piece of wool above the reaction as it occuring. Mass it before and after the reaction has gone to completion. If you notice that the mass has increased we will be able to conclude the reaction was decomposition.

Chemical Change:
- A chemical change is when one or more of the reactants are changed into a new substance (product) where it is hard to revert back to the original reactans.

The reaction that took place in our reaction was a chemical change. Some of the signs that allowed us to come this conclusion were: the reaction produced heat, the original reactant was broken down into several smaller products (from ammonium dichromate to chromate (III) oxide, nitrogen gas and water), there was a change in oxidation state of atoms (Chromium and Ammonium), produced chromate (III) oxide which we can't revert back to ammonium dichromate.

In order to calculate the theoretical grams of products we would have had, lets assume our experiment used 100 grams of Ammonium Dichromate. The first step would be converting this to moles of Ammonium Dichromate. The molar mass of Ammonium Dichromate is 252.094 grams. You then divide 100 grams by the molar mass of Ammonium Dichromate giving you .3967 moles. Since the reaction is 1:1 ratio in regards to Ammonium Dichromate and Chromium (III) Oxide. We multiply the molar mass of Cr2O3 by moles to find how many grams of solid were produced. With a molar mass of 152 grams, 60.294 grams of Chromium (III) Oxide was produced. Nitrogen gas is also in a 1:1 ration with Ammonium Dichromate. The molar mass of N2 is 28.014g, mulitply this by .3967 moles and you get 11.11 grams of nitrogen gas produced. Now when we look at oxygen, it is in a 1:4 ratio. So we need to multiply the number of moles by 4 before mulitplying by the molar mass of water which is 18.02. This leaves us with 28.59 grams of water produced.

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