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Lesson 2.1 Homogeneous and Heterogeneous Mixtures Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It! 3 Mixtures...

Lesson 2.1 Homogeneous and Heterogeneous Mixtures Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It! 3 Mixtures 3 Classifying Mixtures 4 Homogeneous Mixtures 5 Heterogeneous Mixtures 5 Solutions: Homogeneous Mixtures 6 Types of Solutions 7 Suspensions and Colloids: Heterogeneous Mixtures 8 Suspensions 8 Colloids 9 The Tyndall Effect 12 Key Points 14 Check Your Understanding 14 Challenge Yourself 16 Bibliography 17 Unit 2: Separating Mixtures Lesson 2.1 Homogeneous and Heterogeneous Mixtures Introduction A cup of coffee, a bottle of wine, and a puddle of mud have something in common. These are all examples of mixtures. A cup of coffee contains water, coffee extract, sugar, and sometimes milk. Wine is made up of alcohol and water, the products of fermentation. A puddle of mud is composed of dirt, water, and possibly other substances. Mixtures are a classification of matter which is made up of two or more pure substances that can have varying compositions. In this lesson, you will learn about the different classifications of mixtures. 2.1. Homogeneous and Heterogeneous Mixtures 1 Unit 2: Separating Mixtures Learning Objectives DepEd Competency Differentiate between In this lesson, you should be able to do the homogeneous and heterogeneous following: mixtures Differentiate between homogeneous (STEM_GC11MP-Ia-b-8). and heterogeneous mixtures. Identify mixtures as solutions. Identify mixtures as suspensions and colloids. Warm Up Mixing It Up! 15 minutes In this activity, you will observe properties of some common mixtures. Materials graduated cylinder, 50 mL beakers, 100 mL stirring rod flashlight rock salt sand water milk Procedure 1. Prepare three beakers and label them as A, B, and C. 2. Fill beakers A and B with 100 mL of water. Fill beaker C with 100 mL of milk. 3. Add a pinch of rock salt to beaker A. Stir and record your observation in Table 2.1.1. 4. Add a pinch of sand to beaker B. Stir and record your observation in Table 2.1.1. 5. Stir the contents of beaker C vigorously, and record your observation in Table 2.1.1. 2.1. Homogeneous and Heterogeneous Mixtures 2 Unit 2: Separating Mixtures 6. Perform the flashlight test to each beaker. Place the flashlight on the side of the beaker and turn it on. Observe if the light shines through the beaker, seeing it on the other end. Record your observations in Table 2.1.1. 7. Answer the guide questions that follow. Observation Table Table 2.1.1. Observations on some examples of mixtures Flashlight Test Beaker Observations (Does the light pass through or not?) A B C Guide Questions 1. What happened after dissolving rock salt in water? How many phases do you see? 2. What happened after mixing sand and water? How many phases do you see? 3. How many phases do you see in milk? 4. Which of the mixtures allowed the light from the flashlight to pass through it directly? Learn about It! Mixtures As you recall from the previous unit, there are two classifications for matter based on composition and properties—a pure substance or a mixture. A pure substance cannot be further broken down or purified by physical means. Each substance has its own characteristic properties that are different from the set of properties of any other substance. On the other hand, mixtures are combinations of two or more pure substances in which each substance retains its own composition and properties. In this lesson, you will learn more about how mixtures are made, and what the different types of mixtures are. 2.1. Homogeneous and Heterogeneous Mixtures 3 Unit 2: Separating Mixtures Classifying Mixtures Almost every sample of matter that we ordinarily encounter every day is a mixture. The combined substances in mixtures can be mixed in varied proportions. In a mixture, substances do not react with each other. For example, take a mixture of salt and pepper. Salt and pepper are physically mixed together, but they do not combine chemically to form a new substance with new properties. Each component in the salt and pepper mixture retains its original properties. The salt remains salty, while pepper remains spicy. Also, we can make an infinite number of different mixtures of salt and pepper by varying the relative amounts of the two components used. Fig. 2.1.1. When salt and pepper are combined together, a mixture is formed. Since the components of a mixture are combined physically, the components can be easily separated by physical means as well. In order to separate the two components in the salt and pepper mixture in Fig. 2.1.1, you could treat it with water to dissolve the salt, collect the pepper by filtration, and then evaporate the water to obtain the salt in solid form. The techniques illustrated are some examples of separation techniques that can be employed in mixtures. Other ways of separating mixtures include sieving, decantation, distillation, and chromatography, to name a few. These techniques will be further discussed in the succeeding lessons. Remember In any mixture, the composition can be varied, and each component of the mixture retains its own properties. 2.1. Homogeneous and Heterogeneous Mixtures 4 Unit 2: Separating Mixtures A mixture can be classified based on the distribution of the components. It can be classified as a homogeneous mixture or a heterogeneous mixture. How can you differentiate between homogeneous and heterogeneous mixtures? Homogeneous Mixtures A homogeneous mixture is a type of mixture that has uniform composition and properties. The components of a homogeneous mixture are spread out evenly all throughout. It has only one phase; thus, the components cannot be distinguished from each other. Homogeneous mixtures are also called solutions. Shown below are some examples of homogeneous mixtures that you may encounter in your daily life. fruit juice coins soda Fig. 2.1.2. Some examples of homogeneous mixtures Other examples of solutions include saltwater; some alloys, which are homogeneous mixtures of metals in the solid-state; and air (free of particulate matter or mists). Air is a mixture of gases. It is mainly nitrogen, oxygen, argon, carbon dioxide, water vapor, and some trace amounts of other substances in the atmosphere. Heterogeneous Mixtures The second type of mixture has components distinguishable from one another, with each portion having recognizably different properties. Such a mixture, which is not uniform 2.1. Homogeneous and Heterogeneous Mixtures 5 Unit 2: Separating Mixtures throughout, is called a heterogeneous mixture. A heterogeneous mixture has varying composition and properties. It may have two or more phases, and the individual substances are visually distinct. Shown below are some examples of heterogeneous mixtures that you may encounter in your daily life. candies oil and water soup Fig. 2.1.3. Some examples of heterogeneous mixtures Other examples of heterogeneous mixtures include mixtures of salt and pepper (in which two components with different colors can be distinguished easily from each other by sight), foggy air (which includes a suspended mist of water droplets), and vegetable soup. Solutions: Homogeneous Mixtures Homogeneous mixtures are also called solutions. In a solution, one component is uniformly dissolved and scattered in another component to form a homogeneous composition. It consists of two components: the solvent and the solute. Regardless of the states of the pure substances mixed together, the solvent is the one that is more abundant in solutions. It is the dissolving medium. The solute is the component present in less amount in a solution. It is the substance being dissolved. When a solute dissolves in a solvent, the solute particles break apart into very small pieces and get evenly distributed in the bulk of the solution. This results in a mixture having a consistent appearance and composition all throughout. The particles of a solution are too small to be seen by the naked eye and to be distinguished from each other. 2.1. Homogeneous and Heterogeneous Mixtures 6 Unit 2: Separating Mixtures Consider brine as an example of a homogeneous mixture. Its components are salt and water. In this mixture, salt is the solute and water is the solvent. Once you dissolve the salt in water and stir it vigorously, a brine solution is prepared. This liquid mixture has a uniform appearance. Remember Homogeneous mixtures are mixtures whose components are evenly distributed and cannot be distinguished from one another. They are also called solutions. Types of Solutions Solutions may be classified based on the physical state of the solvent—namely, solid, liquid, and gaseous solutions. Liquid solutions are solutions wherein the solvent is in the liquid phase. It is the most common type of solution. It could be a solid-liquid solution, liquid-liquid solution, or a gas-liquid solution. Seawater is an example of a liquid solution. Salts of calcium and sodium are the solutes, while water is the solvent. Listed in the table below are some examples of liquid solutions. Table 2.1.2. Some examples of liquid solutions Type of Solution Solution Solute Solvent solid-liquid saltwater salt water liquid-liquid vinegar acetic acid water gas-liquid carbonated drinks carbon dioxide water Solid solutions are solutions wherein the solvent is in the solid phase. For example, alloys are solid solutions because they are made up of metal mixed together with another metal. Listed in the table below are some examples of solid solutions. 2.1. Homogeneous and Heterogeneous Mixtures 7 Unit 2: Separating Mixtures Table 2.1.3. Some examples of solid solutions. Type of Solution Solution Solute Solvent solid-solid brass zinc copper liquid-solid amalgam mercury silver Gaseous solutions are solutions wherein the solvent is in the gaseous phase. Air is an example of a gaseous solution. When it is free of particulate matter or mist, the air is a mixture of gases composed of several gases like oxygen, argon, carbon dioxide, water vapor, and some trace amounts of other substances that are all dissolved in nitrogen gas, the most abundant gas component in the atmosphere. Suspensions and Colloids: Heterogeneous Mixtures Recall that heterogeneous mixtures are mixtures whose composition and appearance is not consistent all throughout. The components of a heterogeneous mixture are visually distinct from each other. It can have two or more phases. Heterogeneous mixtures can be further classified based on the distribution of its components. There are two types, namely suspensions and colloids. How can you determine the type of heterogeneous mixture? Suspensions A suspension is a type of heterogeneous mixture in which the solute particles do not dissolve, but get suspended throughout the bulk of the solvent when left undisturbed. The solutes form clumps or layers that do not easily break into smaller pieces. A separate, distinct layer from the solvent will be formed when the solute settles due to gravity. The separate layer is usually seen at the bottom of the container. Particles of a suspension are larger than particles of a solution. 2.1. Homogeneous and Heterogeneous Mixtures 8 Unit 2: Separating Mixtures Sand in water is an example of a suspension. When sand is mixed with water, it will initially look like a hazy mixture. But after some time, the sand will settle at the bottom of the container. It forms two distinct layers of sand and water. Fig. 2.1.4. Sand in water is an example of a suspension. Other examples of suspensions include mud (soil suspended in water), dust (solid soot and ash particles suspended in air), and vegetable soup (vegetable suspended in water). Colloids A colloid is a heterogeneous mixture in which a microscopically dispersed substance, insoluble or soluble particles, is suspended throughout another substance. A colloid is made up of a dispersed phase (solute-like particles) and a dispersing medium (solvent-like medium). The dispersing medium can be regarded as a homogeneous mixture. Unlike suspensions, colloids usually do not separate into layers or clumps. Its components may separate, but it will take a very long time to do so. In addition to this, the dispersed phase particles are very light and minute enough to stay suspended in the dispersing medium for a long time, unlike the large particles that settle in suspensions. Colloids can be considered as in between the homogeneous nature of solutions and the heterogeneous nature of suspensions. Like solutions, colloids appear as though they have a uniform composition. But unlike solutions, their particles are larger and are not evenly distributed throughout the bulk of the dispersing medium. In terms of particle size of the dispersed phase particles, colloids have larger particles than solutions but smaller particles than suspensions. Colloids, like solutions, can be classified based on the physical state of the dispersing medium. They can be classified either as gaseous colloids, liquid colloids, or solid colloids. 2.1. Homogeneous and Heterogeneous Mixtures 9 Unit 2: Separating Mixtures Gaseous colloids are colloids having the dispersing medium in the gaseous phase. The dispersed phase particle can either be a solid or a liquid. A solid aerosol is formed when the dispersed phase is a solid. An example of a solid aerosol is smoke. Smoke contains solid particulate matter or very small particles that are dispersed in the air. A liquid aerosol is formed when the dispersed phase is a liquid. Deodorant spray is an example of a liquid aerosol, where the liquid deodorant solution is suspended in the air when it is sprayed. Liquid colloids are colloids having the dispersing medium in the liquid phase. A solid, gas, or another liquid can act as the dispersed phase. A solid disperse phase suspended in a liquid is called a liquid sol. An example of liquid sol is ink. The solid, insoluble pigments are suspended in a liquid organic solvent in ink. On the other hand, a liquid suspended in another liquid is called an emulsion. Milk is an example of an emulsion as liquid fats and proteins are dispersed in water. Finally, a gas suspended in a liquid is called a liquid foam. One example is shaving foam. Air is dispersed in the liquid soap medium to form the foamy texture in shaving foam. Lastly, solid colloids are colloids having the dispersing medium in the solid phase. A gas, liquid, or another solid can act as the dispersed phase. A gas dispersed in a solid is called a solid foam. Styrofoam is an example because gas is suspended in a solid polymer matrix of polystyrene. On the other hand, a liquid suspended in a solid is called a gel. An example of a gel is Jell-O. Liquid water molecules are dispersed in a solid gelatin matrix. Finally, a solid suspended in another solid is called a solid sol. Colored glass is an example of a solid sol because insoluble solid pigments are suspended in the solid matrix of the glass. Listed in the table below are some examples of colloids and their corresponding types. The observable difference between solution, suspension, and colloid is the solute’s particle size. In a solution, its particles are very small that they cannot be seen by the naked eye. The solute particles are evenly distributed in the solvent. In a suspension, the particles are very large that they can be distinguished by the naked eye. These particles are insoluble. Initially, suspensions may appear homogeneous. But after some time, the particles of a suspension settle down, making it heterogeneous. Intermediate to the particle sizes of solutions and suspensions are that of colloids. Although the particles in a colloid may appear to be evenly distributed, the particles are not totally dissolved, and they do not settle after some time. 2.1. Homogeneous and Heterogeneous Mixtures 10 Unit 2: Separating Mixtures Table 2.1.4. Some examples of colloids Physical State Examples Name Dispersing Dispersed Dispersed Dispersing Mixture Medium Phase Phase Medium gas solid solid aerosol smoke solid air particulates gas liquid liquid perfume liquid air aerosol sprays perfume solution liquid gas liquid foam shaving air shaving foam solution liquid liquid emulsion milk fat water liquid solid liquid sol ink Solid Water, pigments organic solvents solid gas Solid foam styrofoam air polystyrene solid liquid gel gelatin water gelatin mix solid solid solid sol colored glass solid glass pigments Remember Heterogeneous mixtures are mixtures of two or more phases combined together with varying composition and properties. A heterogeneous mixture can be classified either as a suspension or colloid. 2.1. Homogeneous and Heterogeneous Mixtures 11 Unit 2: Separating Mixtures How can you differentiate solutions, suspensions, and colloids? The Tyndall Effect One way to differentiate colloids from solutions and suspensions is by Tyndall effect. Colloidal particles exhibit Brownian motion and cause the Tyndall effect. Brownian motion is the random movement of particles suspended in gas or liquid. This random movement of particles causes the scattering of light or the Tyndall effect. It is usually demonstrated by passing a ray of light through a sample mixture. Through this test, the mixture could be easily identified as a solution, suspension, or colloid. Fig. 2.1.5. The Tyndall effect When light passes through a given mixture, the mixture is a solution. Light will have a narrow path and is not clearly visible. Since solutions have the smallest particle size which the naked eye cannot see, light is not blocked by the particles of a solution. When light does not pass through a given mixture, the mixture is a suspension. Since suspensions have the largest particle size, light is blocked by the particles of a suspension. Suspensions appear opaque. 2.1. Homogeneous and Heterogeneous Mixtures 12 Unit 2: Separating Mixtures When light passes through a given mixture and the light scatters, the mixture is a colloid. Colloids have an intermediate particle size. Due to its intermediate particle size, some light can pass through, and some are blocked and scattered. Unlike a suspension, colloids are not necessarily opaque. Among the three, only colloids exhibit the Tyndall effect. For example, milk is a colloid composed of fat and proteins suspended in water. It appears homogeneous since the suspended fat particles are too small. However, these particles are too big to be evenly distributed like solutes in solutions. Therefore, these colloidal particles scatter light. Tips When differentiating between homogeneous and heterogeneous mixtures, you should first look for uniformity. If the mixture has only one phase, it is a homogeneous mixture (solution). If it has two or more phases, it is a heterogeneous mixture. Colloids may appear homogeneous; hence, it is better to check if colloidal particles are present by passing a ray of light through the mixture. If the light scatters, the mixture is a colloid. If the light passes through, the mixture is a solution. To check if the mixture is a suspension, let it sit for some time and observe if large particles will settle at the bottom. Did You Know? The Tyndall effect is named after the 19th century physicist, John Tyndall. In his investigations on radiant heat in the air, it was necessary for him to use air from which all traces of floating dust and other particulates had been removed. In order to detect particulates, the most sensitive way is to bathe the air with intense light. The scattering of light by particulate impurities in the air and other gases, and in liquids, is known today as the Tyndall effect or Tyndall scattering. 2.1. Homogeneous and Heterogeneous Mixtures 13 Unit 2: Separating Mixtures Which between a chocolate drink, a glass of salt water, and mudwater would scatter a beam of light from a flashlight? Key Points ___________________________________________________________________________________________ A mixture is a blend of two or more substances combined together through a physical process. A homogeneous mixture is a combination of two or more substances that cannot be distinguished from each other. It has uniform composition and properties. A heterogeneous mixture is a combination of two or more substances that can be distinguished from each other. It has varying composition and properties. Homogeneous mixtures are also called solutions. A suspension is a heterogeneous mixture whose solutes do not completely dissolve. The insoluble particles settle into clumps or layers when left undisturbed. A colloid is a heterogeneous mixture whose solute-like particles are dispersed in a medium. ___________________________________________________________________________________________ Check Your Understanding A. Identify the term(s) described in each of the following items. ___________________________ 1. It is the mixture that has a constant appearance all throughout. ___________________________ 2. It is the mixture that has varying composition and properties with two or more component substances with different phases. 2.1. Homogeneous and Heterogeneous Mixtures 14 Unit 2: Separating Mixtures ___________________________ 3. It is the mixture whose solutes are insoluble in the medium, forming layers or clumps that settle when left undisturbed. ___________________________ 4. It is a mixture made up of two components: the solute and the solvent. ___________________________ 5. It is the scattering of light that is caused by the random motion of particles suspended or dispersed in a medium. B. Classify the given mixture if it is homogeneous or heterogeneous. ___________________________ 1. instant coffee ___________________________ 2. milk ___________________________ 3. soy sauce ___________________________ 4. perfume ___________________________ 5. bronze ___________________________ 6. beef noodle soup ___________________________ 7. muddy water ___________________________ 8. steel ___________________________ 9. mouthwash __________________________ 10. smog C. Complete the table below by classifying the given mixtures as a solution, suspension, or colloid. Identify the phases of the solute (dispersed phase) and the solvent (dispersing medium) as well. 2.1. Homogeneous and Heterogeneous Mixtures 15 Unit 2: Separating Mixtures Phase Mixture Classification Solute (or Solvent (or Dispersed Phase) Dispersing Medium) 1. rubbing alcohol 2. whipped cream 3. chalk in water 4. vinegar 5. fog Challenge Yourself A. Answer the following questions. 1. Gladys wants to make a cup of hot tea. She dipped a tea bag into a cup of hot water and noticed that the color of the liquid changed as the tea and hot water mixed together. a. What type of mixture did Gladys prepare? Explain your answer. Then, Gladys decided to open the tea bag and pour the contents into the same cup. b. What type of mixture did Gladys prepare now? Explain your answer. c. What should Gladys do to make the new mixture have the same properties as the first mixture she prepared? 2. After using the restroom, you washed your hands in the sink. You pumped the liquid soap dispenser only to find out that instead of liquid, foam was supplied. a. What type of heterogeneous mixture did you observe? b. How will you describe the soap before and after dispensing it? c. How will you explain the change from liquid soap to a foamy soap? 2.1. Homogeneous and Heterogeneous Mixtures 16 Unit 2: Separating Mixtures B. How can you compare a solution, a suspension, and a colloid? Create a diagram or flowchart to present solutions, suspensions, and colloid. Bibliography Brown, Theodore L. 2004. Chemistry: The Central Science (11th ed). Singapore: Pearson Education (Asia) Pte Ltd. Print. Chang, Raymond. 2010. Chemistry (10th ed). New York: McGraw-Hill. Print. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson Canada, 2011. Print. Silberberg, Martin S. 2009. Chemistry: The Molecular Nature of Matter and Change (5th ed). New York: McGraw-Hill. Whitten, Kenneth W. Chemistry (10th ed). Boston: Cengage Learning, 2013. Print. 2.1. Homogeneous and Heterogeneous Mixtures 17