Chemistry

Factors that Affect Solubility



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Substances in different phases of matter, namely, solid, liquid, and gas, have the property to dissolve in a liquid solvent to form a homogeneous solution (Henrickson, 2005). This property is called solubility. The extent to which the mass of a substance dissolves in the solvent can be described as insoluble to highly soluble. Moreover, there are important factors that affect the solubility of substances. These factors will be discussed in the following sections.

Nature of the Solute and Solvent

A solute is a substance that can be dissolved in a given solvent, while a solvent is the substance that causes the solute to dissolve (Henrickson, 2005).  The polarity of both solute and solvent are important determinants of solubility. In view of this, the structures of substances determine their polar or non-polar characteristic. Similarities in the structures of the solute and solvent make it easier for their molecules to form a homogeneous solution. Applying the principle of ‘like dissolves like,’ solutes easily dissolve in solvents when they have the same polarity or structure (Henrickson, 2005).

In this manner, polar solutes such as ionic compounds dissolve completely in polar solvents such as water (Henrickson, 2005). Conversely, non-polar solutes dissolve better in non-polar solvents. Hence, it can be deduced from this principle that unlike solutes and solvents will not make a probable solution, which deems the solute as insoluble in the given solvent. Thus, solubility is affected by the nature of both solutes and solvents.

Temperature

The solubility of solid and liquid substances is greatly affected by temperature (Ebbing & Gammon, 2007). A high temperature causes increased solubility in these substances. Experiments have shown that ionic compounds and other substances have specific temperatures at which they become soluble in the mixed solvent. Generally, an increase in temperature makes solid substances more soluble in water.

In contrast to this, the solubility of substances in the gas phase is inversely related to the presence of a high temperature. It is very common among gas substances to dissolve less with rising temperatures. As observed, bubbles appear when liquid solutions are subjected to heat. The appearance of bubbles signals the escape of gas molecules previously dissolved in water, which means that they become less soluble in the liquid when the temperature increases (Ebbing & Gammon, 2007).

Pressure

The solubility of substances in the solid and liquid phases is not affected by pressure. However, substances in the gas phase have varied solubility when subjected to varying pressures (Ebbing & Gammon, 2007). Pressure and the solubility of gas have a direct relationship. A higher pressure leads to a higher solubility of gases (Ebbing & Gammon, 2007). This can be explained by the increased amount of gas molecules that stays in the solvent when there is a greater pressure that pushes it down in comparison to the number of molecules that leaves the solvent. Thus, it can be interpreted that there are more gas molecules dissolved in the solvent when there is higher pressure.

Imagine a bottle of soda that fizzles out once you open it. The fizzling sound is brought about by the escaping carbon dioxide molecules from the liquid. Prior to opening the soda bottle, there is a high pressure inside that keeps the carbon gas molecules mixed with the solvent. However, when the bottle is opened, the pressure becomes less and therefore the gas molecules escape, hence making them less soluble with less atmospheric pressure.

References:

Ebbing, D. D. & Gammon, S. D. (2007). General chemistry (9th ed.). MA: Cengage Learning

Henrickson, C. (2005). Cliffstudy solver. CA: John Wiley and Sons


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