Calculating Molar Mass of Alkanes

Oct 13, 2025 by pynkocean.com 142 views

Introduction

In the world of chemistry, understanding the properties and behavior of molecules is crucial for making accurate predictions and calculations. One of the fundamental concepts in chemistry is the molar mass of a substance, which is the mass of one mole of that substance. In this article, we will delve into the concept of molar mass and explore the properties of alkanes, a type of hydrocarbon that consists of only carbon and hydrogen atoms.

What is Molar Mass?

Molar mass is a measure of the mass of one mole of a substance. It is calculated by adding up the atomic masses of all the atoms in a molecule. The atomic mass of an element is the mass of one atom of that element, and it is usually expressed in units of grams per mole (g/mol). The molar mass of a substance can be calculated using the following formula:

Molar Mass = (Number of atoms of each element x Atomic mass of each element)

For example, the molar mass of water (H2O) can be calculated as follows:

Molar Mass of water = (2 x 1 g/mol) + (1 x 16 g/mol) = 18 g/mol

What are Alkanes?

Alkanes are a type of hydrocarbon that consists of only carbon and hydrogen atoms. They are saturated hydrocarbons, meaning that they do not contain any multiple bonds between carbon atoms. Alkanes are also known as paraffins, and they are the simplest type of hydrocarbon. The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms in the molecule.

Types of Alkanes

There are several types of alkanes, including:

Methane (CH4): The simplest alkane, consisting of one carbon atom and four hydrogen atoms.
Ethane (C2H6): A two-carbon alkane, consisting of two carbon atoms and six hydrogen atoms.
Propane (C3H8): A three-carbon alkane, consisting of three carbon atoms and eight hydrogen atoms.
Butane (C4H10): A four-carbon alkane, consisting of four carbon atoms and ten hydrogen atoms.

Calculating Molar Mass of Alkanes

To calculate the molar mass of an alkane, we need to add up the atomic masses of all the atoms in the molecule. The atomic mass of carbon is 12 g/mol, and the atomic mass of hydrogen is 1 g/mol.

For example, let's calculate the molar mass of propane (C3H8):

Molar Mass of propane = (3 x 12 g/mol) + (8 x 1 g/mol) = 36 + 8 = 44 g/mol

Which of the Following is the Highest Molar Mass of a Gaseous Alkane?

Now that we have a basic understanding of molar mass and alkanes, let's answer the question posed in the problem. We are given four options for the highest molar mass of a gaseous alkane:

a) 72 g b) 44 g c) 16 g d) 30 g

To answer this question, we need to consider the possible molecular formulas of gaseous alkanes. The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms in the molecule. We can start by listing the possible molecular formulas for gaseous alkanes:

C2H6: Ethane
C3H8: Propane
C4H10: Butane
C5H12: Pentane
C6H14: Hexane

We can calculate the molar mass of each of these molecules using the formula:

Molar Mass = (Number of atoms of each element x Atomic mass of each element)

For example, let's calculate the molar mass of pentane (C5H12):

Molar Mass of pentane = (5 x 12 g/mol) + (12 x 1 g/mol) = 60 + 12 = 72 g/mol

Based on this calculation, we can see that the highest molar mass of a gaseous alkane is 72 g/mol, which corresponds to the molecular formula C5H12.

Conclusion

In conclusion, understanding the concept of molar mass and the properties of alkanes is crucial for making accurate predictions and calculations in chemistry. We have seen how to calculate the molar mass of an alkane using the formula:

Molar Mass = (Number of atoms of each element x Atomic mass of each element)

We have also seen how to apply this formula to calculate the molar mass of several gaseous alkanes. Finally, we have answered the question posed in the problem by identifying the highest molar mass of a gaseous alkane as 72 g/mol, which corresponds to the molecular formula C5H12.

The Number of Gaseous Compounds in Alkanes

Now that we have a basic understanding of molar mass and alkanes, let's answer the second question posed in the problem. We are given four options for the number of gaseous compounds in alkanes:

a) four b) five c) one d) three

To answer this question, we need to consider the possible molecular formulas of gaseous alkanes. We have already listed the possible molecular formulas for gaseous alkanes:

C2H6: Ethane
C3H8: Propane
C4H10: Butane
C5H12: Pentane
C6H14: Hexane

Based on this list, we can see that there are five possible molecular formulas for gaseous alkanes. Therefore, the correct answer is:

b) five

Conclusion

Molar Mass = (Number of atoms of each element x Atomic mass of each element)

Q1: What is the difference between molar mass and molecular weight?

A1: Molar mass and molecular weight are often used interchangeably, but technically, molar mass refers to the mass of one mole of a substance, while molecular weight refers to the mass of a single molecule. However, in most cases, the terms are used synonymously.

Q2: How do you calculate the molar mass of an alkane?

A2: To calculate the molar mass of an alkane, you need to add up the atomic masses of all the atoms in the molecule. The atomic mass of carbon is 12 g/mol, and the atomic mass of hydrogen is 1 g/mol. For example, the molar mass of propane (C3H8) is calculated as follows:

Molar Mass of propane = (3 x 12 g/mol) + (8 x 1 g/mol) = 36 + 8 = 44 g/mol

Q3: What is the general formula for alkanes?

A3: The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms in the molecule.

Q4: How many possible molecular formulas are there for gaseous alkanes?

A4: There are five possible molecular formulas for gaseous alkanes:

C2H6: Ethane
C3H8: Propane
C4H10: Butane
C5H12: Pentane
C6H14: Hexane

Q5: What is the highest molar mass of a gaseous alkane?

A5: The highest molar mass of a gaseous alkane is 72 g/mol, which corresponds to the molecular formula C5H12.

Q6: What is the difference between saturated and unsaturated hydrocarbons?

A6: Saturated hydrocarbons, also known as alkanes, do not contain any multiple bonds between carbon atoms. Unsaturated hydrocarbons, on the other hand, contain one or more multiple bonds between carbon atoms.

Q7: How do you determine the number of carbon atoms in an alkane?

A7: To determine the number of carbon atoms in an alkane, you can look at the molecular formula. The number of carbon atoms is equal to the number of carbon atoms in the formula. For example, in the formula C3H8, there are three carbon atoms.

Q8: What is the significance of the general formula CnH2n+2 for alkanes?

A8: The general formula CnH2n+2 for alkanes indicates that the number of hydrogen atoms in an alkane is always two more than the number of carbon atoms.

Q9: How do you calculate the molar mass of a mixture of alkanes?

A9: To calculate the molar mass of a mixture of alkanes, you need to calculate the molar mass of each individual alkane and then add up the molar masses of all the alkanes in the mixture.

Q10: What is the difference between a gaseous alkane and a liquid alkane?

A10: A gaseous alkane is an alkane that exists in the gaseous state at room temperature and pressure. A liquid alkane, on the other hand, is an alkane that exists in the liquid state at room temperature and pressure.

Conclusion

Molar Mass = (Number of atoms of each element x Atomic mass of each element)

We have also seen how to apply this formula to calculate the molar mass of several gaseous alkanes. Finally, we have answered the ten questions posed in the Q&A article by providing detailed explanations and examples.