Factors Affecting Solubility

Introduction

Factors affecting solubility are mentioned below as follows −

• Solutes: The substance which is added to the solvent to dissolve into it.

• Solvents: The liquid part or major volume part which absorbs the solute particles when added to it.

• Insoluble: If some stones or sand are added into water and tried to mix it, these solute particles are not dissolved into water hence, the solute (stone or sand) is insoluble in solvent water.

• Soluble: If a tablespoon of honey or sugar is added into water and tried to mix it, it completely dissolve into water and hence, the solute (honey or sugar) is soluble in solvent water.

• Sparingly soluble: If some substance like, oil or salts like silver chloride $\mathrm{(AgCl_3)}$ are added and mixed into water, it get dissolve in very small amount hence, the solute (oil or $\mathrm{AgCl_3}$) is sparingly soluble in solvent water.

Figure 1: Comparative soluble, sparingly soluble, and insoluble compounds in solvent

ZabMilenko: orginal ZooFari: vector Mrmw: optimized, multilang, Chemical precipitation diagram multilang, CC0 1.0

Factors Affecting Solubility

There are three main factors affects solubility of substance are as follows −

• Temperature (affects solid and gases)

• Pressure (affects only gases)

• Surface area (rate of solubility)

Temperature a factor which affects solubility of Solids and Gases

Temperature mainly effects on the solubility of solid and gas compounds and there is no predictions mentioned on liquid solubility. Temperature effect on solubility of solid compound which depend on the reaction i.e. an exothermic or endothermic. To explain this Le-Chatelier’s principle prescribed some postulates −

Exothermic reaction (ΔH is negative or less than zero)

Temperature rise creates strain on reactant part due to extra heat applied. Le-Chatelier principle suggests that equilibrium shifts left (reactant side) increases the reactants and decreases the solubility of solid compounds.

Endothermic reaction (ΔH is positive or greater than zero)

Temperature rise creates strain on product side due to application of extra heat. Le-Chatelier principle suggests that equilibrium shifts right (product side) increases the products and increases the solubility of solid compounds.

Temperature can directly affect the solubility of substances. For ionic solid compounds, solubility increases with increase in temperature. With increase in temperature the solid particles dissolve fast in the solution, due to which the solute particles are more interacted with solvent particles hence, the solubility rate increases. With increasing temperature more quantity of solute particles is miscible in solvent i.e. more particles of solute are miscible at high temperatures.

If salt is added into water it gets readily soluble in water. But if we apply external heat to that solution, more quantity of salt is added to water. This happens because the intermolecular forces between solvent molecules increases as well as hydrogen bonds (in case of water solvent) get easily breaks with increasing temperature and the salt (solute) particles are accompanied in between the spaces of solvent molecules.

In case of gaseous compounds, solubility decreases with temperature rise. With rise in temperature, the gas molecules moves fast and hence get evaporated from liquid solvent. Thus, gaseous compounds solubility decreases with increase in temperature.

Pressure which affects Solubility of Gases

Pressure generally affects the solubility of gaseous compounds in liquid solvent and not for solid compounds. When external pressure is applied on gaseous substance on solvents surface, the gaseous particles are immersed and occupied some space into the liquid solvent. For instance, carbonated soda (Coca cola), external pressure is applied on carbon dioxide gas molecules to enter into the soda can. If the pressure of gas decreases, gas solubility also decreases. As we open the soda can the, pressure get decreases and the $\mathrm{CO_2}$ gas instantly leaves the solution and comes out of the can.

Solubility of gas pressure is prescribed in Henry’s Law states that, at given temperature, the solubility of gas in liquid solvent is proportional to its partial pressure of gas in liquid. For instance, Scuba diving, in a deep sea when person dives, more gases are soluble in blood with the rise of pressure at underwater and when person comes out of the sea all the soluble gases slowly releases out from blood.

Surface area a factor which affects Solubility Rate

The bigger the size or surface area of solute its solubility rate is low while small size or surface area of solute its solubility rate is high. For instance, sugar with large surface area or particles, it takes more time to dissolve into water, while salt or sugar with small surface area or particles takes less time to dissolve into water. Thus, the molecules with big surface area soluble for longer time while the molecules with fine particles can soluble quickly.

For instance the copper (II) sulphate has various forms like crystalline form with large crystals and fine amorphous powder form. If we take same amount of both form of copper (II) sulphate i.e. 5g to dissolve in 50mL of solvent water. The crystalline form of copper (II) sulphate takes more time to dissolve in water even it needs stirring and shaking for some time. While the fine amorphous form of copper (II) sulphate can get dissolve in very less time with few seconds of stirring. Thus, the particle size or surface area of solute affects the rate of solubility with different time.

Conclusion

There are three basic factors affects solubility i.e. temperature, pressure, and surface area of solutes. Temperature affects only solid and gaseous compounds. With the rise in temperature solubility of solids increases while rise in temperature results in a decrease in solubility of gases.

By applying external pressure on any solvent surface the gaseous solute get interacts with solvent particles and dissolved into the solvent. Surface area factor affects the rate of solubility of solute into solvent. Solute with large surface area takes more time to dissolve into solvent while solute with small surface area takes less time to dissolve into solvent.

FAQs

Q1. What are solutes?

Ans. Solutes are solid, liquid or gaseous substances added to solvent.

Q2. Which factors affects solubility?

Ans. Temperature, pressure and surface area are the factors affecting solubility of solid- liquid, liquid-liquid or gas-liquid solutions.

Q3. What happen when external temperature applied on solid solutes and liquid solvents?

Ans. When temperature applied to solid solute mixed with liquid solvent, the solubility of solid solute increases in solution.

Q4. What happen when external temperature applied on gaseous solutes and liquid solvents?

Ans. When temperature applied to gaseous solute mixed with liquid solvent, the solubility of gaseous solute decreases in solution.

Q5. How the pressure affects the solubility of gaseous solutes?

Ans. When pressure applied on solvent surface the intermolecular forces breaks and the gaseous particles get interacts with them and get dissolved into solvent.

Q6. What is the effect of surface area of solutes on solubility?

Ans. Bigger the surface area of solute decreases the rate of solubility. Lesser the surface area of solute, increase the solubility rate.