How To Find Boiling Point Of a Compound: Detailed Explanations


This article discusses about the topic – how to find boiling point of a compound? We all must be knowing by now that boiling point of any substance is not directly affected by the temperature but it is the pressure that plays a vital role in deciding the boiling point of a substance.

When we consider a compound, it comprises of more than one element each having their own values of boiling points. Then how do we find the temperature at which the compound boils? Is it the average of individual boiling points or the greatest value is considered as the boiling point? Now we shall find out the answer to this question in this article. 

What do you mean by boiling point?

Boiling point of a substance or compound is that value of temperature at which the vapour pressure of the liquid/substance becomes equal in magnitude to the value of ambient pressure.

The surrounding pressure varies from place to place. For easy understanding we take the value of ambient pressure as 1 atm. At 1 atm pressure, the water boils at 100 degrees celsius, at this point the liquid  water starts getting converted into its gaseous state that is steam. Let us discuss more about boiling point in further sections.

How to find highest boiling point of a compound?

The boiling point of compound depends on many factors. If we want to find the compound with higher boiling point then we refer the following factors- 

  1. Intermolecular forces– Intermolecular forces are those forces that act between the elements of molecules. It gets difficult to boil the elements having high intermolecular forces because the forces of attraction do not let the bonds to break easily. The elements can have many types of bonds, they are ionic bond, dipole dipole interactions, Van Der Waal’s force and Hydrogen bond. The strongest bond is ionic bond weakest is the Van Der Waal’s force.
  2. Molecular weight– Larger the molecule, greater is the tendency to be polarised. And when the tendency to get polarised increases then we will require more efforts to boil the substance. The reason behind this is that attractive forces increase in magnitude when the element becomes more and more polar.
  3. Shape– If a compound has a very long chain of atoms then it will lead to a larger surface area. Due to larger surface area the Van Der Waal’s force of attraction also increases, hence the boiling point also increases. But when branches takes place, repulsive forces overpowers the forces of attraction. Hence, the boiling point decreases when branching takes place. 
how to find boiling point of a compound
Image: Boiling

Image credits: Boiling Point

How to find lowest boiling point of a compound?

We have already discussed on how to determine whether the boiling point will be high or not. We can use the same factors to find out whether the boiling point will be low or not.

The factors include intermolecular forces that are majorly of four types- Ionic bond, Van Der Waal’s force, Hydrogen bond and Dipole-Dipole. Then another factors are shape and molecular weight of the compound. In above sections we have already seen how these factors have such a strong impact on the boiling point of compounds.

How to find the boiling point of a chemical compound?

Boiling point of any chemical compound can be found using following steps. We shall consider an example in which we take a solution. The solution consists of solute and solvent. The equation that we will use is called as Clausius Clapeyron equation.

The equation is as follows-

[latex]ln(\frac{P2}{P1})= \frac{-\Delta Hvap}{R}(\frac{1}{T2}-\frac{1}{T1})[/latex]

How to find the boiling point of an organic compound?

We can find the boiling point of an organic compound by performing a simple experiment. The experiment is discussed in the section given below. We shall directly jump to the procedure part of the experiment.

  • A test tube is filled till 2/3rd height with the organic compound whose boiling point is to be determined.
  • Then using a rubber band the test tube is tied with a thermometer in such a way that the bulb of thermometer mathes the bottom of the test tube.
  • Paraffin liquid is poured in a beaker which is then kept on a hot plate.
  • The test tube along with the thermometer is dipped inside this paraffin liquid which is getting hot.
  • A capillary tube is taken whose one is sealed by heating it on a bunsen burner.
  • The open end is dipped inside the test tube.
  • We observe bubbles coming out of the open end of the capillary tube and after some time the bubbles start coming out at a higher rate. Note the temperature as t1 shown on the thermometer.
  • Now switch off the hot plate and let the paraffin liquid col down, the bubbles stop coming out from the capillary tube.
  • Now note this temperature as t2.
  • The average of t1 and t2 is the boiling point of the organic compound.

Which compound has the highest boiling point?

Ethanol or Ethyl alcohol has the highest boiling point. This is due to the high impact of van der waal force and dipole dipole interactions. These forces are a part of strong attractive forces between the molecules.

Above mentioned forces are a part of attractive intermolecular forces. These forces bind the atoms together with more grip. We need high magnitude of energy to break these bonds, hence the boiling point of the compound also becomes higher. We have discussed the effect of these factors on the boiling point.

Which organic compound has the highest boiling point?

When we talk about organic compounds, Propan-1-ol or Propanol has the highest boiling point. This is explained by the strong H bonds and OH group present in the compound.

The H bonding is also attractive in nature. Due to H bonds present inside Propanol, the energy required for boiling increases as H bonds are quite too strong and they cannot be easily broken. If the H bonds would have been weaker, then the energy required to break the bonds would have been lesser and so it could be boiled easily.

Abhishek

I, Abhishek Khambhata, have pursued Btech in Mechanical Engineering. Throughout four years of my engineering, I have designed and flown unmanned aerial vehicles. My forte is fluid mechanics and thermal engineering. My fourth year project was based on performance enhancement of unmanned aerial vehicles using solar technology. I would like to connect with like minded people.

Recent Posts