Solubility – Definition, Types, Factors Affecting, Examples

In a solvent, a solution is a homogeneous mixture of one or more solutes. A common example of a solution is sugar cubes added to a cup of tea or coffee. Solubility is the property that allows sugar molecules to dissolve. As a result, solubility can be defined as the ability of a material (solute) to dissolve in a specific solvent.

Solubility

Solubility refers to the greatest amount of solute that can dissolve in a known quantity of solvent at a given temperature.

In a solvent, a solution is a homogeneous mixture of one or more solutes. A common example of a solution is sugar cubes added to a cup of tea or coffee. Solubility is the property that allows sugar molecules to dissolve. As a result, solubility can be defined as the ability of a material (solute) to dissolve in a specific solvent. Any substance dissolved in a solvent, whether solid, liquid, or gas, is referred to as a solute.

Product of Solubility

The phrase “solubility product” refers to salts that are only sparingly soluble. It is the maximal product of the molar concentration of the ions produced by dissociation of the molecule (raised to their proper powers).

The solubility product remains constant at a given temperature. The lower the value of the solubility product, the lower the solubility, and the higher the value of the solubility product, the greater the solubility. The elements that influence solubility vary depending on the condition of the solute:

1. Solubility of Liquids In Liquids
2. Solubility of Solids In Liquids
3. Solubility of a Gases In Liquids

• Solubility of Liquids In Liquids 

Water is referred to as a universal solvent since it dissolves practically all solutes, with the exception of a few. A substance’s solubility can be influenced by a number of circumstances.

Solubility refers to the development of a new bond between the solute and solvent molecules. Solubility is the highest concentration of solute that dissolves in a known concentration of solvent at a particular temperature in terms of quantity. Solutes are classified as highly soluble, sparingly soluble, or insoluble based on the concentration at which they dissolve in a solvent. It is stated to be soluble if a concentration of 0.1 g or more of a solute can be dissolved in a 100ml solvent. It is considered to be sparingly soluble when a concentration of less than 0.1 g is dissolved in the solvent. As a result, solubility is defined as a quantitative expression measured in grams per liter (g/L).

Different sorts of solutions can be obtained based on solubility. At a given temperature, a saturated solution is one in which a given amount of solute is entirely soluble in a solvent. A supersaturated solution, on the other hand, is one in which the solute begins to salt out or precipitate once a specific concentration is dissolved at the same temperature.

Factors affecting the solubility of a liquid in liquid:

1. Pressure: Pressure has a significantly greater impact on gases than it does on solids and liquids. When a gas’s partial pressure rises, so does the likelihood of its solubility. CO₂ is bottled under high pressure in a soda bottle, for example.
2. Temperature: People can boost a solute’s solubility characteristic by adjusting the temperature. At 20° C or 100° C, water generally dissolves solutes. Increased temperature will totally dissolve sparingly soluble solid or liquid compounds. However, in the case of a gaseous substance, temperature affects solubility in the opposite direction, meaning that as the temperature rises, gases expand and escape from their solvent.

• Solubility of Solids In Liquids 

Solid solubility has been observed to be dependent on both the composition of the solute and the solvent. People frequently see that some substances, such as sugar and common salt (NaCl), dissolve quickly in water whereas others, such as naphthalene, do not. Only polar solutes prefer to dissolve in polar solvents, while non-polar solvents dissolve only non-polar solutes, according to different observations and experimental data. As a result, one of the most important elements impacting solubility is the composition of the solvent. The discovery that like dissolves like led to the conclusion that polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes.

Let’s take a closer look at how a solid dissolves in a solvent. Dissolution occurs when a solid solute is given to a solvent and the solute particles dissolve in the solvent. The process of crystallization occurs when solute particles in a solution clash with one another and some of the particles separate from the solution.

Between these two processes, a state of dynamic equilibrium is formed, at which point the number of solute molecules entering the solution equals the number of particles exiting the solution. As a result, at a given temperature and pressure, the concentration of the solute in the solution will remain constant.

A saturated solution is one in which no more solute can dissolve in the solvent at a given temperature and pressure, and it contains the maximum amount of solute. Solubility refers to the concentration of a solute in a solution at a certain temperature and pressure. An unsaturated solution is one in which more solute can be added to the solution.

Factors affecting the Solubility of Solids In Liquids:

1. Temperature: If (∆_solH > 0), the solubility of a nearly saturated solution increases as the temperature rises, and if (∆_solH < 0), the solubility falls as the temperature rises.
2. Nature solute and solvent: Like disintegrates into like. Anthracene, for example, does not react with sodium chloride. Naphthalene and anthracene, on the other hand, dissolve quickly in benzene, whereas sodium chloride and sugar do not.
3. Effect of pressure: Changes in pressure have little effect on solid solubility. This is owing to the fact that solids and liquids are highly incompressible and are essentially unaffected by pressure fluctuations.

• Solubility of a Gases In Liquids 

The topic of gas solubility in liquids is concerned with the idea of gas dissolving in a solvent. Let’s start with a definition of solubility. Solubility is the greatest amount of solute that may be dissolved in a given solvent at a given temperature for any substance. Our current interest is the solubility of gases in liquids. The gas solubility in liquids is greatly affected by temperature and pressure as well as the nature of the solute and the solvent.

Many gases dissolve quickly in water, while others do not under typical conditions. Oxygen is only slightly soluble in water, whereas HCl or ammonia dissolves quickly.

Factors affecting the Solubility of a Gases In Liquids:

• Pressure: It has been discovered that as pressure rises, so does the solubility of a gas in liquids. Consider a system of a gas solution in a solvent in a closed container in a state of dynamic equilibrium to better understand the effect of pressure on gas solubility. Because the solution is now in equilibrium, the rate of gaseous molecules entering it is equal to the rate of gaseous molecules leaving it. Let’s say we want to raise the system’s pressure by compressing the gas molecules in the solution. The molecules of the gases will now be concentrated in a smaller volume as the pressure rises. As a result, the number of gas molecules per unit volume available above the solution will grow. Because the amount of gas molecules present above the solution has grown, the rate at which they enter the solution has increased as well. As a result, the number of gas molecules in the solution increases until a new equilibrium point is reached. As a result, the solubility of gases increases as the pressure of a gas above the solution rises.
• Temperature: With increasing temperature, gas solubility in liquids decreases. Dissolution is the process by which gas molecules in a liquid dissolve. Heat is emitted throughout the process. When a system’s equilibrium is disturbed, the system readjusts itself in such a way that the effect that caused the change in equilibrium is offset, according to Le Chatelier’s Principle. Because dissolution is an exothermic process, solubility should decrease as temperature rises, proving Le Chatelier’s Principle.

Henry’s Law

According to Henry’s law, the solubility of a gas in a liquid is directly proportional to the pressure of the gas at a fixed temperature.

“The partial pressure of the gas in the vapor phase (p) is proportional to the mole fraction of the gas (x) in the solution,” says the most popular version of Henry’s law. This is written as,

p = K_Hx

Here, K_H is the Henry’s Law constant.

Characteristics of K_H

• The type of the gas determines K_H.
• The lower the solubility of the gas in the liquid, the higher the value of K_H at a given pressure.
• As the temperature decreases, the K_H values increase, indicating that the solubility of gases increases.

Applications of Henry’s Law

• In the manufacture of carbonated drinks.
• Climbers and those who live at high altitudes will benefit from this.
• During a deep water dive.

Raoult’s Law as a special case of Henry’s Law

According to Raoult’s law,

p = x_ip_i⁰

One of the components of a gas in a liquid solution is so volatile that it exists as a gas. According to Henry’s law, it is soluble in water.

p = K_Hx

As a result, Raoult’s law is a specific case of Henry’s law, in which K_H equals p_i⁰.

Sample Problems

Question 1: What’s the point of a solubility test?

Answer:

Solubility measurements can be used to determine the size and polarity of an unknown molecule, as well as the presence of fundamental or acidic functional groups. Ionisation and, hence, a chemical reaction are required for a compound’s solubility in aqueous acid or basic.

Question 2: At 313K, benzene and toluene form perfect solutions A and B. 4 moles of toluene and 1 mole of C₆H₆ make up Solution A. Toluene and benzene are equal amounts in Solution B. In each scenario, calculate the total pressure. At 313 K, C₆H₆ and toluene have vapor pressures of 160 and 60 mm, respectively.

Answer:

A] P_M = P^‘_B + P^‘_T = (P⁰_B × X_B) + (P⁰_T × X_T)

P_M = 160 × (1/1+4) + 60 × (4/1+4)

P_M = 32 + 48

P_M = 80 mm

B] P_M = 160 × (92/170) + 60 × (78/170)

P_M = 86.588 + 27.529

P_M = 114.117 mm

Question 3: What effect does temperature have on solubility?

Answer:

For certain substances dissolved in liquid water, solubility rises with temperature. The increase in kinetic energy at higher temperatures aids the solvent molecules in more effectively breaking apart the solute molecules that are held together by intermolecular interactions.

Question 4: What is the effect of pressure on the solubility of gases in liquid.

Answer:

The solubility of gases in liquid increases as pressure rises at a certain temperature. The rate of dissolution equals the rate of evaporation if the system is in dynamic equilibrium. The quantity of gaseous particles per unit volume increases as the pressure in the system rises. As a result, more particles collide with the solution’s surface and enter it. As a result, a new equilibrium is achieved. When a result, as pressure rises, so does the solubility of gases in liquid.

Question 5: What are the effects of temperature and pressure on solubility?

Answer:

An increase in pressure and temperature contributes to higher solubility in this process. An rise in pressure causes more gas particles to enter the liquid, lowering the partial pressure. As a result, the solubility will rise.

Question 6: Heptane and octane form an ideal solution at 373 K, the vapor pressures of the pure liquids at this temperature are 105.2 kPa and 46.8 kPa respectively. If the solution contains 25g of heptane and 28.5g of octane, calculate vapor pressure exerted by heptane.

Answer:

P^oc₇H₁₆ = 105.2 kPa, P^oc₈H₁₈ = 46.8 Kpa

Mc₇H₁₆ = 100g mol^-1, Mc₈H₁₈ = 114g mol^-1

Xc₇H₁₆ = nc₇H₁₆ / nc₇H₁₆ + n₈cH₁₈ = (25/100) / ((25/100) + (28.5/114)) = 0.25/0.25 + 0.25 = 0.5

Xc₈H₁₈ = 1 – 0.5 = 0.5

Pc₇H₁₆ = 105.2 × 0.5 = 52.60 kPa

Question 7: Explain Henry’s Law.

Answer:

According to Henry’s law, the solubility of a gas in a liquid is directly proportional to the pressure of the gas at a fixed temperature.

“The partial pressure of the gas in the vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution,” says the most popular version of Henry’s law. This is written as

p = K_Hx

Here, K_H is the Henry’s Law constant.