Solutions: Non-Reactive Mixtures

Introduction

Relevance of the Topic: Chemical solutions represent the basis of experimental chemistry, being fundamental for the understanding of a series of phenomena and processes. They are homogeneous mixtures formed by at least two components: the solvent (or dispersing phase) and the solute (or dispersed phase). Knowledge about the formation, nomenclature, and calculations involving solutions is vital not only for the discipline of Chemistry but also for many other sciences and fields of study.
Contextualization: Non-reactive mixtures, i.e., those in which the solvent and solute do not chemically react with each other, are common types of solutions. Understanding them is crucial for studying biological processes, the food industry, pharmacology, biochemistry, and analytical chemistry. Such solutions are also the basis for understanding everyday phenomena, such as the salinity of seawater - which is an example of a non-reactive solution, where the solute is salt and the solvent is water.

Solvent: It is the substance that is in greater quantity in the solution and has the ability to dissolve the solute. In the case of water, which is the most common solvent, its ability to dissolve substances is tremendous - which is why it is known as the "universal solvent".
Solute: Substance that is in lesser quantity in the mixture, being dissolved by the solvent. The presence of the solute alters the physical properties of the solvent, such as its boiling point and freezing point.
Concentration: The relative amount of solute and solvent in a solution. It can be expressed in different ways, such as percentage (%), molarity (mol/L), mass/volume (g/L), or parts per million (ppm). Knowledge about the different ways to express the concentration of a solution is important for calculations involving solutions.
- Molarity: It is the most used concentration in laboratories and industries, expressed in moles of solute per liter of solution (mol/L). It is calculated by the ratio between the number of moles of solute and the volume of the solution.

Saturated Solution: A solution in which the amount of solute that has been added to the solvent is the maximum that the solvent can dissolve at a given temperature. In a saturated solution, any additional amount of solute will not be dissolved, precipitating in solid form.
Unsaturated Solution: A solution in which the amount of solute present is less than the maximum amount that the solvent could dissolve at a given temperature. In this case, the solvent still has the capacity to dissolve more solute.
Supersaturated Solution: A solution that contains an amount of solute greater than what could be dissolved by the solvent at a given temperature. The formation of a supersaturated solution requires special techniques and is an unstable process, with solute precipitation occurring from it with a simple touch or the addition of a small solute crystal.

Sea Salinity: The salinity of the sea is due to the presence of various salts dissolved in water. Seawater acts as a solvent for salt, which is the solute. As seawater is a solution, and not a mechanical mixture, salinity can vary in different regions of the ocean, depending on the amount of dissolved salt.
Saltwater vs. Brine: Saltwater is an unsaturated solution, as it can dissolve more salt. Brine, on the other hand, is a supersaturated solution, obtained through controlled evaporation techniques that allowed more salt to be dissolved than usual.

Definition of Solutions: Solutions are types of homogeneous mixtures, formed by a solvent (dispersing phase) and a solute (dispersed phase). The proportion between solvent and solute can vary, but the solvent is always in greater quantity.
Solute and Solvent: The solute is the component that is dissolved by the dispersing phase, while the solvent is the medium that will dissolve the solute. Water is a common example of a solvent, being called the "universal solvent" due to its great dissolving capacity.
Concentration of Solutions: The concentration of a solution is expressed in different ways, depending on the needs of the analysis. Molarity, mass/volume, parts per million, and percentage are some examples of concentration units.
Saturated, Unsaturated, and Supersaturated Solutions: The classification of solutions according to solute content is of utmost importance. Saturated solutions contain the maximum amount of solute that can be dissolved in a solvent at a given temperature. Unsaturated solutions can dissolve more solute. Supersaturated solutions contain more solute than theoretically could be dissolved, thus being highly unstable.

Importance of Solutions: Solutions are fundamental for the study of experimental chemistry, being widely used in laboratories and industries in chemical, biochemical, and physical processes. Understanding solutions and their properties facilitates the comprehension of various natural phenomena and processes.
Manipulation of Solutions: Knowledge about the characteristics and behavior of solutions allows for the manipulation and design of more efficient and precise experimental procedures. Moreover, it is essential for understanding everyday phenomena involving solutions, such as the salinity of the sea.

Saturated or Unsaturated Solution? A solution of 100 ml contains 30 g of solute at 25°C. If the solution has the capacity to dissolve 40 g of solute, is it saturated or unsaturated?
Calculating Molarity: In a laboratory, a student dissolves 1.25 moles of sodium chloride (NaCl) in enough water to produce 500 ml of solution. What is the molarity of the solution?
Supersaturated Solution: Describe the procedure you would follow to create a supersaturated salt solution in water. What are the important aspects to consider?