Oxidation is defined as a reaction that involves the acquisition of oxygen by a chemical substance to form an oxide. Also, chemical reactions that involve the loss of an electron are identified as oxidation reactions since the reaction leads to an increase in positively charged ions. This experiment utilizes oxidation as a process of acquiring oxygen atoms.
Most metals react with oxygen to form metal oxides in an oxidation reaction process. For magnesium, the rate of its reaction with oxygen is slow under normal conditions. When stored in the open air, magnesium undergoes oxidation, forming a deposit of its oxide on the surface. This deposit is observable from its shiny silver surface that becomes less shiny. However, this reaction can be accelerated with an increase in temperature. When combusted, magnesium quickly undergoes an oxidation reaction, forming a white oxide of magnesium. The general formula for the oxidation reaction is: Mg (s) + O (g) Mg x O z (s)
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Subscripts x and z denote the number of atoms of magnesium and oxygen respectively. In the oxidation process, parts of the magnesium react with nitrogen in the air by the equation; 3Mg (s) + N 2 (g) Mg 3 N 2 (s)
The magnesium and nitrogen compound is turned back into an oxide of magnesium by adding water (Laboratory Manual, 2014, p. 124). The following reaction curs in the conversion process; Mg 3 N 2 (s) + 3H 2 O (l) 3MgO (s) + 2NH 3 (g)
To determine the simplest formula of the oxide formed, the values of x and z must be determined. These values can be calculated when the number of moles of magnesium combusted is known, and the mass of oxygen that combines with the metal is determined. When the mole ratios of the two are calculated, the formula of the compound is determined by dividing both ratios with the smallest ratio and rounding off the figures to a whole number.
The oxidation is applicable in various industrial processes, including chemical separation of hazardous chemicals from useful products. In crude oil industries, the presence of sulfur compounds in fossil fuels has significantly been responsible for environmental pollution, such as acid rains and air pollution. One of the most efficient desulfurization processes is the oxidative desulfurization process (ODS) (Dana et al., 2019). In the first phase of ODS, sulfur-containing compounds are oxidized to form sulfoxides and sulfones. The process increases the polarity of the compounds, which are then separated from fossil fuels through solvent extraction or adsorption techniques (Dana et al., 2019). The ODS process leaves fossil fuels safer for the environment.
Procedure
A clean, dry crucible and cover were heated while placed on a clay triangle set under an iron ring and a Bunsen burner flame. The heated crucible and cover were removed with a pair of tongs, cooled, and weighed. A magnesium ribbon was scrubbed to obtain a shiny silvery piece, which was then placed in the crucible, covered, and weighed.
The crucible and magnesium ribbon were placed on the clay triangle and heated. With the tip of the blue flame touching the surface of the crucible, the heating proceeded until the bottom of the crucible turned red. The magnesium ribbon began to produce smoke and burst into a flame shortly. Immediately a flame was observed; the cover was placed on the crucible with an offset to allow the combustion process to proceed. The combustion went on until no smoke was observed. The crucible was heated for a further five minutes to ensure the combustion reaction proceeds to completion. The crucible and its contents were cooled before adding 12 drops of water to remove traces of magnesium nitride. The contents were then heated gently to remove excess water molecules and then heated strongly for another five minutes. The crucible and its contents were then cooled and weighed.
Results and Calculations
|
Mass of empty crucible + cover |
15.30 g |
|
Mass of crucible + cover + magnesium |
15.57 g |
|
Mass of crucible + cover + oxide product |
15.70 g |
Mass of magnesium
15.57-15.30 = 0.27 g
Mass of magnesium compound
15.70-15.30 = 0.40 g
Mass of oxygen in the product
0.40-0.27 = 0.13 g
Moles of Mg
Moles = mass divide by molar mass; where mass is 0.27 g and molar mass = 24.305 g
0.27/24.305 = 0.0111 moles
Moles of O
Moles = mass divide by molar mass; where mass is 0.13 g and molar mass = 15.999 g
0.13/15.999 = 0.008126 moles
The number of O moles is smaller (0.008126 moles) compared to Mg (0.0111 moles)
Mg : O = 0.0111 : 0.008126. Divide each side by the smaller number, which is 0.008126
Mg : O = 1.365 : 1
Moles of Mg rounded to a whole number
1 mole
Moles of O rounded to a whole number
1 mole
Simplest Formula
Mg 1 O 1 written as MgO
In the experiment, 0.27 g of magnesium ribbon reacted with 0.13 g of oxygen to form a compound of magnesium with a total mass of 0.40 g. Using the molar mass of magnesium (24.305) and the molar mass of atomic oxygen (15.999), the number of moles of magnesium and oxygen that react are calculated at determined as 0.0111 and 0.008126, respectively. This is then converted into a ratio of 1.365:1, indicating that 1.365 moles of magnesium in the compound combines with single atomic oxygen to form the compound. The magnesium ratio can be rounded off to a whole number, thus making MgO oxide. These results give the expected empirical formula since the burning of magnesium is theoretically expected to give MgO following the chemical equation (Rutgers School of Arts and Sciences, 2020);
2 Mg (s) + O 2 (g) → 2 MgO (s).
However, a more accurate result would have indicated a magnesium ratio closer to 1.0 that the 1.365 obtained. This indicated that some magnesium atoms did not react as expected due to insufficient reaction time or the presence of impurities.
Conclusion
Magnesium reacts with oxygen to form MgO as the simplest formula of the oxide formed. However, for a more successful experiment, heating should be done for an extended period to increase the reaction time between magnesium and oxygen. The magnesium ribbon should also be scrubbed thoroughly to eliminate impurities that interfere with the reaction.
References
Dana, M., Sobati, M. A., Shahhosseini, S., & Rahbar-kelishami, A. (2019). Separation of sulfur-containing compounds from diesel by oxidation followed by solvent extraction in a single drop column. Brazilian Journal of Chemical Engineering , 36 (3), 1343-1355. https://doi.org/10.1590/0104-6632.20190363s20180521
Laboratory Manual. (2014). Laboratory manual for General, Organic, and Biological Chemistry . Pearson Education, Inc.
Rutgers School of Arts and Sciences. (2020). Burning of magnesium . Department of Chemistry and Chemical Biology. https://chem.rutgers.edu/cldf-demos/1016-cldf-demo-burning-magnesium
