From an exhilarating cup of coffee in the morning to a relaxing chamomile tea or a glass of wine before going to bed, we come across several homogeneous mixtures in our everyday life that we call solutions. In scientific terms, a solution is a homogenous mixture of one or more solutes dissolved in a solvent. The solute is the substance that is being dissolved, while the solvent is the dissolving medium. A solute can be a gas, a liquid, or a solid. Solvents can also be gases, liquids, or solids. By convention, the solvent is usually present in a greater quantity than the solute; thus, solvent typically determines the phase of the solution. The amount of solute that has been dissolved in a given amount of solvent or solution is known as the concentration of the solution. The solution becomes saturated when the concentration of solute becomes maximum, i.e., if you add more of the solute, it will not dissolve anymore and will remain intact instead. This amount is dependent on molecular interactions between the solute and the solvent. We can mix various solutes in various solvents to get several types of solution. Let’s take a look at a few examples to get a vivid idea about solutes.
Examples of Solutes
1. Salt in Food
Salt is perhaps the most essential and widely used flavoring agent and preservative that can be found in the kitchen. Added salt enhances the positive sensory attributes of foods and even makes some otherwise unpalatable foods taste better. It is used in a variety of food products to serve several purposes such as seasoning, preservation, texture aid, fermentation control, binding agent, etc. Typically, salt is used as a solute in most of the culinary arts. Due to the presence of ionic bonds, NaCl can easily dissolve in the polar organic solvents (food items), most specifically in water. An important factor in how fast the solute will dissolve is the surface area of the solute exposed. If coarse salt is used, less surface area is exposed and it will take longer for the same amount of salt to dissolve. A finer salt allows many more ions to be exposed to water, and the solute gets diffused through the water faster. Eventually, the salt can no longer be seen by the naked eye because it is evenly distributed throughout the solution. Apart from making our food taste good, salt is also an essential micronutrient that our body requires, but the advised amount of salt intake for our body is limited to few grams per day. That’s why it is only used in minute quantities as a solute.
2. Oxygen in Seawater
Oxygen in seawater is an example of a gaseous solute dissolved in a liquid solvent. From the strangest deep sea creatures to the common coral-dwelling goldfishes, almost every aquatic animal relies on oxygen dissolved in water for living. Oxygen (solute in this case) exists as a polar molecule {O}_{2}, to which the water has a natural tendency to attract. Oxygen molecule emitted by the aquatic flora along with the oxygen from the air gets mixed with ocean waves and diffuses through the water column to reach the organisms.
3. Sugar in Tea
Have you ever added a spoon of sugar to your tea and wondered why it disappeared? When you dump a tablespoon full of sugar in the hot tea, sugar goes under a chemical process called dissolution, which results in the formation of the tea-sugar solution. The sugar, along with tea-leaves, is a solute in this case, as it is present in a lesser proportion than that of solvent (water). When we add sugar to water, the water (solvent) molecules are attracted to the sugar (solute) molecules; once the attraction becomes large enough, the water can pull individual sugar molecules from the bulk sugar crystals and forms a solution. Usually, the amount of energy it takes to break and form these bonds determines if a compound is soluble or not.
4. Quinine in Tonic Water
The tonic water has its roots in colonial India, and therefore, it is also known as the Indian Tonic water. It was originated around the early 19th century when the officials and soldiers of British India were recommended to add medicinal quinine to their diet, where it was mixed with soda and sugar to mask its bitter taste, creating tonic water. Quinine is a medication used to treat malaria and babesiosis. It is added as a solute by providing a flavor component to the tonic water and bitter lemon drink mixes. British colonials in India started mixing the tonic water with gin to make it more palatable, thus creating the gin and tonic cocktail, which is still popular today. On the soda gun behind many bars, tonic water is designated by the letter “Q” representing quinine.
5. Carbon Dioxide in Carbonated Drinks
Many of us enjoy the tangy flavor of fizzy soft drinks. The substance responsible for that tangy flavor and bubbles in the drink is carbon dioxide. More specifically, the tangy flavor is caused by the formation of carbonic acid that carbon dioxide gas (in low concentrations) produces when dissolved in water, whereas the bubbles or effervescent quality is caused by carbonation itself. The formation of carbonic acid raises the pH level of water between 3 to 4, which is approximately equal to that of apple juice and is not considered harmful. A normal human body can maintain the pH equilibrium via acid-base homeostasis. The addition of alkaline salts, such as sodium bicarbonates, potassium bicarbonates, or potassium citrate, to such drinks, can increase the ph level, and in turn affect human health.
6. Ethylene Glycol in an Antifreeze
Ethylene glycol is an organic compound with the chemical formula ({CH}_{2}{OH})_{2} that is commonly used as an anti-freezing liquid in radiators, refrigerators, and several other industrial appliances. The freezing point temperature of pure ethylene glycol is -12 °C, but when it is mixed with water, the resulting mixture freezes at even lower temperatures, and therefore, is used as an anti-freezing solution. One of the most important properties when making a glycol-water mixture is the difference in the frost protection temperature at different mixing ratios. In the case of ethylene glycol, the mixing ratios typically range between 30/70 and 35/65, depending on the required frost protection temperature.
7. Ethanol in Cocktails
The popularity of alcoholic beverages in the 21st century is quite apparent. Alcholol has been an important part of several cultures and civilizations for ages. From soft alcohols like beer and wine to hard liquors like Vodka and brandy, alcohol comes in various flavors and textures and can be found almost all around the world. Ethanol is one of the many kinds of alcohol, but it is the only one safe to be consumed by humans. Ethanol occurs in nature because of the fermentation of sugars. A cocktail is nothing but an exciting mixture of fruit juices, soda, water, and alcohol that masks the bitter tang of ethanol and makes it more palatable. Alcohol is usually present in the least amounts as a solute in the cocktails. A cocktail shaker is used to completely integrate all of the drink’s ingredients and create one elegant blend of flavors. There are various types of cocktails with some surprisingly interesting names such as Bloody mary, Angel Face, Martini, Pina-colada, Paradise, White Lady, etc.
8. Zinc in Dental Amalgam
An amalgam is an alloy of mercury with another metal. If you have ever suffered from cavities, you might have your tooth filled with dental amalgam. The most commonly used metals for making dental amalgams are silver, copper, tin, and zinc. While other metals along with mercury are present in the major concentrations, zinc is added as a solute to the mixture to prevent it from corrosion. Zinc acts as a scavenger because it prevents oxidation of the other metals in the alloy during the manufacturing process. Zinc accomplishes this by combining readily with oxygen to form zinc oxide.