Solution (chemistry)
In chemistry, a solution is defined as a homogeneous mixture composed of a solute dissolved in a solvent. The solute is typically present in a lesser quantity compared to the solvent. For instance, in a sugar-water solution, sugar acts as the solute and water is the solvent. Solutions can exist in various states, including solids, liquids, and gases, and play a crucial role in chemical reactions, both in laboratories and natural environments.
Different types of compounds can be dissolved in solvents, primarily covalent and ionic compounds. Ionic compounds, often referred to as salts, dissociate into charged particles when dissolved in water, enabling the solution to conduct electricity. In contrast, covalent compounds, like sugar, dissolve without forming charged ions. The concentration of a solute within a solution can be manipulated by adjusting the amounts of solute or solvent, with molarity serving as a common measurement for quantifying concentration. Understanding the behavior of solutions and their constituents is essential for advancements in areas such as medicine, environmental science, and food technology.
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Solution (chemistry)
In chemistry, a solution consists of a solute that has been dissolved in a solvent. For example, in a sugar-water solution, sugar would be the solute and water would be the solvent. Generally, chemists refer to the solvent as the substance of greater quantity. In the sugar-water example, there is more water, so it is referred to as the solvent. Together, the sugar and water mix together to make a solution.
Not all solutes need to be a solid (like sugar crystals), and not all solvents need to be a liquid (like water). In carbonated soda, the solute is carbon dioxide, which is a gas, while the solvent is the actual liquid soda. If one accidentally leaves the cap off a soda bottle, one is inadvertently contributing to the separation of a solution—in this case, the carbon dioxide leaving the soda.
Background
The majority of chemical reactions, including those that take place in a laboratory and in nature, take place within a solution. Solutions do not need to exist solely as liquids; they can exist as solids and gases as well. In fact, every biological process that occurs within the human body takes place within an aqueous solution containing different chemicals and compounds. If scientists are able to better understand how different solutions work, they can develop better ways of combating illness and disease within the human body. Studying solutions can help chemists develop new ways to purify water, help foods taste better, and even freshen the air. Learning how to reverse-engineer certain substances is equally as important as knowing how to produce them, because it allows chemists to use what they have learned to produce molecular compounds that are helpful to society and to the world.
Overview
Two different types of compounds can be dissolved in a solvent: covalent compounds and ionic compounds. A covalent compound is any compound containing molecules that have been brought together through covalent bonding, in which individual atoms share their valence electrons between them. An ionic compound is any compound containing molecules that have been brought together through ionic bonding, in which when one atom gives up electrons to another, and the resulting oppositely charged ions are held together by mutual electrostatic attraction. When talking about solutions, ionic compounds are typically referred to as “salts.”
Covalent compounds and salts do not react the same way in a solution: covalent compounds dissolve in an aqueous solution, while salts dissociate. Although both compounds might appear to behave the same way when observed in a glass of water, they are undergoing dramatically different processes at a molecular level.
Sodium chloride, or table salt, is considered an ionic compound. It forms whenever a sodium atom gives up an electron, or negatively charged subatomic particle, to a chlorine atom. Because the chlorine atom has gained an extra electron, it develops a slight negative charge, while because the sodium atom is missing one of its electrons, it develops a slight positive charge. The oppositely charged ions are then held together by electrostatic attraction to form an ionic compound.
Since salt is composed of two oppositely charged ions being held together like a magnet, all that one needs to do to separate them is to add water. Water is a polar molecule, meaning that one end of the molecule behaves as though it were positively charged, while the other end behaves as though it were negatively charged. When salt is placed in water, the electrostatic pull of the water molecules causes the salt molecules to dissociate, or break apart, into their individual charged particles—in this case, a positively charged sodium ion and a negatively charged chloride ion—which then float freely in the solvent. Such solutions are called electrolyte solutions and are excellent at conducting electricity. This is why salt water makes a better conductor of electricity than water by itself.
Sucrose, a sugar, is a covalent compound. Its molecular formula is C12H22O11, meaning that one molecule of sucrose contains twelve carbon atoms, twenty-two hydrogen atoms, and eleven oxygen atoms. When sucrose is placed in water, it dissolves completely, meaning that each molecule of sucrose becomes surrounded by water molecules. Unlike in an electrolyte solution, there are no negatively or positively charge ions floating around. Understanding the differences between covalent and ionic compounds is important because it can help predict how a certain solute will react when placed in a certain solvent.
Chemists can manipulate a solution by changing the concentration of either the solute or the solvent. Adding more of either changes the properties of the solution. For instance, if one were to dissolve one teaspoon of sugar in one cup of water and five teaspoons of sugar in another cup of water, the latter cup would have a higher concentration of sugar. Each time more solute is added to a solution, the solute’s concentration increases. Likewise, the concentration of a solute can be decreased by adding more solvent.
One way to measure the concentration of a solute within a given solution is molarity. The formula for molarity is M = (moles of solute) / (liters of solution). A mole is a unit of measurement that chemists use to measure the amount of a substance. Thus, if a ten-liter solution contains ten moles of sugar, its molarity would be equal to one, as there is essentially one mole of sugar for every liter of total solution.
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