Give examples of non ideal solution which show positive and negative deviation Show
Posted by Divesh Agrawal 5 years, 3 months ago
A few examples of nonideal solutions showing positive and negative deviation from Rault's law are ,
Non-Ideal Solutions: We know that a solution is made up of a solvent and a solute. The major component of a solution is the solvent (i.e. water, air), while the minor component of a solution is the solute (sugar, carbon dioxide, etc.). A concrete example would be lemonade. The water acts as the solvent, and the salt or sugar added to the water is the solute. At a given temperature and pressure, no solution is ideal and results in non-ideal solutions. A variety of forces act on non-ideal solutions, making it difficult to predict the properties of such solutions. These solutions are identified by determining the strength and specifics of the intermolecular forces between the different molecules in that particular solution. Let us explore more about non-ideal solutions in this article. Non-Ideal Solutions: Raoult’s LawIn \(1986,\) a French Chemist named Francois Marte Raoult proposed a quantitative relationship between partial pressure and the mole fraction of volatile liquids. Raoult’s law in its general form can be stated as, for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction. It is expressed by the formula: \({{\text{P}}_{{\text{solution}}}} = {{\text{X}}_{{\text{solvent}}}} \times {\text{P}}{^\circ _{{\text{solvent}}}}\) where\({{\text{P}}_{{\text{solution}}}}\) is the vapour pressure of the solution\({{\text{X}}_{{\text{solvent}}}}\) is the mole fraction of the solvent \({\text{P}}{^\circ _{{\text{solvent}}}}\) is the vapour pressure of the pure solvent In a binary solution, if a volatile solute is added to the volatile solvent, each solute’s and solvent’s component is added to the total pressure. \({{\text{P}}_{{\text{solution}}}} = \left({{{\text{X}}_{{\text{solvent}}}} \times {\text{P}}{^\circ _{{\text{solvent}}}}} \right) + \left({{{\text{X}}_{{\text{solute}}}} \times {\text{P}}{^\circ _{{\text{solute}}}}} \right)\) Raoult’s Law is akin to the ideal gas law, except as it relates to the properties of a solution. Raoult’s Law assumes ideal behaviour in which the intermolecular forces between dissimilar molecules of a solution equals forces between similar molecules. Learn Exam Concepts on Embibe Based on Raoult’s Law, liquid-liquid solutions are classified into two types of solutions, they are:
Let us look at some of the differences between ideal and non-ideal solution: What is Ideal Solution?The solutions that obey Raoult’s Law at every concentration range and at all temperatures are called Ideal Solutions.
According to Raoult’s Law, the partial vapour pressure of two components of the solution may be given as: \({{\text{P}}_{\text{A}}} = {{\text{X}}_{\text{A}}}{\text{P}}{^\circ _{\text{A}}}\) \({{\text{P}}_{\text{B}}} = {{\text{X}}_{\text{B}}}{\text{P}}{^\circ _{\text{B}}}\) Total pressure \({\text{P}}\) is given by- \({\text{P}} = {{\text{P}}_{\text{A}}} + {{\text{P}}_{\text{B}}}\) \({\text{P}} = {{\text{X}}_{\text{A}}} \times {\text{P}}{^\circ _{\text{A}}} + {{\text{X}}_{\text{B}}} \times {\text{P}}{^\circ _{\text{B}}}\) We know the total mole fraction of a solution is equal to \(1\). So, \({{\text{X}}_{\text{A}}} + {{\text{X}}_{\text{B}}} = 1\) \({{\text{X}}_{\text{A}}} = 1 – {{\text{X}}_{\text{B}}}\) Hence, total pressure \({\text{P}}\) is given by- \({\text{P}} = \left({1 – {{\text{X}}_{\text{B}}}} \right){\text{P}}{^\circ _{\text{A}}} + {{\text{X}}_{\text{B}}} \times {\text{P}}{^\circ _{\text{B}}}\) \({\text{P}} = {\text{P}}{^\circ _{\text{A}}} – {{\text{X}}_{\text{B}}}\left({{\text{P}}{^\circ _{\text{A}}} – {\text{P}}{^\circ _{\text{B}}}} \right)\) The characteristics of Ideal Solutions are as follows:
Practice Exam Questions Note: There are very few solutions that are ideal, only some solutions show ideal behaviour. Example of Ideal Solutions1. \({\text{n}}\)-hexane and \({\text{n}}\)-heptane2. Bromoethane and Chloroethane3. Benzene and Toluene 4. \({\text{CC}}{{\text{l}}_4}\) and \({\text{SiC}}{{\text{l}}_4}\) 5. Chlorobenzene and Bromobenzene6. Ethyl Bromide and Ethyl lodide7. \({\text{n}}\) – Butyl Chloride and \({\text{n}}\) – Butyl Bromide Non-ideal Solutions
Non-ideal solutions depict characteristics as follows:
Difference between ideal and non ideal solution
Attempt Mock Tests Non-ideal solutions can occur in two ways:
Positive Deviation from Raoult’s LawPositive Deviation from Raoult’s Law is observed when the vapour pressure of the components is greater than what is expected in Raoult’s Law. These solutions result when forces of attraction between dissimilar molecules \(\left({{\text{A}} – {\text{B}}} \right)\) are weaker than between similar molecules (\({\text{A-A}}\) or \({\text{B-B}}\)). The resulting solution has a larger enthalpy than its pure components , causing the process to be endothermic, i.e, heat is absorbed to make the reaction move forward. Characteristics of Non-Ideal Solution Showing Positive Deviation:In a non-ideal liquid-liquid binary solution, the vapour pressure of \({\text{A}}\) can be represented as- \({{\text{P}}_{\text{A}}} > {{\text{X}}_{\text{A}}}{\text{P}}{^\circ _{\text{A}}}\) And vapour pressure of \({\text{B}}\) can be represented as- \({{\text{P}}_{\text{B}}} > {{\text{X}}_{\text{B}}}{\text{P}}{^\circ _{\text{B}}}\) where \({\text{P}}{^\circ _{\text{A}}}\) and \({\text{P}}{^\circ _{\text{B}}}\) are respective vapour pressures in pure form. \({{\text{X}}_{\text{A}}}\) and \({{\text{X}}_{\text{B}}}\) are respective mole fractions of components \({\text{A}}\) and \({\text{B}}.\) Hence, the total vapour pressure of the non-ideal solution showing positive deviation is given by- \({\text{P}} > {{\text{X}}_{\text{A}}}{\text{P}}{^\circ _{\text{A}}} + {{\text{X}}_{\text{B}}}{\text{P}}{^\circ _{\text{B}}}\)
Example: A non-ideal solution of carbon disulphide and acetone exhibits positive deviation from Raoult’s Law. Carbon disulfide is a non-polar molecule whereas acetone is a polar molecule. As carbon disulfide is non-polar, the intermolecular forces of attraction are London dispersion forces. These forces are weak compared to other types of intermolecular forces. At the same time, acetone being polar has dipole-dipole forces, which are very strong compared to London dispersion forces. Putting these two types of intermolecular forces together in a mixture results in dipole-induced dipole interactions. But dipole-dipole induced forces are not nearly as strong as the dipole-dipole interactions between the acetone molecules. Hence, carbon disulfide-acetone solution is a non-ideal solution showing positive deviation. Few more example of non-ideal solutions showing positive deviation-
Negative Deviation from Raoult’s LawNegative Deviation from Raoult’s Law is observed when the vapour pressure of the components is less than what is expected in Raoult’s Law. These solutions result when forces of attraction between dissimilar molecules \(\left( {{\text{A}} – {\text{B}}} \right)\) are stronger than between similar molecules (\({\text{A-A}}\) or \({\text{B-B}}\)). The resulting solution has less enthalpy of solution than pure components of the solution, causing the process to be exothermic (heat is released to make the reaction move forward). Characteristics of Non-Ideal Solution Showing Negative DeviationIn a non-ideal liquid-liquid binary solution exhibiting negative deviation, the vapour pressure of \({\text{A}}\) can be represented as- \({{\text{P}}_{\text{A}}} < {{\text{X}}_{\text{A}}} \times {\text{P}}{^\circ _{\text{A}}}\) And vapour pressure of \({\text{B}}\) can be represented as- \({{\text{P}}_{\text{B}}} < {{\text{X}}_{\text{B}}} \times {\text{P}}{^\circ _{\text{B}}}\) where \({\text{P}}{^\circ _{\text{A}}}\) and \({\text{P}}{^\circ _{\text{B}}}\) are respective vapour pressures in pure form. \({{\text{X}}_{\text{A}}}\) and \({{\text{X}}_{\text{B}}}\) are respective mole fractions of components \({\text{A}}\) and \({\text{B}}\). Hence, the total vapour pressure of the non-ideal solution showing negative deviation is given by- \({\text{P}} < {{\text{X}}_{\text{A}}}{\text{P}}{^\circ _{\text{A}}} + {{\text{X}}_{\text{B}}}{\text{P}}{^\circ _{\text{B}}}\)
Example- A non-ideal solution of chloroform and acetone exhibits negative deviation from Raoult’s Law. The molecules of acetone and chloroform bond with each other through hydrogen bonding. The formation of hydrogen bonding reduces the escaping tendency of acetone-chloroform molecules. Therefore, the vapour pressure of the solution is less than that expected for an ideal solution. Few more examples of non-ideal solutions showing positive deviation-
AzeotropesBinary mixtures that have a constant composition in the liquid and vapour phase at all temperatures are called azeotropes. Azeotropes do not follow Raoult’s Law. These mixtures cannot be separated by fractional distillation. This is because the composition of the vapour phase remains the same after boiling, hence azeotropes are also known as Constant Boiling Mixtures. In these mixtures, one component has a higher or lower boiling point than the other component. There are two types of Azeotropes:
Negative Azeotrope or Maximum Boiling AzeotropeWhen two non-ideal solutions mixed at some specific composition shows a large negative deviation from Raoult’s Law results in the formation of Negative Azeotrope or Maximum Boiling Azeotrope. These mixtures have a boiling point lower than the boiling point of their constituents. Negative azeotropes have the highest vapour pressure and lowest boiling point. Examples:
Positive Azeotrope or Minimum Boiling AzeotropeWhen two non-ideal solutions mixed at some specific composition shows a large negative deviation from Raoult’s Law results in the formation of Positive Azeotrope or Maximum Boiling Azeotrope. These mixtures have a boiling point higher than the boiling point of its constituents. Positive azeotropes have the lowest vapour pressure and highest boiling point. Example:
SummaryIn this article, we learnt the different types of solutions based on Raoult’s Law. We also learnt the types of non-ideal solution and their deviation from Raoult’s Law. We also learnt the difference between Ideal and Non-ideal solutions. In this article, we also learnt about Azeotropes and its two types, i.e., Negative Azeotrope or Maximum Boiling Azeotrope and positive Azeotrope or Minimum Boiling Azeotrope FAQs About Non-Ideal SolutionsLet us look at some of the commonly asked questions about the topic: Q.1: What is a non-ideal solution with examples? Q.2: What is the ideal and non-ideal solution? Q.3: What are the types of non-ideal solutions? 2. When the intermolecular forces of attraction between dissimilar molecules are greater than those between similar molecules. This results in a negative deviation from Raoult’s Law. Q.4: What are the characteristics of a non-ideal solution? 4. The volume of mixing that is \({\Delta _{{\text{mix}}}}{\text{V}} \ne 0.\) This depicts that there will be some expansion \(({\Delta _{{\text{mix}}}}{\text{V}} > 0)\) or contraction \(({\Delta _{{\text{mix}}}}{\text{V}} < 0)\) on the dissolution of liquids. Q.5: What type of liquid form a non-ideal solution? Q.6: What makes a solution non-ideal? We hope this detailed article on Non-Ideal Solutions helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest. |