Middle+School+Chemistry+Chapter+5

=Chapter 5, Lesson 1: Water is a Polar Molecule= media type="custom" key="25050454" Brain Pop Water

Key Concepts

 * The water molecule, as a whole, has 10 protons and 10 electrons, so it is neutral.
 * In a water molecule, the oxygen atom and hydrogen atoms share electrons in covalent bonds, but the sharing is not equal.
 * In the covalent bond between oxygen and hydrogen, the oxygen atom attracts electrons a bit more strongly than the hydrogen atoms.
 * The unequal sharing of electrons gives the water molecule a slight negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms.
 * When a neutral molecule has a positive area at one end and a negative area at the other, it is a polar molecule.
 * Water molecules attract one another based on the attraction between the positive end of one water molecule and the negative end of another.

Objective
Students will be able to explain, on the molecular level, what makes water a polar molecule. Students will also be able to show in a drawing that the polar nature of water can explain some of water’s interesting characteristics and help explain its evaporation rate compared to a less polar liquid.

Materials Needed

 * Styrofoam water molecule models from Chapter 2, Lesson 2 (two per student)
 * Permanent markers (blue and red)
 * Isopropyl alcohol (70% or higher)
 * Water
 * Brown paper towel
 * Droppers

media type="file" key="water_balloon.wmv" width="300" height="300"

Remember that in Chapters 1 & 2, you investigated the behavior of water at different temperatures and explored the state changes of water. Many of the explanations were based on the idea that water molecules are attracted to one another. In Chapter 4 you looked at the covalent bonding between oxygen and hydrogen, which creates the water molecule. Now you will look more closely at the details of the covalent bonds in a water molecule to understand why water molecules are attracted to one another.


 * 1) Water Fountain
 * 2) media type="file" key="polar_water_molecule.swf" width="360" height="270"
 * 3) What do you notice about the way water molecules orient themselves? Why do water molecules attract one another like this? Answer these questions on your activity sheet & complete the first section.
 * 4) Watch the Brain Pop movie about water (link above)
 * 5) The bonds //within// molecules and the polar attractions //between// molecules is different. The interaction between the oxygen of one water molecule and the hydrogen of another is different than the sharing of electrons between the oxygen and the hydrogens within the water molecule itself. Attractions on Different Levels
 * 6) Complete the activity on your sheet. Mark the positive and negative areas on a water molecule by color-coding your Styrofoam ball model.
 * 7) Do the activity to compare the rate of evaporation between water and alcohol.
 * 8) Complete the Take It Further section of your activity sheet

=Chapter 5, Lesson 2: Surface Tension= media type="custom" key="25050500"media type="custom" key="25050532"

Key Concepts

 * The attraction of molecules at the surface of a liquid is called surface tension.
 * The polarity of water molecules can help explain why water has a strong surface tension.

Objective
Students will be able to explain, on the molecular level, the effects of polarity on water’s surface tension.

Materials Needed
 * 1 clear plastic cup
 * Water
 * 1 standard size paper clip
 * 1 large paper clip
 * Isopropyl alcohol (70% or higher)
 * Dish detergent in cup
 * Test tube
 * 2 pennies
 * 2 droppers
 * 2 toothpicks
 * 2 paper towels

media type="file" key="surface_tension.wmv" width="300" height="300"
 * 1) Watch the demonstration & then watch the above video. Answer the question on your activity sheet #1.
 * 2) [[image:Water strider.jpg]][[image:Molecule.jpg]] Why do you think water has such a strong surface tension?
 * 3) Complete the experiment on your activity sheet & record your observations.
 * 4) [[image:water beads.jpg]]Water's surface tension is based on the attractions between water molecules at the surface and the water molecules in the rest of the water. A water molecule beneath the surface feels attractions from all the molecules around it. But the molecules at the surface only feel attractions from the molecules next to them and beneath them.
 * 5) Define //surface tension// in your science notebook.
 * 6) Compare the surface tension of water and alcohol. Record your observations on your activity sheet.
 * 7) [[image:Water&Alcohol.jpg]][[image:Water&Alcohol2.jpg]] Water molecules are polar and they are very attracted to each other. Alcohol molecules are polar in only one area, making them somewhat attracted to each other.
 * 8) How does detergent affect water's surface tension? Complete the experiment and record your observations on your activity sheet.
 * 9) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_2/water_and_detergent_big.jpg width="388" height="145"]] Detergent is made from molecules that have a charged end a a longer uncharged end. Th detergent molecules spread out over the surface of the water with the charged end in the water and the uncharged end sticking out.
 * 10) Complete the Take It Further section of your activity sheet.

media type="file" key="water_on_paper_towel.wmv" width="300" height="300" media type="file" key="water_on_wax_paper.wmv" width="300" height="300"

=**Extra Lesson: Surface Tension and Molecular Bonds=

Lesson Objective
Students will recall what they have learned about the structure of matter regarding atoms and molecules and their bonds. They will relate that knowledge to surface tension and the tendency of drops to acquire and conserve a spherical shape. Surface Tension

=Chapter 5, Lesson 3: Why Does Water Dissolve Salt= media type="custom" key="25064364"

Key Concepts

 * The polarity of water molecules enables water to dissolve many ionically bonded substances
 * Salt (sodium chloride) is made from positive sodium ions bonded to negative chloride ions
 * Water can dissolve salt because the positive part of water molecules attracts the negative chloride ions and the negative part of water molecules attracts the positive sodium ions.
 * The amount of a substance that can dissolve in a liquid (at a particular temperature) is called the //solubility// of the substance
 * The substance being dissolved is called the solute, and the substance doing the dissolving is called the solvent

Objective
Students will be able to explain, on the molecular level, why water can dissolve salt. Students will be able to identify the variables in their experiment. Students will also be able to explain why a less polar liquid, such as alcohol, is not good at dissolving salt.

Materials Needed

 * construction paper
 * scissors
 * tape or glue
 * water
 * isopropyl alcohol
 * salt
 * balance
 * 2 clear plastic cups
 * 2 small plastic cups
 * graduated cylinder




 * 1) What is it about water molecules and the ions in salt that might make water able to dissolve salt? Answer the question on your activity sheet.
 * 2) Complete the Question to Investigate section of your activity sheet. You may laminate the ions if desired.

media type="file" key="sodium_chloride_dissolving.wmv" width="300" height="300" 3. Conduct an experiment to find out whether water or isopropyl alcohol would be better at dissolving salt. Record your observations on your activity sheet. 4. Complete the Take It Further section on your activity sheet.

=Chapter 5, Lesson 4: Why Does Water Dissolve Sugar?= media type="custom" key="25064680"

Key Concepts

 * For a liquid to dissolve a solid, the molecules of the liquid and solid must attract one another
 * The bond between the oxygen and hydrogen atoms (O-H bond) in sugar (sucrose) gives the oxygen a slight negative charge and the hydrogen a slight positive charge. Sucrose is a polar molecule
 * The polar water molecules attract the negative and positive areas on the polar sucrose molecules which makes sucrose dissolve in water
 * A non-polar substance like mineral oil does not dissolve a polar substance like sucrose

Objective
Student will be able to explain, on the molecular level, how the polar characteristic of water and sugar interact so that water dissolves sugar. Students will be able to identify and control the variables in their experiment. Students will also be able to explain why a non-polar liquid, such as mineral oil, is not good at dissolving sugar.

Materials Needed

 * M&M's
 * water
 * mineral oil
 * isopropyl alcohol
 * small white plastic plate
 * 3 clear plastic cups
 * white paper


 * 1) Open a package of M&M's and look at the outside candy coating. Break one open and look closely at the coating from the inside. What do you think the coating of a M&M is made of? Have you ever noticed what happens to a M&M when it gets wet?
 * 2) Complete the procedure as outlined on your activity sheet and record your observations.
 * 3) Sugar is made of large molecules called sucrose. Each sucrose molecule is made of atoms that are covalently bonded. Make a model of a sucrose molecule with your chemistry kit. [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/sucrose_1.jpg]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/sucrose_2.jpg]]
 * 4) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/water_dissolves_sucrose_1.jpg width="183" height="183"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/water_dissolves_sucrose_2.jpg width="185" height="185"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/water_dissolves_sucrose_3.jpg width="191" height="191"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/water_dissolves_sucrose_4.jpg width="177" height="177"]] One sugar cube is made up of at least one billion trillion sucrose molecules. When sugar dissolves, these whole sucrose molecules separate from one another. The molecule itself doesn't come apart: The atoms that make up each molecule stay together as a sucrose molecule.
 * 5) Review the animation here: Sucrose
 * 6) media type="file" key="water_dissolves_sucrose.wmv" width="300" height="300" Sugar molecules are attracted to each other and held together by the attraction between these polar areas of the molecules.
 * 7) Complete the experiment to compare how well water, alcohol, and oil dissolve the sugar and color coating of an M&M. Make your prediction if you think water, alcohol, or oil will be better at dissolving the sugar and color coating of an M&M. Write this on your activity sheet.
 * 8) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/water.jpg width="231" height="231" caption="Water"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/isopropyl_alcohol.jpg width="270" height="270" caption="isopropyl alcohol"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/oil.jpg width="270" height="270" caption="Oil"]]W ater molecules are polar. The alcohol is 30% water & 70% alcohol. Oil molecules are not polar.
 * 9) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_4/citric_acid.jpg]] This is a model of a citric acid molecule. Citric acid is the substance that gives lemons, limes, grapefruit, and oranges their tangy sour taste. Citric acid is very soluble in water and is dissolved in the water in the fruit. Why do you think citric acid is so soluble in water?

=Chapter 5, Lesson 5: Using Dissolving to Identify an Unknown= media type="custom" key="25079642"

Key Concepts

 * Different substances are made from different atoms, ions, or molecules, which interact with water in different ways
 * Since dissolving depends on the interaction between water and the substance being dissolved, each substance has a characteristic solubility

Objective
Students will be able to identify and control variables when designing a solubility test. Students will be able to explain why different substances dissolve to different extents in water.

Materials Needed

 * balance
 * graduated cylinder
 * water
 * 4 clear plastic cups
 * 2 small plastic cups
 * salt
 * sugar
 * cereal balls
 * zip-closing plastic bag
 * salt
 * Epsom salt
 * MSG
 * sugar
 * coarse kosher salt
 * water
 * black construction paper
 * masking tape
 * permanent marker
 * magnifier
 * 5 small plastic cups
 * 56 clear plastic cups
 * paper towels


 * 1) Watch the demonstration that shows different substances have different solubilities. Record your observations on your activity sheet.
 * 2) Review the question to investigate. Can you identify the unknown crystal by the way it looks? Follow the instructions on your activity sheet & record your observations.
 * 3) A solubility test provides useful information, if it controls variables well. Is it better to use the same volume (like a teaspoon or 5 mL) or the same mass (like 5g) of each crystal? Why? Watch the demonstration and record your observations on your activity sheet.
 * 4) In the solubility test you will do, you will need to measure equal amounts of the five crystals. How will you measure equal amounts?
 * 5) You will compare the solubility of four different household crystals--salt (sodium chloride), Epsom salt (magnesium sulfate), MSG (monosodium glutamate), and sugar (sucrose). You will also test an unknown crystal that is chemically the same as one of the other crystals. Because it has the same solubility as one of the crystals you are testing, you should be able to identify the unknown. Complete the procedure on your activity sheet & record your observations.
 * 6) Conduct another test to confirm the identify of the unknown. (This will involve allowing the solutions to sit overnight - be sure to return to the activity sheet during your next lesson & complete the procedure)
 * 7) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_5/four_crystals_1.jpg width="180" height="180" caption="Magnesium sulfate"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_5/four_crystals_2.jpg width="180" height="180" caption="Monosodium glutamate"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_5/four_crystals_3.jpg width="180" height="180" caption="Sodium chloride"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_5/four_crystals_4.jpg width="180" height="180" caption="Sucrose"]] Because these substances are made up of different atoms and ions bonded together differently, they interact with water differently, giving them each their own characteristic solubility.
 * 8) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_3/salt_dissolving_1.jpg width="180"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_3/salt_dissolving_2.jpg width="180"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_3/salt_dissolving_3.jpg width="180"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_3/salt_dissolving_4.jpg width="180"]] When salt dissolves, why are water molecules attracted to the sodium and chloride ions?
 * 9) Review the pictures from lesson 4 of water dissolving sugar. When sugar dissolves, why are water molecules attracted to sucrose molecules?
 * 10) Record the similarities and differences between salt dissolving in water and sugar dissolving in water on your activity sheet.

=Chapter 5, Lesson 6: Does Temperature Affect Dissolving?= media type="custom" key="25079618"

Key Concepts

 * Adding energy (heating) increases molecular motion
 * Increased molecular motion competes with the attraction between solute molecules and tends to make them come apart more easily
 * Increased molecular motion causes more solvent molecules to contract solute molecules and pull on them with more force, usually resulting in more dissolving
 * Since different substances are made from different atoms, ions, or molecules, increased temperature will affect their dissolving to different extents

Objective
Students will be able to identify and control variables to design an experiment to see whether the temperature of a solvent affects the speed at which a solute dissolves. Students will be able to explain, on the molecular level, why increasing temperature increases the rate of dissolving.

Materials Needed

 * M&M (3 of the same color)
 * 3 clear plastic cups
 * 1 sheet of white paper
 * Room-temp water
 * hot water (about 50° C)
 * cold water (about 5° C)
 * graduated cylinders
 * salt
 * sugar
 * 2 small cups


 * 1) Design an experiment to investigate whether the temperature of water affects the amount of M&M coating that dissolves. What could you investigate about M&M's dissolving in water? Complete the procedure on your activity sheet and record your observations.
 * 2) What are the differences in the way water molecules move in cold, room-temperature, and hot water? Answer questions 3-5 on your activity sheet.
 * 3) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_6/salt_dissolve_hot_cold.jpg width="210" height="210"]][[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_6/sugar_dissolve_hot_cold.jpg width="210" height="210"]]Watch the demonstration and record your observations on your activity sheet.
 * 4) Complete the Take It Further section of your activity sheet

=Chapter 5, Lesson 7: Can Liquids Dissolve in Water= media type="custom" key="25099610"

Key Concepts

 * Liquids have characteristic properties based on the molecules they are made of
 * The properties of liquids depend on the attractions the molecules of the liquid have for each other and for other substances
 * Liquids can dissolve certain other liquids, depending on the attractions between the molecules of both liquids
 * Polar liquids, like water, dissolve other liquids which are polar or somewhat polar
 * Polar liquids, like water, do not dissolve nonpolar liquids like oil

Objective
Students will identify and control variables to help design a solubility test for different liquids in water. Students will be able to explain, on the molecular level, why certain liquids, but not all, will dissolve in water. They will also be able to explain that the solubility of a liquid is a characteristic property of that liquid.

Materials Needed

 * 3 clear plastic cups
 * water
 * food coloring
 * 3 straws or popsicle sticks
 * isopropyl alcohol
 * 2 100-mL graduated cylinders
 * mineral oil
 * corn syrup
 * 5 small cups
 * permanent marker
 * laminated index card
 * blue water
 * yellow isopropyl alcohol
 * 2 droppers
 * toothpick


 * 1) Watch the demonstration and record your observations on your activity sheet.
 * 2) Complete the experiment and record your observations on your activity sheet.
 * 3) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_7/isopropyl_alcohol.jpg width="210" height="210" caption="Isopropyl Alcohol"]]Look at the bond between oxygen and hydrogen in one area of the alcohol molecule.
 * 4) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_7/oil.jpg width="210" height="210" caption="Mineral Oil"]]Carbon (darker grey) and hydrogen atoms share electrons rather evenly. This means that the bonds in mineral oil are nonpolar, so water molecules and mineral oil molecules are not attracted to each other.
 * 5) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_7/glucose.jpg width="210" height="210" caption="Glucose"]]Corn syrup is mostly glucose but also contains a similar sugar, fructose. Look at the bonds between oxygen and hydrogen.
 * 6) Complete the Take It Further portion of your activity sheet.
 * 7) Watch the demonstration and record your observations on your activity sheet.

=Chapter 5, Lesson 8: Can Gases Dissolve in Water?= media type="custom" key="25099702"

Key Concepts

 * Gases can dissolve in water
 * The dissolving of a gas in water depends on the interaction between the molecules of the gas and the water molecules
 * The amount of gas that can be dissolved in water depends on the temperature of the water
 * More gas can dissolve in cold water than in hot water

Objective
Students will be able to explain, on the molecular level, how a gas dissolves in water. They will also be able to explain why the gas comes out of solution faster in warm water than in cold water.

Materials Needed

 * club soda
 * 3 clear plastic cups
 * 1 M&M
 * pipe cleaner
 * hot water
 * cold water
 * 2 deli containers


 * 1) Watch the demonstration and record your observations on your activity sheet. Carbonated water is made of carbon dioxide gas dissolved in water.
 * 2) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_8/carbon_dioxide.jpg width="210" height="210" caption="Carbon Dioxide"]]A molecule of carbon dioxide has a slight negative charge near the oxygen and a slight positive charge near the carbon.
 * 3) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_8/carbon_dioxide_in_water.jpg width="210" height="210" caption="CO2 dissolved in water"]]In carbonated water, molecules of carbon dioxide are thoroughly mixed and dissolved in water.
 * 4) Complete the experiment to investigate how can you make carbon dioxide gas come out of solution and record your observations on your activity sheet.
 * 5) Does carbon dioxide stay dissolved better in water that is warmed or water that is cooled? Complete the experiment to find out and record your observations on your activity sheet.
 * 6) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_8/solubility_curve_carbon_dioxide.jpg width="210" height="127"]]This graph shows how the concentration of carbon dioxide in water changes with temperature.
 * 7) Complete the Take It Further section of your activity sheet.
 * 8) media type="file" key="mentos.wmv" width="300" height="300"Answer question 14 after viewing this video.

=Chapter 5, Lesson 9: Temperature Changes in Dissolving= media type="custom" key="25100014"

Key Concepts

 * The process of dissolving can be //endothermic// (temperature goes down) or //exothermic// (temperature goes up)
 * When water dissolves a substance, the water molecules attract and "bond" to the particles (molecules or ions) of the substance causing the particles to separate from each other
 * The "bond" that a water molecule makes is not a covalent or ionic bond. It is a strong attraction caused by water's polarity
 * It takes energy to break the bonds between the molecules or ions of the solute
 * Energy is released when water molecules bond the solute molecules or ions
 * If it takes more energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes down (endothermic)
 * If it takes less energy to separate the particles of the solute than is released when the water molecules bond to the particles, then the temperature goes up (exothermic)

Objective
Students will be able to identify variables in an experiment to find out how much the temperature increases or decreases as each of four solute dissolves in water. Students will be able to correctly classify the process of dissolving as either exothermic or endothermic for each solute. Students will be able to explain that the temperature changes in dissolving are a result of the amount of energy released compared to the amount of energy used as "bonds" are formed during the process of dissolving.

Materials Needed

 * Potassium chloride
 * calcium chloride
 * sodium carbonate
 * sodium bicarbonate
 * water
 * 5 small cups
 * graduated cylinder
 * thermometer
 * gram balance
 * safety glasses
 * thermometer
 * hot & cold packs

> media type="file" key="energy_and_dissolving.swf" width="360" height="270"
 * 1) Watch the demonstration and record your observations on your activity sheet.
 * 2) Scientists describe temperature changes that occur when substances interact as either //endothermic// or //exothermic.// When the temperature decreases, as it does in a cold pack, the process is endothermic. When the temper ature increases, as it does in the hot pack, the process is exothermic
 * 3) Conduct the experiment to compare how much the temperature changes when four household substances dissolve in water. Record your observations on your activity sheet.
 * 4) media type="file" key="breaking_and_making_bonds.swf" width="360" height="270"**It is important to remember that // energy is required to pull apart atoms, ions, or molecules that are attracted to each other. But when atoms, ions, or molecules come together, energy is released //**
 * 1) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_9/exothermic_dissolving.jpg]]The process of dissolving is exothermic when more energy is released when water molecules "bond" to the solute than is used to pull the solute apart.
 * 2) [[image:http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_9/endothermic_dissolving.jpg]]The process of dissolving is endothermic when less energy is released when water molecules "bond" to the solute than is used to pull the solute apart.
 * 3) media type="file" key="hand_warmer.wmv" width="300" height="300"In the hand warmer, the water molecules and the ions of the solute come together to form a crystal.
 * 4) Temperature Change Alcohol in Water Review the video and answer the related questions on your activity sheet

=Chapter 5: Unit Assessment=
 * 1) Complete student reading for chapter 5
 * 2) Complete the unit assessment