Finding the Molar Mass of a Substance - The Complete Academic Support Hub

Technical Report WRITING CHENG 242 Sec. 2

Engineering Department

University of Bahrain

Finding the Molar Mass of a Substance

Sheikha Saif AlShamsi.

20191127.

Date submitted: December 19, 2020

ABSTRACT

In this report, an experiment will be conducted to calculate the molar mass. Molar mass is a quantity used to give a weigh to a substance in terms of atoms. Molar mass is also the number of protons and neutrons which is simply the mass of one mole. It can also be identified with single elements, single molecules, and other substances. So, we will how to calculate and why it’s important for us to know the atomic mass.

TABLE OF CONTENTS

1.0 Introduction 1

2.0 Theory and analysis 3

3.0 Experimental details 3

3.1 Materials 3

3.2 Procedure 3

3.3 Safety 3

4.0 Result and discussion 4

5.0 Conclusion and recommendation 5

LIST OF FIGURES

Figure 1 John Dalton 2

Figure 2 Flask 3

Figure 3 Periodic Table 4

Introduction
As humans, whenever thinking about a substance, we think how much it weighs or how much space it occupies. A substance may be small but dense which can weigh a lot and a large substance can weigh much less. In case of science, there are the small atoms that we cannot actually calculate with normal balances or units such as kg because it is not possible. So, Scientists have defined the term “mole mass”. A mole is the ratio used to convert a mass measurement to an amount of substance, where it is expressed in terms of atoms. Each mole contains 6.02*10²³ atoms, which is a lot but yet, still too small. The size of these atoms depends on the substance. The main purpose of knowing how to calculate the molar mass is that when testing specific amounts of a substance, it allows to figure how much weight of substance you have. It is also useful to analyze results of experiments. In this experiment, the molar mass of a given substance and this method can be used to most elements [1]. The experiment will be conducted using the equation:
PV=nRT
Where P=Pressure, V=Volume of the substance, n= number of moles, R=0.082, and T=Temperature in Kelvin.
The first table of atomic masses was published by John Dalton (see figure 1) and he chose hydrogen to be the standard for his table of atomic masses and gave the hydrogen atom a mass of 1.
Figure 1 John Dalton Source: “Chemist Scientists,” https://www.biography.com/scientist/john-dalton Accessed December 19, 2020.
Theory and analysis
During chemical reactions, changes in the substance involve changing the arrangement of billions of atoms. When trying to identify an amount of this substance, it is impossible to count all these atoms[2]. So, scientists need a way to identify such amount, which is molar mass and the link between atoms and molar mass is:
1 Mole of a substance = 6.02*10²³ atoms of the substance
Experimental details
Materials

Volatile liquid
Flask (as shown in figure 2)
Thermometer Figure 2 Flask Source: “Glass Erlenmeyer Flask,” www.stemcell.com Accessed December 19, 2020.
Boiling water

Procedure

Fill the flask with the vapor of volatile liquid at the temperature of the boiling water by heating the volatile liquid.
Find the mass of the vapor of the volatile liquid that filled the flask.
Find the volume occupied by the vapor of the volatile liquid (the volume of the flask) [3].
Safety
As we are dealing with volatile liquids, make sure to have:

Gloves
Googles
Lab coat

And most importantly, be careful while conducting the experiment.
Result and discussion
Because we are dealing with a gas, we should use the ideal gas law to calculate the molar mass: PV = nRT
where P is the pressure, V is the volume, T is the kelvin temperature, and R is the universal gas constant (R=0.08206) and n is the moles we also know that (m = n x MM) where m is the mass and MM is the molar mass . By these two equations we can find the molar mass directly.
MM = (mRT / PV)
And as we said before molar mass contains the weight of some atoms, so the molar mass is the sum of the atomic masses, and by the periodic table of the elements we can know their molar mass. Water is an example for a volatile liquid ( H₂O ) , and the molar mass for its elements is (H = 1 x 2 = 2 , O = 16 ) so the molar mass is equal 18 . If we do the experiment and found that the molar mass is 18 so we will end up with Hydrogen and Oxygen, which is water, which will result with the same molar mass known in the periodic table.
Figure 3 Periodic Table Source: “The Periodic Table,” http://theconversation.com/the-periodic-table-from-its-classic-design-to-use-in-popular-culture-52822 Accessed December 19, 2020
Conclusion
In the end, we defined what is molar mass and how it is important to us. The experiment was conducted and the ways of calculating the molar mass is discussed, using materials we use in our daily life. It was also discussed how to derive the molar mass of a substance using the equation PV= nRT and use the periodic table to find so. It is really important to know how to calculate the molar mass as it is considered the building block to study in the scientific field. To conclude, this experiment helped in gain a better understanding on how to find the molar mass of a particular substance.
References
[1] “Molar Mass,” https://courses.lumenlearning.com/boundless-chemistry/chapter/molar-mass/ Accessed December 2020.
[2]” Molar Mass Conversion Factors,” www.preparatorychemistry.com Accessed December 19, 2020.
[3] Abdulla Al-Mutawa, General Chemistry 1 Practical Manual. Bahrain: College of Science, 2020..