Determination of a Chemical Formula Essay Example

to achieve a dull red glow. Once the five minutes have passed, switch off the burner. Give the crucible enough time to cool down completely, ensuring that no heat is being emitted from it when hands are cupped around it as any remaining heat could contaminate the crucible. Once cooled down, avoid touching the crucible with bare fingers and use crucible tongs instead to safely transport it to a scale.

First, weigh the crucible to the nearest 0.001g and record the mass. Then, repeat the process of heating, cooling, and weighing the crucible until the mass of the crucible and cover agrees within 0.003g between weigh-ins. Next, obtain approximately 0.3g of magnesium ribbon and place it in the crucible. Finally, reweigh the crucible and cover (including the magnesium ribbon) to the nearest 0g.

When setting up the experiment, make sure the magnesium is coiled flat at the bottom of the crucible. Place the crucible with its cover back on the ring stand, tilting the cover slightly to allow oxygen to react and create oxide. Start by gently heating it and then gradually increase the temperature. Keep heating for ten minutes using the hottest part of the flame.

Begin by turning off the Bunsen burner and allowing the crucible to cool down to room temperature. If the magnesium retains its original appearance, it indicates that it was coated with magnesium oxide. In this case, use a stirring rod to break up any leftover residue and rinse it with five drops of distilled water. The water will convert magnesium nitride (which is produced from magnesium hydroxide) into magnesium oxide when heated.

To reheat the crucible, follow these steps:
1. Reheat for

an additional 5 minutes.
2. If the residue remains any color other than gray or white, allow the crucible to cool.
3. Add 5 more drops of water and reheat.
4. Cover the crucible again and let it cool to room temperature.
5. Finally, determine the weight of the crucible to the nearest 0.

Reheat the crucible with the residue for an additional five minutes by tilting its lid. Ensure that the crucible cools down to room temperature and then weigh it again, this time to the closest 0.001g. If the masses differ by more than 0.

003 g, reheat again for the third time.

Discussions:

After heating and cooling the crucible, it was taken to a weighing station for three trials. The aim was to make sure that the mass agreed within 0. 003g each time.

The weight started at 30.43 grams and increased to 30.830 grams in the second measurement, then continued to rise slightly by an additional 0.015 grams for a total of 30.845 grams in the third measurement.

The expected result of the crucible losing moisture is a decrease in weight. It is possible that the Bunsen burner did not effectively heat the crucible due to improper adjustment or lowering of the ring stand. Placing the wire gauze on the bench may have caused residue from previous use, potentially leading to different results compared to another scale. Due to time constraints, more emphasis was placed on completing the experiment rather than ensuring proper execution. Consequently, only three weigh-ins were recorded instead of the intended fourth. The accurate measurement of the crucible's weight to the nearest 0 was done after adding 0.3g of magnesium ribbon.

001g was

recorded as 32.679g after weighing. After the weigh-in process, the crucible was heated. One noticeable observation was a faint red color seen at the bottom, though it was uncertain if the flame was in direct contact with the crucible or only with the wire triangle. Throughout the 10-minute heating period, the magnesium ribbon did not ignite.

It remained in its original shape despite being heated. There was speculation that the magnesium may have been covered in magnesium oxide. Therefore, after the crucible cooled down, an attempt was made to crush any remaining residue by removing the magnesium. Regrettably, this attempt failed as it was discovered that the magnesium was not coated with magnesium oxide. However, it should be noted that a step in the experiment, namely the crushing attempt, was omitted.

The lab procedure involved adding 5 drops of water onto the magnesium to convert magnesium nitride to magnesium hydroxide. However, this step was overlooked as we repeatedly joined other lab partner groups. Fortunately, one group we joined seemed to be following the correct procedure.

Despite forgetting the data from the first data (Nass of Crucible ; Cover), the second heating for this group was 32.828g and the third was 32.823g, which was nearly within 0.003g.
6. Supplementary Questions:
1) a) 2Mg + O2 2MgO b) 3Mg + N2 Mg3N2 c) Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3
2) a) The formula for Magnesium oxide is MgO.

The calculated formula remains consistent. However, if a crucible is not weighed at room temperature, the resulting measurement may differ. The weight of the crucible will be slightly less when hotter and slightly more when colder. Furthermore, the empirical formula uses the smallest whole number for

its subscript, while the molecular formula represents the actual number of molecules or atoms in a compound.

5) To convert 17.09 g Mg to moles, multiply by 1 mole/24.31 g Mg, which gives you 0.7030 moles Mg (4 sig fig). Similarly, the conversion of 37.3 g Al to moles can be done by multiplying by 1 mole/26.

The molar mass of Al is 26.98 g/mol, and we have 1.406 moles of Al (with 4 significant figures). In addition, the molar mass of O is 16.00 g/mol, and we possess 44.98 g of O. Thus, a ratio of 1 mole of Al to 2 moles of O can be determined.

When we divide 811 moles of O (with 4 significant figures) by the smallest value of 0.7030, we get:

• Mg: 0.7030 / 0.7030 = 1.000 mole (4 significant figures)
• Al: 1.

406 divided by 0.7030 is equal to 2.000 mol with 4 significant figures.

Oxygen: 2.811 divided by 0.

7030 = 3.999 mol (4 sig fig) Compound: MgAl2O4 = MgAl4O16. The Law of Conservation of Mass states that mass cannot be created or destroyed, but can only be changed into different forms. Therefore, in a chemical change, the total mass of reactants must equal the total mass of products. By utilizing the law of conservation of mass along with atomic and formula masses, a chemist is able to calculate the quantities of reactants and products involved in a reaction as well as determine the simplest formula for a compound.

The objective of this experiment was to replicate Antoine Lavoisier's procedures in conducting numerous combustion experiments during the 18th century. Lavoisier meticulously measured the masses of all reactants

and products involved. He calculated the combined mass of the reactants and the total mass of the products, leading him to ponder questions such as: would the reactants' mass transform into the product? In case the product had a greater mass than the reactant, what accounted for the additional mass? In this particular experiment, our aim was to chemically convert magnesium into magnesium oxide. By measuring the total mass of the reactants (Mg and O2), we determined that it equaled the total mass of the product, which is MgO.