Empirical Formula of a Compound

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The aim of this experiment was to find the scientific formula for magnesium oxide. The empirical formula allows one to calculate the mole of a substance in its most basic ratio. It is important to establish the analytical formula for it allows one to differentiate it from the chemical formula of the compound of interest. However, owing to experimental mistakes, the final solution obtained could not be the correct formula for the drug. The experiment did not yield a positive result. This may have occurred as a result of incorrect measurement of the experiment parameter and improper recording of the results. It is reasonable to try as much as possible to avoid various errors so as to increase the accuracy of the results obtained.


Before commencing the experiment, a number of safety measures were observed. Magnesium ribbon is flammable and as such should be properly handled. Nitric acid is very toxic and highly corrosive. It should be handled carefully so as not to come into contact with neither skin nor eyes. Ammonia is also a very toxic and harmful gas. Any hot apparatus should be handled properly so as not to cause burns.


A compound’s empirical formula is defined as the ratio of moles of the atomic components of a compound in their simplest form. Subscript numbers indicates the ratio of these atoms in the chemical formula. It is important to know the difference between the empirical formula and chemical formula of compounds. The empirical formula may be chemical formula of a compound. However, chemical formulas of compounds do not have to be similar to the compound’s empirical formula, this is a fact that has to be clearly distinguished in experimental procedures and outcomes. For example, glucose has C6H12O6 as the chemical formula, while its empirical formula is CH2O. On the other hand, a compound such as carbon (IV) oxide has its chemical and empirical formula as CO2.

Synthesizing a chemical from its constituent elements directly is a means by which one is able to determine the empirical formula of such chemical.

There are three simple steps to be followed:

First of all, determining the mass of each element is key.

The second step is calculating number of moles found in each and every element in the compound in the sample given.

Finally, for effective empirical formula to come about, one is needed to express molar ratios of every element in the compound as whole numbers.

Looking at the example of aluminum oxide whose solid compound size was found to have 1.7grams of aluminum mass and 1.57grams of oxygen, its simple ratio obtained could be 2:3 as shown below:

Molar mass of aluminum is 26.98g Al/mol Al

1.76g Al/ 26.98g Al/mol Al = 0.0652 moles of Al

Molar mass of oxygen is 16.00g O/mol O

1.57g Oxygen/ 16.00g Oxygen/mol = 0.0981 moles of Oxygen

To obtain the ratio of the moles, divide each of the number of moles by the smallest number, which is 0.0652.

Moles ratio of Aluminum = 0.0652/0.0652 = 1.00

Mole ratio of Oxygen = 0.0981/0.0652 = 1.50

1.00: 1.50 in the simplest whole number is 2:3

This means that for every two atoms of aluminum there are three atoms of oxygen. Whether an element that is pure or a mixture like air, oxygen in its molecular form is highly reactive. However a typical component of air like nitrogen is the opposite of oxygen as it is typically and basically not reactive. The process of combustion that involves reaction of an element and oxygen leads to formation of an oxide of that element. Availability of nitrogen in the air leads to formation of nitrides of elements during combustion. Our experiment’s main course involved the combustion of a ribbon of magnesium in the air, obviously with oxygen components in them to form an oxide of magnesium or magnesium oxide compound. The empirical formula of the magnesium oxide will be determined using the initial mass of metal and the final mass of the metal oxide. In the experiment, we determined the empirical formula of the oxide of magnesium by use of the initial metal or ribbon’s mass and the final metal oxide mass obtained after the combustion.

Materials and Methods

The main materials that were used in this experiment included:

Magnesium ribbon


6M Nitric acid

Sandpaper or steel wool

Bunsen burner or a source of heat

The main method of carrying out the experiment was through combustion process. However the entire procedure of the experiment was conducted by following steps mentioned below:

Using our clean lid and crucible, we investigated for any cracks on it to ensure that everything was aright and that the general condition of the lid and the crucible was perfect for the experiment. We knew that crucible with defects could give us undesirable results. Alternatively, if our crucible were in poor condition, we ought to transfer 1 to 2 mls of HNO3 in a hood and then evaporate it and ensure it dries.

The crucible was gently heated in the source of flame for a period of 5 minutes in a gentle manner before we subjected it to an intense magnitude of flame. The crucible and its contents was continually heated for a period of ten to twelve minutes by use of the intense flame until the crucible’s bottom became red hot. The crucible was placed on a wire pad to enable it cool. We were cautious not to put the crucible on the top of the bench or touch it with our fingers considering the fact that this could be dangerous and might have led to fatalities in the laboratory.

The mass of the heated and cooled crucible and its contents including the lid was taken and measurements recorded.

The above second and third steps were done repeatedly for three rounds until reading of both the lid and the crucible did not differ by a difference above 0.010g in measurement.

A magnesium ribbon weighing approximately between 0.17 g to 0.23 g was obtained, turned into a ribbon or coil and placed inside the crucible. We cleaned any magnesium ribbons that were not shiny till they sparked. This was done to remove any formation of oxides prior to the experiment.

The clean, shiny and sparkling magnesium ribbon was placed inside the crucible and the total mass of the crucible and its contents including the lid measured and recorded.

The crucible, lid and its contents were taken back to the triangle of clay support and heated gently for two to three minutes. The heat was however intensified continuously for almost three minutes.

Crucible tongs were used to slightly lift the edges of the hot crucible in order to allow air to get I and react with the contents in the crucible, mainly the magnesium ribbon. We highly resisted removing the lid. We knew that doing this move correctly will make the metal to start glowing.

The above step was performed several times until there was no more glowing metal

Three drops of distilled water was added inside the crucible after it cooled. Smell of ammonia was felt after undertaking this step.

The crucible lit was slightly positioned off so that the evaporating water molecules could move out of the crucible during the heating process.

The crucible and its contents were allowed to co and the mass of it measured and recorded.

The crucible and its contents were again reheated for some five minutes using intensified heat. The contents were then measured after cooling and this was done until two readings that are concurrent and within 0.010g to each other was obtained.

This entire procedure was repeated using a new ribbon sample for the second trial.


First trial (Mass in grams)

Second Trial (Mass in grams)

Magnesium Ribbon



Crucible and lid – first heating



Crucible and lid- second heating



Mass of crucible lid and metal



Crucible + Lid + Metal after first heating

Crucible +Metal +Lid 2nd Heating



Mass of metal oxide

First trial: 25.6928-25.5338= 0.1598g

Molar mass of MgO = 24.315

Number of moles = 0.1598/ 24.315 = 0.0065

Second trial: 20.2528-20.0688= 0.1848g

Molar mass of MgO = 24.315

Number of moles = 0.1848/ 24.315 = 0.0076

Mass of oxygen

Trial one: 0.1598-0.1018 = 0.057g

Molar mass of oxygen = 16.00g

Number of moles = 0.057/16.00 = 0.0036

Mole ratio = (0.0063/0.0036): (0.0036/0.0036) = 1.75:1

From this, the ratio of atoms is approximately 7:4

Trial two: 0.1898- 0.1068 = 0.083g

Molar mass of oxygen = 16.00g

Number of moles = 0.036/16.00 = 0.0048

Mole ratio = (0.0076/0.0048): (0.0048/0.0048) = 1.58:1

From this, the ratio of atoms is approximately 8:5


Both first and second trials clearly indicated that the experiment did not go as expected. The results differ with the theoretical empirical formula for magnesium oxide by a great difference. This clearly indicates there were many inaccuracies and errors during the experiment. Faulty weighing apparatus may have caused some of the errors; impure reagents used, or even wrong readings. According to Unluer & Al-Tabbaa (2013), the theoretical formula for Magnesium Oxide is MgO. This implies that the ratio of magnesium and oxygen atoms in the compound should be approximately 1:1.

The empirical theoretical formula for magnesium oxide is MgO. This means that the ratio of magnesium atoms to oxygen atoms ought to be equal. This also happens to be the chemical formula for magnesium oxide.

To avoid such errors, Tang et al. (2014) advises students to ensure the reagents to be used must be pure and not contaminated by any other chemical. Also, the apparatus used must be clean as this may interfere with the preceding of the experiment. The weighing scales must be functioning properly. Experiments need to be done with a lot of concentration so as not to miss recording any detail.


The main aim of this experiment was to determine the empirical formula of magnesium oxide by heating magnesium ribbon (two trials) in a crucible. To save on time, both trials were conducted simultaneously. The actual empirical formula for magnesium oxide is MgO. According to the conducted experiment, the final ratio of magnesium to oxygen was found to be. The experiment was therefore a success.

Works cited

Tang, X., Guo, L., Chen, C., Liu, Q., Li, T., & Zhu, Y. (2014). The analysis of magnesium oxide hydration in three-phase reaction system. Journal of Solid State Chemistry, 213, 32-37. doi:10.1016/j.jssc.2014.01.036. Retrieved on February 27, 2017 from http://www.sciencedirect.com/science/article/pii/S0022459614000498

Unluer, C., & Al-Tabbaa, A. (2013). Characterization of light and heavy hydrated magnesium carbonates using thermal analysis. Journal of Thermal Analysis and Calorimetry, 115(1), 595-607. doi:10.1007/s10973-013-3300-3. Retrieved on February 27, 2017 from https://link.springer.com/article/10.1007/s10973-013-3300-3

January 05, 2023

Science Life

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