Decomposing Malachite. Purpose: To test the assumption that a chemical reaction is stoichiometric.

Variables:        Manipulated:         Mass of Malachite

                Responding:          Mass of Copper (II) oxide once Malachite has decomposed.

Controlled:         Temperature Malachite is heated to

        Time Heated (Until Malachite completely decomposes)

Method:        

Note: For safety reasons, wear a protective mask while experimenting with the decomposed copper (II) oxide as it is toxic when inhaled.

1. A varying amount of malachite is added to a dish
2. The malachite is stirred until it becomes a powder with an even composition.
3. While continuing to stir, heat the malachite on a hot plate to 200 degrees Celsius. Continue heating until the green malachite fully decomposes (indicated by the completely black colour of copper (II) oxide).
4. Measure mass of copper (II) oxide with a scale (+/- 0.01g).
5. Repeat steps 1-4 with varying amounts of malachite until a reliable amount of results are acquired.
6. Calculate the chemical of the original malachite and cooper (II) oxide.
7. Use the chemical values to plot a graph representing the relationship between the chemical amounts of malachite and copper (II) oxide.

Data collection and processing

Relationship between the chemical amount of Malachite and the amount of Copper(II) Oxide once dissolved

        

The Slope of the graph, which is also the ratio of copper (II) oxide per amount of malachite, is 2.05 (+/- 2.517%) (+/- 0.0515985), or 2.05:1.

According to the evidence, the ratio between the chemical amount of copper(II) oxide to the amount of malachite is 2.05 (+/- 0.05) : 1.

% difference =

=

= -2.5%

Conclusion and Evaluation

The ratio between malachite and copper (II) oxide (2.05 (+/- 0.05):1) is 2.5% different then the predicted value. Since the values are so close, the experiment proves that all chemical reactions are stoichiometric.

One limitation during the experiment was that the stirring rod may collect parts of malachite (or copper (II) oxide) while mixing. This may reduce the final mass of copper (II) oxide when measured, and furthermore affect the scale. This could be corrected by measuring the mass of the stirring rod with the rest of the lab equipment, and then taking the mass away to find the mass of copper (II) oxide. Another limitation is that the malachite was not completely contained while the reaction occurred, and some may have spilled out during the reaction or due to mixing. One was to contain this is to seal the malachite in a flask with a neck so it is harder for the malachite to spill out. Overall however this seemed like a fairly reliable experiment.