If you've ever wondered what maple syrup, saltwater, and the cereal-milk combo have in common, here's your answer: they’re all solutions and mixtures! While these two terms may sound alike, there are some important distinctions to keep in mind. In this article, we'll explore Solutions and Mixtures in depth.

So, what exactly is the difference between a mixture and a solution? Simply put, a mixture is when two or more substances are combined, but they don't chemically react with each other. A solution, on the other hand, is a specific type of mixture where one substance dissolves completely in another. There are different types of mixtures and solutions, each with their own unique properties. For example, a homogeneous mixture is one where the components are evenly distributed throughout, while a heterogeneous mixture has uneven distribution. Solutions can be either solid, liquid or gas, while mixtures can be any combination of these states. Finally, let's talk about pure substances. These are substances that are made up of only one type of particle, such as an element or a compound. In contrast, mixtures and solutions contain multiple particles and substances. By understanding the differences between solutions and mixtures, you can better understand the world around you and its many complex chemical interactions!

What is the difference between Mixture and Solution?

If you're studying for your AP Chemistry exam, it's important to understand the definitions of solutions and mixtures.

A solution is a homogeneous mixture where all the particles are evenly mixed. Solutions can be solids, liquids, or gases, and they are made up of a solute and a solvent. The solute is the substance that dissolves in the solvent. Solutions have uniform properties throughout the sample.

Water is known as a universal solvent because it can dissolve many substances, including ionic and polar covalent compounds. When water dissolves ionic compounds, it creates electrolyte solutions that can conduct electricity. These are called aqueous solutions.

In contrast, a mixture is a heterogeneous mixture where the particles cannot mix evenly. The properties of mixtures vary depending on their location in the mixture.

Solubility is an important concept to understand when it comes to solutions. In solids, solubility increases with temperature, while in gases, solubility decreases with temperature. Most ionic compounds with Li+, Na+, K+, NH4+, NO3- or CH3CO2- are soluble in water.

Remember, solubility refers to the maximum amount of solute that can dissolve in 100 grams of solvent at a given temperature. By understanding these basics of solutions and mixtures, you'll be well on your way to acing your AP Chemistry exam!

Types of Solutions and Mixtures

Solutions are an important part of chemistry, and they can be formed from any combination of solid, liquid, or gas. Here are some examples of solutions:

1. Saltwater: This is a solution made by dissolving salt (the solute) in water (the solvent). It is a common example of a homogeneous mixture.
2. Air: The air we breathe is a mixture of gases, including nitrogen, oxygen, and carbon dioxide. These gases are all uniformly distributed throughout the air, making it a solution.
3. Brass: Brass is an alloy made by combining copper and zinc. It is a solid solution, where the two metals are evenly distributed throughout the material.
4. Soda: Carbonated beverages like soda are solutions made by dissolving carbon dioxide gas in water. The carbon dioxide gives the soda its fizz.
5. Blood: Blood is a complex solution made up of plasma (the solvent) and various solutes like water, electrolytes, and proteins.

These are just a few examples of the many solutions that exist in our world. By understanding how solutions are formed and their properties, we can better understand the chemical reactions and processes that occur in our everyday lives.

Examples of solutions

Solutions can be categorized into different types based on their concentration levels. Dilute solutions have a low amount of solute in the solution, while concentrated solutions have a high amount of solute in the solution. Dilution is the process of adding more solvent to a fixed amount of solute, which increases the volume and decreases the concentration of the solution.

Concentrated solutions can be further divided into unsaturated, saturated, and supersaturated solutions. An unsaturated solution is a solution in which more solute can be dissolved in the solvent. A saturated solution is a solution in which no more solute can be dissolved in the solvent at a given temperature and pressure. A supersaturated solution is a solution that contains more solute than it should be able to dissolve at a given temperature and pressure. Supersaturated solutions are unstable and can crystallize or precipitate out excess solute under certain conditions. One exciting area of research in chemistry is finding efficient ways to store hydrogen gas. One approach is to dissolve hydrogen gas in metals like palladium to create a solid solution. This technique is known as interstitial hydrides. While this method is effective for hydrogen transport, it is currently expensive. Interestingly, dilute solutions of phenol (carbolic acid) were used as antiseptics in hospitals before modern disinfectants were available. Joseph Lister was a pioneer in using phenol to sterilize surgical instruments and disinfect wounds.

Unsaturated Solutions

You are absolutely right! An unsaturated solution is a solution in which the amount of solute that has been dissolved in the solvent is less than the maximum amount that can be dissolved at a given temperature and pressure. If you were to add more solute to an unsaturated solution, it would dissolve without any issues until the solution becomes saturated.

Your example of adding salt to a cup of water is a great illustration of an unsaturated solution. If you keep adding salt to the water and it continues to dissolve, you have an unsaturated solution. However, once you reach a point where no more salt can dissolve in the water, you have a saturated solution. Understanding the concept of solubility and how it affects the concentration of solutions is essential in many areas of chemistry, from drug development to environmental science.

Saturated solutions

A saturated solution is a solution in which the maximum amount of solute has been dissolved in the solvent at a given temperature and pressure. If you attempt to add more solute to a saturated solution, the excess solute will not dissolve and instead will precipitate out of the solution and settle at the bottom.

The process by which a saturated solution forms solid precipitates is called crystallization. It occurs when the rate of solute dissolving in the solvent equals the rate of solid precipitating out of the solution. Crystallization plays a significant role in various chemical processes, such as in the formation of crystals from magma and in the purification of chemicals.

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Think about a time when you added sugar to your coffee or tea, and it got to a point where the sugar stopped dissolving. This is an example of a saturated solution! If you mix two substances and they do not dissolve in one another (mixing oil and water or mixing salt and pepper), a saturated solution cannot be formed.

Supersaturated solutions

Supersaturated solutions are solutions that have a higher concentration of solute than the maximum amount that can be dissolved in the solvent at a given temperature and pressure. These solutions are created by dissolving a larger amount of solute in a solvent than is normally possible at a given temperature and pressure, followed by cooling the solution slowly. When the solution cools down, the excess solute remains in the solution, resulting in a supersaturated solution. Supersaturated solutions are usually unstable and may crystallize out when disturbed or seeded with a crystal of the solute. However, under certain conditions, such as with careful control of temperature and pressure, supersaturated solutions can be maintained for extended periods of time. Supersaturation is an essential concept in various fields, from food science to materials science.

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You are right that supersaturated solutions can be formed without heating, as in the case of honey. Honey is a supersaturated solution of sugars in water that contains more sugar than is typically possible at room temperature. Over time, the excess sugar can crystallize out of the honey, causing it to become granulated.

Heterogeneous mixtures are mixtures that contain two or more substances that are not uniformly distributed throughout the mixture. In other words, the different components of the mixture can be seen as separate phases or regions within the mixture. Examples of heterogeneous mixtures include suspensions, emulsions, and colloids. Suspensions are mixtures in which the particles of one substance are dispersed throughout another substance but settle out over time due to gravity. Examples of suspensions include muddy water and blood. Emulsions are mixtures in which small droplets of one liquid are dispersed throughout another liquid. Examples of emulsions include milk and mayonnaise. Colloids are mixtures in which very small particles of one substance are dispersed evenly throughout another substance. Examples of colloids include gelatin and fog. Heterogeneous mixtures are important in a variety of fields, from chemistry to materials science, and are often studied for their unique properties and behaviors.

Heterogeneous Mixtures

Heterogeneous mixtures are mixtures that are not uniform in composition and can be separated by physical means. Examples of heterogeneous mixtures include pizza, salad dressing, and soil. Suspensions are a type of heterogeneous mixture in which the particles of one substance are dispersed throughout another substance but settle out over time due to gravity. Like you mentioned, salad dressing is a common example of a suspension, as the oil and vinegar will separate over time.

Now, let's discuss the properties of mixtures and solutions. Mixtures can have variable composition, meaning that the amount of each substance in the mixture can vary. In contrast, solutions have a fixed composition, meaning that the amount of each substance in the solution is constant. Mixtures can also have properties that are different from the properties of their individual components. For example, a mixture of iron and sulfur has different properties than the individual elements. The mixture can be separated by physical means, and the properties of the mixture will change depending on the ratio of iron to sulfur. Solutions, on the other hand, have properties that are the same throughout the solution. The properties of a solution depend on the concentration of the solute, the type of solvent, and the temperature and pressure of the solution. Solutions can also exhibit unique properties, such as boiling point elevation and freezing point depression, which are caused by the presence of a solute in the solution.

Properties of Mixtures and Solutions

Solutions are a type of homogenous mixture consisting of particles with very small diameters that completely dissolve in the solution and cannot be seen with the naked eye. They are not capable of scattering beams of light, and they cannot be separated by filtration. Solutes are also stable at a given temperature. Mixtures, on the other hand, are heterogeneous mixtures consisting of particles that can be separated. Mixtures do not have a uniform composition and the different parts may be seen with the naked eye. Mixtures are able to scatter light.

Molarity (Molar Concentration)

We can express the composition of a solution by using molarity. Molarity is the concentration of the solute.

Molarity, which is also known as molar concentration, indicates the number of moles of a solute in 1 L of solution.

The equation for molarity is as follows:

Let's look at an example!

How many moles of MgSO4 is found in 0.15 L of a 5.00 M solution? The questions give us molarity and liters of solution. So, all we have to do is rearrange the equation and solve for moles of MgSO4.

We stated before that when more solvent is added to a sample, it becomes less concentrated (diluted). The dilution equation is:

Where,

M1 is the molarity before dilutionM2 is the molarity after dilutionV1 is the volume of solution before dilution (in L)V2is the volume of solution after dilution (in L)

Find the molarity of 0.07 L of a 4.00 M KCl solution when diluted to a volume of 0.3 L. Notice that the question gives us M1, V1, and V2. So, we need to solve for M2 using the dilution equation above.

Pure Substances Mixture and Solution

Pure water is made up of hydrogen and oxygen molecules, and it is considered a pure substance. Some examples of pure substances include Iron, NaCl (table salt), sugar (sucrose), and ethanol.

A pure substance is referred to an element or compound that has a definite composition and distinct chemical properties.

If a solution has a constant composition, then it can also be considered a type of pure substance. For example, a solution containing salt dissolved in water is a pure substance because the composition of the solution stays the same throughout.

Mixtures (heterogeneous mixtures) are not considered pure substances due to the differences in composition.

Some substances are considered a gray area in terms of whether they are pure substances or not. Substances in this category as usually those that do not have a chemical formula, like milk, air, honey, and even coffee!

After reading this, I hope that you feel more confident about the difference between solutions and mixtures, and ready to tackle any problem that comes your way!

Solutions and Mixtures - Key takeaways A solution is referred to as a homogeneous mixture composed of solute and solvent. A mixture is referred to as a heterogeneous mixture, also composed of solute and solvent. Solutions can be categorized as dilute, concentrated, unsaturated, saturated, and supersaturated. A pure substance is referred to an element or compound that has a definite composition and distinct chemical properties. Solutions can be pure substances, mixtures cannot.

References:

Brown, T. L. (2009). Chemistry: The Central Science. Pearson Education.

The Princeton Review. (2019). Cracking the AP Chemistry Exam 2020. Princeton Review.

AP Chemistry course and exam description - AP central. (n.d.). Retrieved April 29, 2022, from https://apcentral.collegeboard.org/pdf/ap-chemistry-course-and-exam-description.pdf?course=ap-chemistry

Swanson, J. W. (2020). Everything you need to Ace Chemistry in one big fat notebook. Workman Pub.

Timberlake, K. C., & Orgill, M. (2020). General, organic, and Biological Chemistry: Structures Of Life. Upper Saddle River: Pearson.

Solutions and Mixtures

What is the difference between a mixture and a solution?

A solution is a homogeneous mixture, while a mixture is a heterogeneous mixture.

What are mixtures and solutions?

Solutions are homogeneous mixtures, meaning that the solute completely dissolves in the solution/no different layers are formed. Mixtures are heterogeneous mixtures, so the solute does not mix with the solvent.

What are the types of mixtures?

Mixtures are referred to as heterogeneous mixtures or mixtures that do not have a uniform composition and separate into different regions/layers. 

How to separate mixtures and solutions?

Solution and mixtures can be separated in various ways, including evaporation, filtration, distillation, and chromatography. 

What are examples of the various types of mixtures?

Examples of mixtures include sand and water, salad dressing (oil-and-vinegar suspension), cereal in milk, and chocolate chip cookies.

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