Factors Affecting Solubility

Solubility is the process or property of a matter (Solid, liquid, or gas) which helps them dissolve in another matter called solvent (Solid, liquid, or gas). Therefore, a matter is called soluble if it dissolves in a solvent. For instance, take a small amount of salt and dissolve it in water. Here, salt is known as a solute, and water is a solvent to make a solution of saltwater. Therefore, you can say salt is soluble in water and solubility is the property of salt (or solute). 

Further, there are several factors affecting solubility depending upon which state this solute is in. Read on to know more about the various factors which affect the solubility property of solutes present in various states. 

Factors Affecting Solubility of Substances 

Here, the solvent is taken as a liquid, and the solute will be taken for all three states to help you understand these factors that affect solubility. 

• Liquid as solvent. 

• Solids as solvent. 

• Gases as solvent. 

Read further to learn in detail about the 3 factors that affect solubility. 

1. Liquid as Solvent

Solubility is the property of a solvent which can be described as the bond formation between a solvent and solute. In other words, you can describe solubility as the maximum solute concentration, which is to be dissolved in this given value of solvent concentration at a known temperature. 

Based Upon this Property, Any Solvent can be Categorized into Three Types – 

1. Highly Soluble Substance: If 0.1 g of solute is capable of dissolving in a 100g of solvent, then it falls into the highly soluble category.  

2. Sparingly or Partially Soluble Substance: If less than 0.1 g of solute is capable of dissolving in a 100g of solvent, then it falls into the sparingly soluble category.  

3. Insoluble: Understandably, this solute cannot be dissolved into a solvent. 

While this proves solubility as a quantitative expression, there are several factors affecting the solubility.  

Three Factors that Affect Solubility 

Chemical and physical properties of the solute affect its solubility. Here are some significant factors which affect the solubility property. 

1. Pressure 

It affects solutes in their gaseous state more than the ones in a solid or liquid state. The solubility property of a gas is said to increase with the increase in partial pressure of the gas. You can think of a soda bottle as an example. Here, carbon-di-oxide is bottled under a condition of high pressure. 

2. Temperature 

Water is called the universal solvent and can dissolve most of the solutes at a temperature of 200C or 1000C. In the case of sparingly soluble substances which are liquid, the solubility increases with upsurge in temperature. In the case of gases, the solubility declines with a rise in temperature of the solvent. 

3. Bonds and Forces 

The bonds and forces between these molecules of solute are one of the factors affecting solubility. Since the kind of bonds and intermolecular forces between two substances vary, the solute is known to be more soluble if it is dissolved in a likewise solvent. For instance, you can dissolve Ethanol (a polar solute) easily into a polar solvent such as water.

2. Solids as Solvent

It is seen that if the solute is a similar kind to that of solvent, it is soluble in nature. For instance, you can easily dissolve salt, sugar, or ethanol in the water where all these are polar solute and solvent. However, it is rather challenging to dissolve a nonpolar solute like naphthalene into water. 

Crystallization – When you add a solid solute into a given concentration of this liquid solvent, the particles (solid) get dissolved in the solution. This process is termed as dissolution. Crystallisation occurs when the particles of solute collide with the particles present in solution, and some of it separates from the solution.

Subsequently, a dynamic equilibrium state will be achieved when the number of solute molecules entering a solution becomes equal to the number of molecules leaving it. Further, there can be a situation wherein you cannot add more solute to the solution as it will not be dissolved. In such a case, you have reached saturation, and the solution is known as a saturated solution. 

Therefore, solubility can be defined as the solute concentration present in this solution at saturation for a known value of temperature and pressure. Further addition of solute in this solution turns it into an unsaturated solution with extra undissolved solute. 

Factors that can Affect Solubility

1. Pressure

Since solids are highly incompressible in nature and small changes in pressure have nearly no impact on it, solubility factors like pressure do not cause many changes. 

2. Temperature 

As per Le Chatelier’s Principle, the solubility of a solvent should increase if the process of dissolution is endothermic. On the contrary, solubility decreases if this dissolution process turns out to be exothermic.

3. Gases as Solvent

If Gases as a solute needs to be dissolved in a solvent, there are factors influencing solubility, such as temperature, nature of solvent and solute, and pressure. There can be several gas solutes which can readily dissolve in solvent whereas few gas solutes which do not dissolve under normal conditions. 

For instance, you can easily dissolve ammonia or HCl into the water, but oxygen acts as a sparingly soluble substance for water. 

Factors Affecting Solubility of Substances

1. Temperature

As there is a rise in temperature, the solubility of a gas solute in liquids must increase. This can be inferred from Le Chatelier's Principle. As per this principle, the system readjusts itself whenever a state of equilibrium is disturbed. 

Now, gas molecules are dissolved in liquid with the help of the dissolution process, which is an exothermic process. In an exothermic process, heat is evolved, which causes a change in the equilibrium state. Therefore, to readjust the system and validate the principle of Le Chateliers, increase in temperature of the solution should decrease the solubility. Hence, temperature is one of the 4 factors that affect solubility.

2. Pressure 

As per the experiments and observation, the pressure increase is likely to cause an increase in solubility of gases. To better understand the things that affect solubility (In this case, Pressure), consider a closed cylinder in a dynamic equilibrium state with gas as solute and liquid as a solvent. Therefore, the number of molecules entering a solution must be equal to the number of molecules leaving that solution at dynamic equilibrium state. 

Now consider increasing the amount of pressure applied to the system. This results in compressing gas molecules of this solution, which causes them to concentrate in a small volume. 

Therefore, with the increase in pressure, this concentration of gas molecules present per unit volume above the solution is increased. Resultantly, this rate with which the number of molecules enters the solution will also increase. Consequently, this number of gas (solute) molecules in a solution will also increase unless the solution undergoes into a new dynamic equilibrium state. 

Hence, you can infer that pressure increment of this solute can cause an increase in the solubility of solutes or gases. So, pressure is one of the factors that affect the rate of solubility significantly. 

Henry’s Law – 

According to Henry’s law, the solubility of solute or gas in a liquid solvent is proportional to the pressure applied to the gas above the liquid solution’s surface. 

It provides the quantitative relation between solubility of gas and pressure of gas as expressed in the equation below – 

P = KHX 

Where, 

• P is the partial pressure of solute /gas. 

• KH is Henry’s law constant. 

• X indicates the mole fraction of gas in a liquid solution. 

These are a few factors affecting the solubility of substances. You can increase or decrease factors like pressure, temperature, bonds, and forces to increase or decrease the solubility rate of elements. 

Reading this, you will be able to cover which factors affect solubility and how it affects the entire process of dissolution. For a comprehensive approach, you can download Vedantu’s app and refer to the study material there. Learn the intricacies of the chapter with quality notes prepared by professional tutors and improve your academic score.

Surface Area and Its Effect on the Rate of Dissolving

One other factor to understand is how the rate of solubility is affected by the surface area factor. If the surface area of a solid has to be increased the solid has to be cut into smaller sections which would help in speeding up the solute's dissolution in the solution. When a bulk of sugar is dissolved in water, the sugar cube crystal dissolves more slowly than the equal number of microscopic sugar crystals present in the solution. As the surface area of all the sugar crystals present is much bigger than that of a single sugar cube, therefore the sugar crystals will have more contact with the water molecules. This is the main reason why the sugar crystals dissolve more significantly faster.

When working in a lab,  sometimes it is requested to prepare a copper(II) sulfate solution. Where Copper(II) sulfate comes in a variety of shapes and sizes, including big blue crystals and small blue crystals. When equal amounts of both forms are put in the test tubes which are filled with 10 mL of water, it is observed that after 5 minutes, the fine crystals have dissolved more (and the solution becomes darker blue) than the large crystals present in another test tube. These can be alternatively split into tiny crystals into two different test tubes by taking two samples. By placing the cork on one of the test tubes and gently shaking it while the other test tube remains still at this time. Shaking increases the number of fine crystals that come into touch with the water and therefore we see an increase or increment in the surface area. The outcome remains the same as before also the test tube with the greater surface area will dissolve far more quickly. Although increasing surface area allows for faster attainment of maximum solubility, the concentration of the solute at maximum solubility remains constant.

Effect of Physical Changes on Solubility

The physical and chemical changes also affect the solubility very highly. A physical change occurs when a substance's composition stays unchanged despite its molecules being rearranged. Physical change is only a blip on the radar. For instance, ice melting, etc.

Few properties of physical changes are as follows:

1. The physical change is a temporary change.

2. The production of energy is not usually involved in physical changes.

3. Original substance used can be generally recovered which means that physical change is easily reversible.

4. There is no new substance formed in physical changes.

5. Absorption of energy is almost null or zero in the case of physical changes.

6. It only affects the physical properties of the substance such as the shape, size, etc.