Content Benchmark P.8.A.3

Students know methods for separating mixtures based on the properties of the components. E/S

MixturesA mixture is a combination of two or more pure substances that maintains its individual chemical properties. They are combinations of elements or compounds. Mixtures are not combined chemically, but instead are held together by physical forces called intermolecular forces, which help determine the properties of the substances.

Intermolecular forces occur when atoms of molecules are attracted to other molecules in a chemical bond. They cause atoms to form solid and liquid phases. In the gas phase, the molecules are too far apart for the intermolecular forces to have any effect.

There are four types of intermolecular forces; Ionic Bonding, Dipole-Dipole, Hydrogen bonding, and London dispersion forces (also known as van der Waal's forces).

1. Ionic Bonding, the strongest bond formed via intermolecular forces occurs when a molecule’s electronegativity value reaches 1.7 or greater caused by electrostatic attraction between molecules in a chemical bond.

2. Dipole-dipole forces, second strongest intermolecular force, are forces that exist between polar molecules of opposite charges of neighboring permanent dipoles. A positive nucleus of one molecule becomes attracted to the negative nuclei of another molecule.

3. Hydrogen bonding, stronger than dipole-dipole intermolecular forces, is forces that exist between molecules that have a hydrogen atom bonded to another atom that has a high electronegativity value. Because of the difference in electronegatvities, the hydrogen end (positive) will attract the negative end of the other molecule, creating a large partial charge which results in a very strong dipole-dipole force between the hydrogen atom of one molecule and the atom of another molecule.

4. London dispersion forces, the weakest intermolecular force, exists between all molecules. These are forces that exist between molecules when charge around an atom is not symmetrical creating an instantaneous dipole-dipole attraction. As atomic or molecular weight increases, so does the strength of the intermolecular force.

To learn more about intermolecular forces, go tohttp://www.science.uwaterloo.ca/~cchieh/cact/c123/intermol.html

To view an animation of the types of intermolecular forces, visithttp://cost.georgiasouthern.edu/chemistry/general/molecule/forces.htm, orhttp://www.wisc-online.com/objects/index_tj.asp?objID=GCH6804

Types of MixturesMixtures do not appear at first glance to be made of a single kind of matter. A mixture that has visibly different parts or is not distributed the same throughout are said to be heterogeneous. Heterogeneous mixtures may also exist in the three states of matter; solid, liquid, or gas. Other mixtures that do not contain visibly different parts or the same throughout are said to be homogeneous. Homogenous mixtures are also called solutions.

Figure 1. Types of Mixtures (From http://www.chem4kids.com/files/matter_solution.html)

Heterogeneous MixturesThere are two types of heterogeneous mixtures; suspensions and colloids. A suspension mixture is a mixture containing particles that tend to settle down to the bottom, if left undisturbed. For example, if one were to place sand, clay and water into a bottle, shake it, and then leave it on a table undisturbed, hours later the layer of sand would be settled or suspended at the very bottom with a layer of clay on top, followed by a layer of water on top of the layer of clay. As a result of sand’s density, because it is denser than that of the layer of clay and the layer of water, it settles at the bottom.

To learn more about types of heterogeneous mixtures, go tohttp://www.elmhurst.edu/~chm/vchembook/106Amixture.html

Homogeneous MixturesHomogeneous mixtures are mixtures that are consistent in appearance and composition throughout. Homogeneous mixtures are too thoroughly combined to be distinguished from one another by visual observation. Many homogeneous mixtures are commonly referred to as solutions or colloids.

ColloidsColloids are homogeneous mixtures in which particle sizes are larger than those in a solution but smaller than those in a suspension. Colloid mixtures may have components that exist in one or two states of matter. In a colloid mixture, particles will remain in its current state of matter, unlike a suspension mixture or heterogeneous mixture where if left undisturbed particles will settle to the bottom. For example, jelly, milk, blood, fog, glue, and paint will not settle but remain in its current state of matter.

Figure 2. Colloid particle sizes are greater than those normally discussed in many chemistry application (i.e., colloids are greater in size than atoms, molecules, and even polymers).

(From http://www.mpikg.mpg.de/english/03-colloidChemistry/researchProgram/colloidsare/index.html)

To learn more about colloid mixtures, go tohttp://www.mansfieldct.org/Schools/MMS/staff/hand/Chemvoc.htm

SolutionsA solution is a homogeneous mixture consisting of two or more pure substances in a single physical state of matter. Particles in a solution are very small and unable to be seen by the naked eye, such as atoms, molecules, or ions. They are evenly distributed throughout the solution in a uniform manner. For example, a spoonful from any part of the pitcher of lemonade will taste

equally sweet. In addition, regardless of how long a solution is left undisturbed under consistent conditions, the particles in the solution will not separate.

Figure 3. Solutions (From http://www.chem4kids.com/files/matter_solution.html)

Properties of SolutionsIn a solution, one substance is usually considered to the solute. A solute is a substance that is being dissolved or broken down in another substance in a solution. The substance that does the dissolving of the solute in a solution is called the solvent. For example, a solution of seawater consists of salt as the solute and water as the solvent. The salt is being dissolved in the water to make a solution of seawater.

Figure 4. Making a solution (From http://www.chem4kids.com/files/matter_solution.html)

Soluble and Insoluble SubstancesSubstances that are able to be dissolved in another substance are said to be soluble in that substance. For example, sugar and salt are both soluble in water because both solutes are able to be dissolved in water. Substances that are unable to be dissolved in another substance are said to be insoluble; unable to be dissolved in a solvent. Mercury and oil are examples of insoluble substances when placed in water. As a general rule of thumb, there will be usually more solvent than solute in a solution.

Figure 5. Concept map of mixtures (From http://qldscienceteachers.tripod.com/junior/chem/mixtures.html)

To learn more about Solvents, solutes, and solutions, go tohttp://www.science.uwaterloo.ca/~cchieh/cact/c120/solution.html

Factors Affecting Dissolving RateFactors that determine the rate at which a substance dissolves depend on the solubility of the solvent and solute. The rate at which a substance dissolves may be influenced by factors such as temperature, stirring, pressure, and surface area of dissolving substance.

Temperature and SolubilitySolubility may be influenced by temperature. The higher the temperature of the substance, the farther apart and faster the molecules will move due to the increase average kinetic energy of the molecules. The higher the temperature rises, the greater the average kinetic energy and as a result, molecules of the solvent, will on average begin to collide with the surface of the solute more frequently and with much more force. Thus, the solubility of most solid substances increases as the temperature of the solvent increases. For example, in warmer water, more solid will dissolve.

Conversely, the solubility of most gases becomes greater in colder temperatures rather than in warmer temperatures. The higher the temperature of a gas, the less soluble it becomes and the faster the gas molecules move, escaping from the liquid state. Thus, the solubility of the gaseous substances decreases as the temperature of the solvent increases.

To learn more about temperature and solubility, go to http://antoine.frostburg.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml

Stirring and Solubility

Solubility may also be influenced by stirring. Stirring affects the rate at which a solute dissolves. By agitating a solution, it will increase the rate of contact among colliding molecules of both solvent and solute with each other. By stirring a solution, one is also increasing the amount of kinetic energy, thus allowing for the molecule’s bonds to become weakened and broken.

Pressure and SolubilityPressure changes have minute effects on solid and liquid solutes’ solubility. However, an increase in pressure of a gaseous solute will have a greater effect on its solubility. Increasing the pressure of a gaseous solute, increases the number of collisions experienced between the particles of the gas and of the liquid, therefore, increasing the solution’s solubility. For example, removing a cap on a soda bottle releases pressure and the gaseous solute bubbles out of solution. Likewise, decreasing the pressure of a gaseous solute, decreases the interaction between particles of the solute and solvent and as well as its solubility.

Surface Area and SolubilityLastly, solubility may be influenced by the amount of surface area of the dissolving substance. The smaller particle is, the faster the solute will dissolve in the solvent. Dissolving solutes in a solution occurs at the surface of the solvent. The larger the surface area of the particle, the slower the process for breaking down the solute will be to the colliding molecules. Conversely, decreasing the size of the particles will increase the solute’s surface area, where one will be able to increase the rate of dissolution. For example, a spoonful of granulated sugar will dissolve faster than a sugar cube because the smaller particles in the granulated sugar render a much greater surface area to the colliding water molecules.

ActionEffect

solid solute gaseous soluteshake or stir increased rate decreased rate

increase temperature increased rate decreased ratedecrease temperature decreased rate increased rate

increase pressure N/A increased rateincrease solute's surface area increased rate N/A

Table 1. Factors Affecting Dissolving Rate (From http://www.geocities.com/CapeCanaveral/Lab/1643/solutions2.html)

To learn more about mixtures, visithttp://www.schoolforchampions.com/chemistry/mixtures.htm

Types of SolutionsThere are several possible combinations of solute to solvent physical states. The most common are solid, gaseous, liquid, and aqueous solutions.

Solution TypeComposition

ExamplesSolvent Solute

Gaseous gas gas air

Liquidliquid gas club sodaliquid liquid vinegarliquid solid Kool-Aid

Solidsolid liquid dental amalgamSolid solid steel, brass

Table 2. Composition of Solutions (From http://www.geocities.com/CapeCanaveral/Lab/1643/solutions1.html)

The most common solid solutions contain two or more metals and are called alloys. Alloys are constructed by melting the component metals, mixing them together, and then allowing them to cool. Properties of an alloy are different from the properties of the component metals. Alloys may possess characteristics such as greater strength, greater resistance to corrosion, and higher melting points. Solid solutions may be formed if the solute and the solvent share similar atomic radii, electronegativities, and electron configurations.

Gaseous solutions are mixtures with molecules spread relatively far apart and in constant random motion. When two or more gases are mixed together, the molecules quickly become intermingled in a uniformed composition. Because the molecules in a gas are so far apart, gaseous solutions may easily add more gas particles to change the composition of the solution. Properties of gaseous solutions depend on the properties of its components.

Within liquid solutions, the solvent and the solution are in a liquid state of matter. The solute may be a gas, a liquid, or a solid. Unlike gases, which can easily add more gas particles to change the composition of the solution, have limits to the amount of liquid solutes that may dissolve in liquid solvents. Liquid solutions that have pairs that may mix in any amount are called miscible, such as water and ethanol. Liquids that are unable to mix in any amount are called immiscible. Oil and water are an example of a liquid solution that is immiscible.

Solutions that are in water as the solvent are called aqueous solutions. Substances that are able to dissolve in water are categorized to whether they give way to ions or molecules in the solutions. Ionic compounds that dissolve separate into positive and negative ions and become enclosed by water molecules. These positive and negative solute ions are free to move around, allowing for an electric current to pass through the solution. A substance that dissolves in water separating into positive and negative ions and conducts an electric current is called an electrolyte.

To learn more about properties of solutions, go to http://www.chemtutor.com/solution.htm#prop.

Properties of Matter

Density and Solutions

Density is defined as the mass of an object divided by its volume; with metric units in grams per cubic centimeter. Using density as a property of matter, allows one to identify a substance. By sharing similar atomic size in a group, solid solutions will increase in density as one travels down a group. This increase in atomic radius causes each metal down a group to become more massive in its density. Equally, solid solutions will decrease in density as one goes across a period due to the decrease in atomic radius of the element. Hence, how much mass an atom can hold, depends of their volume, and their volume depends on their atomic radius.

To find about more about density, go to http://serc.carleton.edu/mathyouneed/densityexpl.html.

Conductivity and Solutions Conductivity of a solid solution will increase because conductivity of a single metal atom increases as one goes down a group on the periodic table. When moving down a group, the atom becomes larger, requiring less and less energy to remove its outer valence electrons away from the nucleus, thus making it easier to be taken away. In a period, when moving across from left to right, the amount of energy required to remove one electron from an atom increases for each following ionization; decreasing conductivity capabilities.

More information about solutions and conductivity can be found at http://scifun.chem.wisc.edu/homeexpts/CondTester/SolutionConductivity.htm

Magnetism and SolutionsSince atomic size determines outermost valence shell electrons, as the atomic radius increases, so does the magnetic properties of the atom. Although, the principal energy is the same for elements moving across a period, as the atomic radius decreases, the attraction between atoms increases due to their increase in atomic mass number of protons and electrons. Thus, magnetic properties of a solid solution will depend on the atomic size of both solute and solvent and placement on the periodic table.

To find out more about magnetism and solutions, go to http://amasci.com/freenrg/magh2o.html.

Solubility and SolutionsReactivity of an element’s solubility is dependent upon its atomic radius. As one moves down a group, atomic radius begins to increase, as a result, its solubility will begin to increase as well due to the space it occupies based on atomic size. The larger the atomic radius, the less it will fit in a given amount of solution, therefore making it more difficult to dissolve.

In addition, as one moves down and across on the periodic table, atoms will begin to share electrons no longer separate when placed in a solution. This is a result of the atom’s ionic radius and their ionic behavior. As one moves across a period, more electrons are transferred or pulled

off of metals, allowing for a greater net charge. For nonmetals, more of their protons will pull or gain electrons. This effect is the same for elements moving down a group.

To learn more about solubility and solutions, go tohttp://www.elmhurst.edu/~chm/vchembook/170Asolubility.html

Separating Components of a MixtureMixtures can be separated into their components by using physical methods; no chemical reactions involved. Deciding which separating technique to use depends on the different properties of the components, such as states of matter, solubility, boiling and melting points.

To learn more about separating mixtures in general, go to http://www.mikecurtis.org.uk/mixtures.htm

FiltrationFiltration is a technique that allows you to separate an insoluble solid from a liquid. The solid remains in the filter paper and the liquid goes through the paper into the beaker; for example, separating sand from water.

Figure 6. Filtration (From http://sciencepark.etacude.com/projects/separations/separation2.php)

To learn more about Filtration, go tohttp://dbhs.wvusd.k12.ca.us/webdocs/Matter/SeparationOfMixtures.html

ChromatographyChromatography is used to separate different colored dyes. The dyes travel up the chromatography paper at different distances before they cannot remain in solution. The more soluble dyes move further up than the less soluble ones, hence separating from each other. For example, separating dyes in inks, or chlorophyll in plants, ethanol as solvent.

In a chromatography technique, only a small amount of mixture samples are required. As the solvent moves up the paper the less soluble component will travel at a slower rate than those of more soluble components. Consequently the mixture will eventually separate into different colored spots as the solvent moves to the top. Sometimes, more sophisticated medium is used, such as thin plastic sheets coated with very fine pure aluminum oxide.

Figure 7. Chromatography (From http://sciencepark.etacude.com/projects/separations/separation2.php)

More information about chromatography can be found at http://www.rpi.edu/dept/chem-eng/Biotech-Environ/CHROMO/chromintro.html

SettlingHeterogeneous mixtures are not uniformed throughout. The solute is unable to dissolve in solvent, so instead it settles out. For example, oil and water. No matter how much you stir or shake the mixture, the solute will not dissolve in the solvent. Therefore, you will be able to see the mixture settle out and note the separation between oil and water.

To learn more about settling, go tohttp://pk014.k12.sd.us/chemistry/chapter%20two/notes%20elements,mixtures,%20and%20compounds.htm

Chemical Reactions The method appropriate to separate a mixture involves the behavior of the reactants and products when they react in a chemical reaction. Homogenous mixtures have a uniform composition throughout. It can be separated through evaporation and heating to boil the solvent involved. Heterogeneous mixtures have particles of different sizes and shapes and are not uniformed throughout. They are usually separated using distillation, filtration or settling methods.

An interesting site discussing the science of using chemical reactions to separate mixtures is found at http://science.csustan.edu/nhuy/chem3012/Experiments/abextraction.htm.

Distillation

Pouring a solution, like sugar and water, through filter paper will not separate the mixture; the sugar particles are too small. The best method is distillation; the water evaporates and the sugar is left behind.

Fractional distillation is a special type of distillation used to separate a mixture of liquids. Different liquids boil at different temperatures. When heated, they boil off and condense at different times. The apparatus features a fractionating column, which ensures that only the liquid boils at its boiling point, will pass into the condenser.

Figure 8. Types of Distillation (From http://sciencepark.etacude.com/projects/separations/separation2.php)

For normal distillation, the set-up is similar, except that the fractionating column is being removed. The curving structure of the fractionating column is to increase the surface area and encourage condensation of liquids with higher boiling points. Sometimes the column consists of a tube tightly packed with glass beads.

To learn more about distillation, go tohttp://www.docbrown.info/page01/ElCpdMix/EleCmdMix2.htm#METHODS

EvaporationEvaporation is a method in which molecules of a liquid escape from the surface and enters into the gaseous or vapor state. It is suitable to separate a soluble solid from a liquid. If the solution is heated, the liquid evaporates leaving the solid behind; for example, separating salt from water.

Figure 9. Evaporation (From http://www.hse.k12.in.us/staff/ebutzin/Documents/Chemistry/Matter/sepmix%20reading.doc)

To learn more about Evaporation via simulation, go tohttp://techalive.mtu.edu/meec/module01/EvaporationandTranspiration.htm

In general, more information about evaporation is found at http://www.bookrags.com/research/evaporation-woc/

MagnetsIn some of the materials in a mixture are magnetic (e.g., iron filings in salt), a magnet can be used to remove these magnetic materials from the nonmagnetic substrate.

Figure 10. Using a magnet to separate iron filings from sand (From http://www.ormuslike.info/ormuswater/magnetite-sand-1.html)

An interesting article on the use of “nano-magnets” for separating mixtures can be found at http://www.nanowerk.com/spotlight/spotid=2632.php.

Content Benchmark P.8.A.3

Students know methods for separating mixtures based on the properties of the components. E/S

Common misconceptions associated with this benchmark

1. Students incorrectly believe that when mixtures change in physical appearance, the substances also change in chemical make-up.Mixtures can be combinations of elements or compounds. Most substances found in nature are mixtures. A pure element or a pure compound is rarely found. Mixtures can be in any of the four phases of matter or they can be in combinations of different phases. For example, air is a mixture of gases, milk is a mixture of solids and liquids, alloys are mixtures of solids. Mixtures that do not appear to be distributed the same throughout are said to be heterogeneous, and those that are the same throughout are said to be homogeneous.

To learn more about mixtures, go tohttp://www.usoe.k12.ut.us/curr/Science/sciber00/8th/matter/sciber/matter.htm

2. Students incorrectly believe that when things dissolve, they disappear. When a solute dissolves into a solvent, the solute particles fill the spaces between the solvent particles. The solute is still present however now it is in solution. Solutions can be solids dissolved in liquids. They could also be gases dissolved in liquids (such as carbonated water). There can also be gases in other gases and liquids in liquids. If you mix things up and they stay at an even distribution, it is a solution. You probably won't find people making solid-solid solutions in front of you. They start off as solid/gas/liquid-liquid solutions and then harden at room temperature. Alloys with all types of metals are good examples of a solid solution at room temperature. A simple solution is basically two substances that are going to be combined. One of them is called the solute. A solute is the substance to be dissolved (sugar). The other is a solvent. The solvent is the one doing the dissolving (water).

To learn more about this misconception, go tohttp://chemed.chem.purdue.edu/genchem/topicreview/bp/ch3/solution.html#solute

3. Students incorrectly think that solutions can be separated by filtration.Solutions are homogeneous and cannot be filtered to separate into two different substances. Mixtures can be filtered. For example, sugar and water form a solution when mixed together. The sugar becomes evenly distributed throughout the solution, so that one portion is not sweeter than another. The dissolved portion of the solution (sugar) is called the solute and the dissolving portion (water) is the solvent. If more sugar is added to the solution, the entire solution becomes sweeter and we say that it is more concentrated. In solution, sugar and water have not lost their properties, only combined them. Pouring a solution, like sugar and water, through filter paper will not separate the mixture; the sugar particles are too small. The best method is distillation; the water evaporates and the sugar is left behind.To learn more about this misconception and the correct scientific understanding, go tohttp://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-2/Distillation-and-Filtration.html

Content Benchmark P.8.A.3

Students know methods for separating mixtures based on the properties of the components. E/S

Sample Test Questions

Content Benchmark P.8.A.3

Students know methods for separating mixtures based on the properties of the components. E/S

Answers to Sample Test Questions

Content Benchmark P.8.A.3

Students know methods for separating mixtures based on the properties of the components. E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. The Periodic Table of Comic BooksJames Holler and John P.Selegue developed an interactive website that allows the students to click on an element to see a list of comic book pages involving that element. Students may also click on the thumbnail in order to see a list of each full comic book page. The designers of the site recommend for the students to start with the element oxygen to see some of their greatest stuff. This is an educational website for students to learn more about the pure elements when discussing compounds and mixtures.

To access the website, go tohttp://www.uky.edu/Projects/Chemcomics/

2. Some Ideas for Teaching about Separating MixturesThis website provides the teacher suggestions for supplemental activities for addressing key concepts such as common physical changes in matter (size, shape; melting, freezing, dissolving, evaporating), changes in real-world contexts (size or shape of familiar objects, such as making snowballs, breaking glass, crumbling cookies, making clay models, carving wood, breaking bones; changes in state of water or other substances, such as freezing of ice cream, or ponds), and preparing mixtures and separating them into their component parts via various methods (filtration, magnets, density, chemical reaction, and evaporation).

To get these separating mixtures activities, go tohttp://elsci.lansingschools.net/unit-res/5b/Teaching-Dissolving-and-Mixtures.doc

A very good slide presentation about separating mixtures can be downloaded from http://webtech.cherokee.k12.ga.us/woodstock-hs/MikeYeager/Virtual%20Classroom/Assignments/Chapter%203/Separating%20Mixtures.pptNote: when downloading the presentation, the site will ask for a username and password. Click “cancel” and the presentation will then download.

This RAFT education department has created supplemental activities for teachers to implement in the classroom regarding mixtures. Students will be exposed to how scientists classify matter into either pure substances or mixtures. Mixtures can be evenly mixed throughout (homogeneous) or unevenly mixed (heterogeneous). Scientists use properties of matter to sort mixtures, just as students will in this activity. In the activities, the students

must separate the mixtures by their properties, noting visual properties such as size, color, shape. Students will use magnets, craft stick, and warm water to aide in their separating techniques.

To download the RAFT: Separating Mixtures activities, go tohttp://www.raft.net/ideas/Sorting%20it%20Out%20with%20Science.pdf

3. Online Activities-Separating MixturesThe Quia web provider, Bettina Lim, has developed an interactive website that may be used as an educational tool for understanding methods of separating mixtures. The website includes a variety of activities such as flash cards, matching, concentration, and word search which discuss filtration, evaporation, crystallization, distillation, and chromatography. Students will be first introduced to a list of common terms regarding the methods of separating mixtures then will be able to move forward in the online activities of their choice.

To access the online activity, go to http://quia.com/jg/33882.html

4. Interactive Media - Separating MixturesSeparating a mixture, getting it back into its individual parts, is a method of separating mixtures dependent on the type of mixture. In the following media piece, students will consider each of the presented mixtures and decide upon a method of separation. Though, there is more than one way to separate a mixture, students will observe a comment for each combination of mixture and method they chose. The provider, Coolschool.ca has also created a worksheet to accompany this activity.

To access the video, go to http://www.coolschool.ca/lor/SC7/unit6/U06L04.htm. Please note that this lab requires Adobe Shockwave software.

To access the accompanying worksheet, go to http://www.coolschool.ca/lor/SC7/unit6/U06L04/worksheet_U06L04.pdf