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According to Encyclopedia Britannica, the law of definite proportions is a “statement that every chemical compound contains fixed and constant proportions (by weight) of its constituent elements.” Using experimental data in this investigation, it will determine the percentage composition of magnesium oxide.
Chemists believe that the energy released by the synthesis combustion reaction is sufficient to allow magnesium to also react with nitrogen in the air. This reaction produces magnesium nitride. What remains unclear is whether enough magnesium nitride forms to noticeably alter the percentage composition of magnesium oxide. This report presents the experiments procedures, results, analysis, and questions.
To find the percentage composition by mass of magnesium oxide.
What effect, if any, does the formation of magnesium nitride have on the percentage composition of magnesium oxide determined in this experiment?
The percentage composition by mass of magnesium oxide will be about 60.31% magnesium and 39.69% oxygen.
You will burn two identical strips of magnesium in ceramic crucibles.
The contents of one crucible will be analyzed as they are. In the other crucible, any magnesium nitride that may have formed will be chemically converted into magnesium oxide. You will then determine the mass of the product in both crucibles and use this value to calculate the percentage composition of magnesium oxide. You will compare the two calculated values.
1. 2. Chemical safety goggles
3. Ceramic crucible and lid
5. Ring clamp
6. Bunsen burner clamped to the retort stand
7. Clay triangle
9. Dropper bottle containing distilled water
10. One 8cm strip of magnesium ribbon
11. Spark lighter
The materials were selected and brought to the station. Safety protocol was followed and safety glasses were worn throughout the experiment. The appropriate data tables were drawn in which to record the data observations.
Part A: Not Correcting for Magnesium Nitride
The mass of a clean, dry crucible and lid were measured on a scale and recorded. A single strip of magnesium was coiled and placed at the bottom of the crucible. The mass of the crucible was measured and recorded again, but with the magnesium ribbon inside. A ring clamp was attached to a retort stand and was adjusted so that the flame of the Bunsen burner touched the bottom of the crucible. The clay triangle was put on top of the ring clamp and the crucible was secured in the centre of the triangle. The lid was left slightly ajar. Using tongs, it was necessary to practice covering and uncovering the lid from the crucible. This helped to avoid any mishaps during the experiment. The burner was lit until the flame was clean blue and the magnesium in the crucible was heated gently. The lid was lifted approximately every minute to observe the reaction. The magnesium was heated until it no longer flared, then the burner was turned off. The crucible was removed and put aside to cool. The mass of the crucible and contents were weighed and recorded, then left for Part B.
Part B: Correcting for Magnesium Nitride
Using tongs, the cooled crucible was transferred to the bench top. The white ash was crushed with a stirring rod (amendment: because the procedure for Part B was missing; the white ash was not crushed). Enough distilled water to cover the contents was added to the crucible. It was heated once again for about two minutes in order to evaporate the water, then again for 5 minutes to convert any magnesium nitride into magnesium oxide. The burner was turned off; the crucible was removed from the clamp and was left to cool. The mass of the contents and the crucible were weighed and recorded. The contents were discarded of by professor’s instruction and the workstation was cleaned.
Mass of crucible and lid
Mass of crucible, lid and Mg
After heating (first time)
After adding H2O
After heating (final time)
This lab was conducted in order to confirm the chemical formula of magnesium oxide. In this investigation, one strip of magnesium was coiled and put into a ceramic crucible and cooked over a Bunsen burner with an intense flame. The magnesium nitride that may have formed was chemically converted to magnesium oxide and the mass and percentage composition of the product was determined.
Source(s) of Error
This investigation required extreme caution as there were many possibilities for error. In order to prevent magnesium oxide escaping from the crucible during heating, the lid was left slightly ajar. The size of the slot (too large) could have greatly altered the final mass of the product. Magnesium may not have reacted completely with oxygen. The water may not have evaporated completely. Any leftover compounds in the crucible from previous experiments may have varied or contaminated the reaction. Leftover compounds could also have added extra mass to the total mass. The water could have been contaminated. Also, the weighing scale could have been faulted.
Part B of this investigation was lacking and this caused confusion with the procedure. For future classes, Part B should be added. Also, the Apply & Extend questions should be clearer as they were quite confusing.
By carefully applying heat and oxygen to a strip of pure magnesium, it was demonstrated that magnesium oxide was formed. The theoretical percentage composition of magnesium in magnesium oxide is 60.31%, although the actual percentage composition was 61.76%. The hypothesis was deemed unsuccessful. The actual composition was similar, but not the same as the theoretical composition and this could have been the result of multiple instrumental or human errors.
1. Identify the major variables that you measured and or controlled in this investigation. Was there a causal relationship between any of the variables? Explain.
1. The major variables in this investigation are the magnesium and heat. The controlled variables were the position of the crucible lid, the intensity of the heat and the amount of time the magnesium was cooked. The relationship between the variables was the properties of an element that causes them to react.
1. List your sources of error in this experiment. Identify one error that could significantly affect your results. What effect would it have? How could you correct for this error?
1. For a list of sources of error see Source(s) of Error. An error that could have significantly altered the results would be to not place the crucible lid so that it was slightly ajar. This could have affected the formation of the magnesium oxide by not allowing enough oxygen to pass. This could have easily been corrected by moving the lid so that it was slightly open.
1. Calculate the theoretical percentage composition of magnesium oxide, MgO.
1. Determine the mass of oxygen that reacted with magnesium in Part A and in Part B.
The mass of oxygen did not change.
1. Calculate the percentage composition of magnesium oxide using your experimental data from Part A.
The percentage composition of magnesium is 61.76% and the percentage composition of oxygen is 38.24%.
1. Calculate the percentage composition of magnesium oxide using your experimental data from Part B.
The mass of the magnesium oxide in Part B remained the same, therefore the percentage composition also remained the same.
1. Compare the three different values for percentage composition of magnesium oxide. Try to explain any differences.
1. The percentage composition of magnesium oxide did not change from Part A to Part B, as it maintained a mass of 32.47g, even after being mixed with water and heated again. The actual experimental percentage compositions were slightly different than that of the theoretical ones because there were possible instrumental or human errors.
1. Answer the Testable Question that was posed at the beginning of this investigation. Support your answer with evidence.
1. The testable question that asked: what effect, if any, does the formation of magnesium nitride have on the percentage composition of magnesium oxide determined in this experiment? The formation of magnesium nitride has a significant impact on the percentage composition of magnesium oxide. There is only 60.31% of magnesium in magnesium oxide. If there is more magnesium nitride in the mixture, then the percentage of magnesium will also be higher.
1. A student observes unreacted magnesium remaining in the crucible. What effect would this have on the percentage composition calculation? Why?
1. The unreacted magnesium remaining in the crucible would affect the percentage composition calculation by making it lower, because not all of the magnesium was used up in the reaction.
1. Suggest a modification of this experiment that would prevent magnesium from reacting with nitrogen.
1. By lifting the lid of the crucible regularly, it could have prevented the magnesium from reacting with nitrogen, and instead it will allow adequate supplies of oxygen from the air to react. The magnesium will react preferentially with oxygen, but if all the oxygen is used up, the magnesium will react with the nitrogen.
1. Research and write the chemical reactions involved in converting magnesium nitride to magnesium oxide during Part A of this experiment.
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