Lesson 13: Solutions

ave you ever bought a container of juice and somewhere on the container it said 100% juice from concentrate? What does that mean? When something is concentrated, all of the water is removed. A juice concentrate is much stronger than regular juice. It would be like drinking a glass of lemonade that was made without water. There would be only lemon juice and sugar. To make a juice concentrate, the water is removed, leaving only a syrup that consists of sugar and other ingredients. For preservation and easier shipping, juices are sold in their concentrated form. Once purchased by beverage bottling companies, water is added to the concentrate, and the juice is repackaged for sale to stores and consumers. In this lesson, you will learn about solutions. You will learn about different types of solutions and how they mix. You will also learn about different types of mixtures, dissolving, and solubility.
What Is a Mixture?
A mixture is a substance made by mixing materials physically. Mixtures are not chemically combined and do not undergo any sort of chemical reaction. They can usually be separated into their original parts and retain many of their own properties. Anything you can combine is a mixture. Mixtures are categorized as heterogeneous or homogeneous based on how they mix. The prefix hetero- means other or different. Aheterogeneous mixture is a mixture composed of substances that are different or not evenly mixed. In a heterogeneous mixture, you can still identify its parts. A salad is one example of a heterogeneous mixture. Even when mixed, you can distinguish all of its ingredients (the cucumbers from lettuce, cheese from tomatoes, and so on) just by looking at it. Oftentimes, a heterogeneous mixture consists of substances in different phases. For example, a glass of soda with ice is a heterogeneous mixture of ice (a solid) and soda (a liquid). heterogeneous mixture homogeneous mixture The prefix homo- means same or one. A homogeneous mixture is a mixture composed of substances that are the same throughout. The individual parts lose their identities and cannot be distinguished from each other by sight. Homogeneous mixtures have a uniform composition, appearance, and definite properties. Air is a homogeneous mixture. It is composed of different gases: hydrogen, oxygen, nitrogen, argon, water vapor, carbon dioxide, and others. Tap water is also a homogenous mixture. It is composed of water and several minerals, yet you cannot see each of the individual ingredients.
What Is a Solution?
Scuba diving is swimming underwater using special equipment. Scuba gear consists of fins for the feet, large goggles to protect the eyes, and self-contained breathing equipment called scuba diving tanks. The tanks are filled with gas and allow divers to breathe while underwater. Scuba divers wear tanks filled with a gas solution. What does scuba equipment look like? The tanks are large metal containers strapped to the diver's back. A hose extends from the top of the tank to the face. The hose connects to a mouthpiece and transports the gas from the tank to the diver, allowing him or her to breathe. The breathing gas is composed of several different gases, including air. A scuba diver would not be able to tell which gases are present in the scuba tank just by looking. The gases form a type of mixture called asolution. A solution is made up of two or more different substances combined to form a homogeneous mixture. The substances are evenly distributed throughout the mixture and cannot be separated. They are the same color, composition, density, and taste all the way through. A substance dissolves when it is mixed with another substance by breaking up into particles too small for the eyes to detect. A solution is composed of two parts: a solvent and a solute. The solvent is the substance in which another substance is dissolved. The solute is the substance that gets dissolved. In a solution, the solute cannot be separated from the solvent, not even with a filter. The substance used in the largest amount is usually the solvent. Fruit juices from concentrate are solutions in which fruit juice concentrate is the solute and water is the solvent.
Dissolving Salt dissolves by ionizing or dissociating in water. Dissolving causes a solute to mix with a solvent to form a solution. The solute particles are attracted to the solvent particles. In order for a substance to dissolve, the forces that hold the two substances together have to be conquered. There are three different ways to dissolve: dissociation, ionization, and dispersion. Dissociation is the process that occurs when an ionic compound breaks apart into its ions as it dissolves to form a solution. Sodium chloride (table salt) is an example of one such ionic compound. When mixed with water, sodium chloride separates into its ions, sodium (Na+) and chloride (Cl-). Dispersion takes place when a substance breaks apart into tiny particles and spreads throughout a liquid. When sugar is added to water, the sugar particles disperse forming a solution. Dispersion is a physical process. The particles do not react or separate into ions. They just simply spread apart. Ionization occurs when a neutral molecule gains or loses electrons while forming a solution. The compound separates into ions. The resulting solution is not neutral; it carries an electrical charge. These solutions are able to conduct electricity. Dissolving by ionization is a chemical change unlike dissociation and dispersion, which are physical changes.
Properties of Solutions There are several different types of solutions that can exist as solids, liquids, and gases in any combination. For example, water vapor is a liquid but forms a gas when in a solution with air. Salt is a solid that forms a liquid solution when combined with water. Air is a gaseous solution formed from nitrogen, oxygen, hydrogen, and other gases. Brass is a solid solution of copper and zinc. The most common solutions have liquids as the solvent. An aqueous solution is a solution in which water is the solvent. Most beverages are aqueous solutions. Soda is an aqueous solution that uses water as the solvent with carbon dioxide and sugar as the solutes, among other ingredients. Carbon dioxide and sugar dissolve in water to form soda. Many substances, when dissolved in water, form solutions that are able to conduct electricity. These substances alone are poor conductors. However, once dissolved in water they are able to dissociate or ionize. This allows the ions to move freely throughout the solution and give it an electric charge. Substances forming aqueous solutions that can conduct electricity are called electrolytes. Electrolytes dissociate, or ionize, in water. If an aqueous solution conducts electricity, the solute must be an electrolyte. Sodium chloride and hydrogen chloride are both electrolytes.
What Factors Affect Dissolving?
Remember that during a chemical reaction the particles of the reactants collide with one another. When particles collide with enough energy to overcome the activation energy, a reaction will occur. The same principle applies to solutions. When a solute and solvent come together, the particles collide and the solute dissolves. The speed at which the solute dissolves depends on the collisions. Three factors that affect the collisions and the rate at which they dissolve are surface area, temperature, and stirring.
Surface Area Dissolving takes place at the surface of a solid. Because dissolving takes place on the surface, increasing the surface area increases the rate at which a substance dissolves. When a medicine tablet dissolves in a cup of water, it dissolves from the outside first. The larger the outside of the tablet (the surface area), the more collisions are possible, and the faster the tablet will dissolve. More collisions means a faster rate of dissolving. If you break up the tablet of medicine, it dissolves even faster. Breaking the tablet increases the surface area by allowing the solvent to come in contact with more of the tablet.
Stirring If you need a medicine tablet to dissolve even faster, you could stir the mixture. Stirring speeds up the rate of dissolving. The dissolved particles are pushed away from the surface of the solid (in this case the medicine tablet) and make more room for collisions. Stirring the mixture increases the collisions between the solute and solvent. This, in turn, increases the rate at which it dissolves.
Temperature Increasing the temperature of the solvent also increases the rate of dissolving. Raising the temperature causes the solvent particles to move faster, increasing its energy. This results in even more collisions between the solvent and the solute, and the solute dissolves faster.
What Is Solubility?
Have you ever wondered why substances such as salt and sugar dissolve in water but fats such as oil do not? It has to do withsolubility. Solubility is the ability of one substance to dissolve in another. It is a physical property that measures the maximum amount of solute that can be dissolved in a specific amount of solvent. But not all solutes dissolve in all solvents. A substance capable of being dissolved is soluble. A substance that cannot be dissolved isinsoluble. Salt is soluble in water. It has a high solubility when it comes to water. Oil has a low solubility and is insoluble in water. Liquids capable of being mixed or dissolving in one another are miscible. Liquids, such as oil and water, that are incapable of being mixed with one another are immiscible. Solubility is often expressed in grams of solute per 100 grams of solvent. The more grams of solute per 100g of solvent, the more soluble the substance. The table below shows the solubility of some substances in water at room temperature (20° C). Substance   Solubility (g/100g water) at 20° C  baking soda   9.6 salt   36.0 sugar   203.9 Of the items on the chart, sugar is the most soluble, and baking soda is the least soluble.
Temperature and Pressure Tea and sugar dissolve faster in hot water. Temperature and pressure are two factors that affect solubility. Substances are likely to be more soluble at higher temperatures. The solubility of a substance generally increases as the temperature of the solvent increases. This is the reason drinks such as iced tea are made using hot water. Once the sugar has been dissolved, the tea can then be cooled or put on ice. Pressure has a similar affect on solubility. Pressure can be used to force one substance to dissolve in another. Increasing the pressure on a gas increases its solubility. Carbonated beverages consist of a gas, carbon dioxide, dissolved in a liquid. Carbon dioxide under pressure is able to dissolve in water. The pressure inside a can full of a carbonated beverage is very high. This is the reason that shaking a can of soda and opening it causes the liquid to squirt out everywhere. Polarity Water is the most common solvent and is often called the universal solvent. Why is water such a great solvent? Water is a compound with very unique properties and is able to dissolve many different substances. Water has oppositely charged poles. Water is a covalent compound that is composed of two hydrogen atoms and one oxygen atom. Its structure consists of oppositely charged poles which result in an unbalanced charge. The oxygen carries a slightly negative charge and the hydrogen atoms have a slightly positive charge. Substances that have an unbalanced charge are polar. Polarity affects solubility. Because water carries both a positive and negative charge, it is able to attract solutes with a positive or negative charge. The negatively charged poles of water are attracted to the positive parts of the solute and the positively charged poles of the water are attracted to the negative parts of the solute. Substances such as oil are immiscible in water. They do not dissolve. Oil does not dissolve in water because it is non-polar. How do you know whether two substances are soluble? Scientists use a rule, "like dissolves like", to predict solubility. Similar substances are soluble in each other. Polar substances are soluble in polar substances. Non-polar substances are soluble in other non-polar substances.
What Are the Different Types of Solutions?
Lemonade is a popular beverage during the spring and summer. The solvent is water, and the solutes are lemon juice and sugar. The type of solution that forms (for example, how sweet the lemonade is) depends on the concentration. The concentration of a solution tells how much solute has been dissolved into the solvent. The more sugar is added to the lemonade, the greater the concentration of sugar. A solution in which a lot of solute has been dissolved into the solvent is called a concentrated solution. The opposite of concentrate is dilute. A solution is diluted if it contains a small quantity of solute compared to the amount of solvent. For example, if you make a pitcher of lemonade and it is too sweet; you added too much sugar. You can dilute the lemonade by adding more of the solvent, or water. This reduces the concentration of the solution. The lemonade is not as sweet anymore because adding more solvent dilutes (weakens) or reduces the sugar concentration. There are specific terms for the concentration of a solution. Solutions can be saturated, unsaturated, or supersaturated depending on the amount of the solute in the solution and its solubility.
Saturated Solutions A saturated solution is a solution that contains as much dissolved solute as possible at a specific temperature. A solution becomes saturated when no more solute can be dissolved at that specific temperature. Any more solute added does not dissolve; it settles at the bottom of the container. It cannot dissolve because the solvent is filled with solute.
Unsaturated Solutions An unsaturated solution is a solution that has less than the maximum amount of solute. It can dissolve more solute if necessary. Most of the beverages you drink are unsaturated solutions. When making tea or lemonade, you might add sugar to make it sweeter. If all of the sugar dissolves, it is an unsaturated solution.
Supersaturated Solutions A supersaturated solution is a solution that contains more than the maximum amount of solute that can normally be dissolved in the solvent at a specific temperature. These solutions are unstable. If even the smallest amount of solute is added to a supersaturated solution, the solution will crystallize. Crystals are solids made up of particles that are neatly arranged in regular and specific repeating patterns. Rock candy is made from a supersaturated solution that turns into crystallized sugar. Remember that temperature affects solubility. The higher the temperature of the solvent, the more solute can be added and dissolved. Increasing the temperature can cause a supersaturated solution to become saturated or even unsaturated.
Think About It What happens to a saturated solution if it is heated?
What Is a Suspension? What Is a Colloid?
You have already learned about the two types of mixtures: heterogeneous and homogeneous. You have also learned that a solution is one type of mixture. This is another way to classify mixtures. Depending on the size of a mixture's particles, it might be classified as a solution, a suspension, or a colloid.
Suspensions What does a bottle of chocolate milk have in common with a bottle of Italian salad dressing? Both bottles read "shake well before using". They are both suspensions. A suspension is a heterogeneous mixture that separates into its parts over time. In a suspension, the solute particles are temporarily and unevenly mixed, forming a cloudy mixture. Particles in suspension are large and often can be seen floating around in the solvent. For example, imagine you have a clear plastic bottle filled with dirt and water. If you shake it up, the dirt mixes with the water and forms a suspension of mud. But after a while, the dirt particles settle to the bottom of the container and you are again left with dirt and water. Some suspensions last longer than others, but all will eventually settle. A very common suspension is salad dressing. Italian dressing is a suspension of oil, vinegar, and other ingredients. The ingredients temporarily mix when shaken, but after a while they settle and separate into layers. Other examples of suspensions include dust particles suspended in air, sand in water, oil in water, and peanut butter. Suspensions are responsible for the formation of substances called precipitates. Aprecipitate is a solid that forms in a solution as a result of a chemical reaction. When two liquids are mixed and a precipitate forms at the bottom of the container, the two substances have undergone a chemical reaction. The solution remaining above the precipitate is called the supernatant. Precipitates also form when a solution has been supersaturated.
Colloids Some substances do not form solutions or suspensions. They form colloids, substances that have properties of both suspensions and solutions. A colloid is made up of small particles of matter dispersed throughout a solid, liquid, or gas. Colloids are like solutions because the particles do not settle when left standing. The solute particles in a colloid are larger than those in a solution but smaller than those in a suspension. Colloids are like suspensions because they are unevenly mixed. Many common substances you deal with everyday are colloids. The table below describes the different types of colloids and gives an example of each. Types of Colloids Name What is it? Example(s) emulsion   a colloid composed of two immiscible liquids   mayonnaise, milk foam   a colloid composed of a gas trapped in a liquid or solid   whipped cream, marshmallows fog   a colloid composed of droplets of water vapor suspended in air   clouds, mist gel   a colloid composed of liquid particles trapped in a solid   butter, gelatin, cheese smoke   a colloid composed of solid and/or liquid particles trapped in air   smoke sol   a colloid composed of a solid suspended in a liquid   paint, blood           The light is scattered by the colloid on the right and passes through the solution on the left. This is called the Tyndall effect. One way to distinguish between a colloid and a suspension is to let it sit. A suspension will always settle. The solute particles of the different substances only temporarily mix with each other. Eventually, they separate into layers. Colloids can also be distinguished from solutions by sight. Remember that solutions are transparent, so they do not scatter light. The particles that make up the colloid are larger than those in a solution; they are large enough to reflect light. If you shine a light on a solution, the beam cannot be seen because the particles are too small to reflect the light. If you shine a light on a colloid, you will be able to see the light as it passes through. The scattering of light as it passes through colloids is called the Tyndall effect. The Tyndall effect gets its name from an Irish scientist named John Tyndall. He was the first person to describe the scattering of light due to colloids in the 19th century.
Making Connections
Salt accumulates on the shores of the Dead Sea. The Dead Sea is a salt lake located in the Middle East between Israel and Jordan. The Dead Sea is a gigantic salt water solution that is very concentrated. The water is about nine times as salty as the ocean. There is so much salt present that the water is unable to dissolve it all. The mineral salts precipitate and accumulate on the bottom of the sea as well as along the beaches. What is so special about the Dead Sea? First, while there is plenty of wildlife that lives in the area around the sea, the Dead Sea cannot support life. Its salt content is too high. Second, mud from the Dead Sea is thought to have healing properties. Scientists and doctors study its composition and effects as well as the climate in the area to find out why this seems to be the case. Third, people are able to actually float in the water with almost no effort. (No, the Dead Sea is not deadly to people!) A tourist demonstrates buoyancy in the Dead Sea. How is this possible? The extremely salty water has a greater density than regular water in pools, rivers, and oceans. It is so much greater that our bodies are able to float without any effort. The water pushes the body upwards, and instead of sinking, a person just bobs up and down. This is due to buoyancy, the upward force on an object produced by the surrounding fluid. This lesson introduced you to solutions. You learned about solubility, dissolving, suspensions, colloids, and different types of solutions. In the next lesson, you will learn about solutions composed of acids and bases.