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How to Use This Presentation

By Jesus Nelson,2014-05-29 22:38
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How to Use This Presentation

How to Use This Presentation

Table of Contents

    Section 1 Solutions and Other Mixtures

Section 2 How Substances Dissolve

Section 3 Solubility and Concentration

    Objectives

     Distinguish between heterogeneous mixtures and homogeneous mixtures.

     Compare the properties of suspensions, colloids, and solutions.

Give examples of solutions that contain solids

    or gases.

    Bellringer

    Mixtures of solids and liquids are all around us, but are all mixtures classified in the same way?

    Make a list of at least five mixtures that you have encountered today. List the components of each mixture in general terms, if possible. Remember a mixture

    can be two solids, a liquid/solid, or two liquids. Example: mudsoil and

    water, raisin bran cerealbran flakes and raisins.

    What similarities or differences in the mixtures on your list could be used to classify all mixtures?

    Heterogeneous Mixtures

     The amount of each substance in different samples of a heterogeneous

    mixture varies.

     Example: Any two shovelfuls of dirt from a garden would not be exactly the

    same.

     A suspension is a mixture in which large particles of a material are more or less evenly dispersed throughout a liquid or gas.

     Example: natural orange juice, which contains particles of pulp.

Particles in a suspension may settle over time, and may be filtered out.

    Suspension

    Heterogeneous Mixtures, continued

     Some combinations of liquids will not mix, but will separate spontaneously.

     Example: Oil and vinegar in salad dressing separates into two layers.

Liquids that do not mix with each other are immiscible.

     One way to separate two immiscible liquids is to carefully pour the less dense liquid off the top. This is called decanting.

    Comparing Miscible and Immiscible Liquids

Heterogeneous Mixtures, continued

     A colloid is a mixture consisting of tiny particles that are intermediate in size between those in solutions and those in suspensions and that are suspended in a liquid, solid or gas.

Particles in a colloid are too small to settle out.

     However, particles in a colloid are large enough to scatter light that passes through: this is called the Tyndall effect.

    Colloids

    Heterogeneous Mixtures, continued

     Examples of familiar materials that are colloids include gelatin desserts, egg whites, and blood plasma.

Some immiscible liquids can form colloids.

     An emulsion is any mixture of two or more immiscible liquids in which one liquid is dispersed

    in the other.

    Emulsions

    Homogeneous Mixtures

     Homogeneous mixtures not only look uniform, but

    are uniform.

     Example: salt water, which looks uniform even when you examine it under a microscope

     A solution is a homogeneous mixture of two or

    more substances uniformly dispersed throughout

    a single phase.

     In a solution, the solute is the substance that dissolves in the solvent.

     The solvent is the substance in which the solute dissolves.

    Homogeneous Mixture

    Solutions

    Solutes, Solvents, and Solutions

    Homogeneous Mixtures, continued

     Miscible liquids mix to form solutions.

One way to separate miscible liquids is by distillation, which works when the

    two miscible liquids have different boiling points.

     Water is a common solvent, but some liquid solutions contain no water.

     Example: Fuels such as gasoline, diesel fuel, and kerosene are made from

    a liquid solution called petroleum, also called crude oil.

     Components of crude oil are separated by fractional distillation.

    Fractional Distillation in Refineries

    Homogeneous Mixtures, continued

Other states of matter can also form solutions.

     The air you breathe is a solution of nitrogen, oxygen, argon, and other

    gases.

     The liquid element mercury dissolves in solid silver to form a solution called

    an amalgam, which can be used to fill cavities in teeth.

An alloy is a solid or liquid mixture of two or

    more metals.

    Objectives

     Explain how the polarity of water enables it to dissolve many different substances.

     Relate the ability of a solvent to dissolve a solute to the relative strengths of forces between molecules.

     Describe three ways to increase the rate at which a solute dissolves in a solvent.

     Explain how a solute affects the freezing point and boiling point of a solution. Bellringer

    One mixture you may be familiar with is the one formed when sugar is added to a glass of tea or lemonade. Eventually, the sugar dissolves, and the entire glass tastes sweeter than before.

    1. Does the sugar you add to the tea or lemonade dissolve faster before or after ice is added? What happens in each instance?

    2. If more sugar is added to the tea or lemonade than will dissolve, what happens to the remaining undissolved sugar?

    3. When there is sugar on the bottom of the glass, is the top or bottom of the tea or lemonade sweeter than the rest?

    4. What can you do to help the sugar on the bottom of the glass dissolve?

    Water: A Common Solvent

     Many different substances can dissolve in water.

    For this reason, water is sometimes called the universal solvent.

Water can dissolve ionic compounds because of its structure: it is a polar

    compound, which is a molecule that has an uneven distribution of electrons.

     Because they are polar, water molecules

    attract both the positive and negative ions of

    an ionic compound.

    Water: A Common Solvent, continued

     Polar water molecules pull ionic crystals apart, as shown below. Water: A Common Solvent, continued

     Water exhibits hydrogen bonding: the intermolecular force occurring when a

    hydrogen

    atom that is bonded to a highly electronegative atom of one molecule is attracted to two unshared electrons of another molecule.

Hydrogen bonding determines many of water’s unique properties.

     Hydrogen bonding enables water to dissolve many molecular compounds, such as sugar.

    Hydrogen Bonding

    Water: A Common Solvent, continued

     A rule of thumb in chemistry is that like dissolves like.

     This rule means that a solvent will dissolve substances that are like the

    solvent in

    molecular structure.

A nonpolar compound is a compound whose electrons are equally

    distributed among its atoms.

     A nonpolar compound usually will not dissolve in water, because its

    intermolecular forces do not match with those of water. Like Dissolves Like

    The Dissolving Process

     According to the kinetic theory of matter, water molecules in a glass of tea are always moving.

     When sugar is poured into the tea, water molecules collide with sugar molecules.

     Sugar molecules form a solution with water molecules at the surface of the sugar crystals.

     As layers of sugar molecules leave the crystal, more layers are uncovered and dissolve among the

    solvent (water) molecules in the same way.

    Dissolving Process

    The Dissolving Process, continued

     Solutes with a larger surface area dissolve faster.

     More solute particles are exposed to the solvent.

     Stirring or shaking a solution helps the solute dissolve faster.

     Dissolved solute particles diffuse throughout the solution faster, allowing

    more solute particles to dissolve.

Solutes dissolve faster when the solvent is hot.

     Collisions occur between solute and solvent particles more frequently and

    with more energy.

    Surface Area

    Factors Affecting the Rate of Dissolution

    The Dissolving Process, continued

     Solutes affect the physical properties of a solution.

     Examples:

     If you dissolve salt in water, it will boil at a higher temperature and freeze

    at a lower temperature.

     The coolant mixture of

    ethylene glycol (antifreeze)

    with water keeps a car’s

    radiator fluid from freezing in

    winter or boiling in summer.

    Objectives

     Explain the meaning of solubility and compare the solubilities of various substances.

     Describe dilute, concentrated, saturated, and supersaturated solutions.

     Relate changes in temperature and pressure to changes in solubility of solid and gaseous solutes.

     Express the concentration of a solution as molarity, and calculate the molarity of a solution given the amount of solute and the volume of the solution. Bellringer

    Many solutions can be found in your home. Most of these are not pure solutions, but contain several substances dissolved in a single solvent, such as water. The labels on products often indicate not only the ingredients that are in the solution, but also information about the concentration (the amount of solute in a volume of solution) of the main ingredient.

    Examine the labels on the next slide, and answer the items that follow. Bellringer, continued

     1. What is the solvent in each solution?

    2. What is the solute in each solution? Is there only one solute in each solution? Explain your answer.

3. How would the label for bleach differ for two jugs, one containing

    500 mL of bleach and the other containing 1.0 L of bleach?

    Explain your answer.

    Bellringer, continued

    4. Would the labels for vinegar and club soda differ for two containers with different total volumes? Explain your answer.

    5. Are all of the solutes dissolved solids? Explain your answer.

    Solubility in Water

     Solubility is the maximum amount of a solute that will dissolve in a given quantity of solvent at a given temperature and pressure.

     Some substances, such as oil, are insoluble in water, meaning they never

    dissolve.

     Other substances are said to be soluble in water because they dissolve

    easily in water.

     However, there is often a limit to how much of a substance will dissolve.

Different substances have different solubilities.

    Solubility of a Solid in a Liquid

    Solubility in Water, continued

     To express how much of a substance can dissolve in a solvent, you need to use the concentration.

     Concentration is the amount of a particular substance in a given volume of solution.

     A solution whose ratio of solute to solvent is relatively high is referred to as

    concentrated.

     A solution whose ratio of solute to solvent is relatively low is referred to

    dilute.

    Concentration

    Solubility in Water, continued

     An unsaturated solution contains less than the maximum amount of solute that can dissolve.

     A saturated solution is at a point where no more solute can be dissolved under the same conditions.

     If you add more solute to a saturated solution, it will simply fall to the bottom of the

    container.

     A supersaturated solution holds more dissolved solute than is required to reach equilibrium at a given temperature.

     To make a supersaturated solution, you raise the temperature of a solution, dissolve more

    solute, then

    let the solution cool again.

    Solubility in Water, continued

     Gases can also dissolve in water.

     Unlike solid solutes, gaseous solutes are less soluble in warmer water than they are in colder water.

     Example: Soda goes flat quickly at room temperature.

     The solubility of gases also depends on pressure. Lowered pressure of gas

    above a solution leads to dissolved gas bubbling out of the solution.

     Example: When a can of soda is opened, carbon dioxide gas that had been dissolved in

    the soda bubbles out of solution.

     Example: If a scuba diver surfaces too quickly, dissolved nitrogen gas in the bloodstream

    bubbles out of solution, which causes a painful condition called the bends.

    Pressure, Temperature, and Solubility of Gases

    Concentration of Solutions

     There are several ways to express the concentration of solutions, but one of

    the most useful ways is by using molarity: moles of dissolved solvent per liter of solution.

    Math Skills

    Molarity Calculate the molarity of sodium carbonate, NaCO, in a solution of 23

    38.6 g of solute in 0.500 L

    of solution.

1. List the given and unknown values.

     Given: mass of sodium carbonate = 38.6 g

     volume of solution = 0.500 L

     Unknown: molarity, amount of NaCO in 1 L 23

     of solution

    Math Skills, continued

    2. Write the equation for moles NaCO and molarity. 23

Math Skills, continued

    3. Find the number of moles of NaCO and 23

    calculate molarity.

    Concentration of Solutions, continued

Other measures of solution concentration can

    be used.

     These include:

     mass percent (grams of solute per 100 g

    of solution)

     Ingredients in many food and household products use mass percent. 6 parts per million (grams of solute per 10 g

    of solution)

     Used for very small concentrations, such as for environmental

    regulations.

    Concept Mapping

    Understanding Concepts

    1. What characteristic of a molecular compound is

    most likely to cause the compound to be very soluble in water?

     A. hydrogen content

     B. low boiling point

     C. high polarity

     D. small size

    Understanding Concepts

    1. What characteristic of a molecular compound is

    most likely to cause the compound to be very soluble in water?

     A. hydrogen content

     B. low boiling point

     C. high polarity

     D. small size

    Understanding Concepts

    2. What factor differentiates a colloid from a suspension?

     F. Suspensions contain larger particles in solution.

     G. Colloids have smaller particles that do not settle out.

     H. A colloid is a type of solution, while a suspension is a type of mixture.

     I. The solvent in a suspension is polar, while the solvent in a colloid is

    nonpolar.

    Understanding Concepts

    2. What factor differentiates a colloid from a suspension?

     F. Suspensions contain larger particles in solution.

     G. Colloids have smaller particles that do not settle out.

     H. A colloid is a type of solution, while a suspension is a type of mixture.

     I. The solvent in a suspension is polar, while the solvent in a colloid is

    nonpolar.

    Understanding Concepts

    3. Adding a crystal to a supersaturated solute causes crystallization of the solute

    because

     A. as the added crystal dissolves, it causes the solution to cool.

     B. the added crystal provides a surface on which the solute can form crystal.

     C. as the added crystal dissolves, the level of supersaturation becomes

    too high.

     D. the added crystal decreases the solubility of the solute molecules,

    causing them to crystallize.

    Understanding Concepts

    3. Adding a crystal to a supersaturated solute causes crystallization of the solute

    because

     A. as the added crystal dissolves, it causes the solution to cool.

     B. the added crystal provides a surface on which the solute can form crystal.

     C. as the added crystal dissolves, the level of supersaturation becomes

    too high.

     D. the added crystal decreases the solubility of the solute molecules,

    causing them to crystallize.

    Understanding Concepts

    4. When paint thinner is added to latex paint, the mixture quickly separates into

    two distinct layers, but water mixes into the paint easily. Based on this

    observation, what can you infer about the type of solvents used in latex paint

    and in paint thinner?

    Understanding Concepts

    4. When paint thinner is added to latex paint, the mixture quickly separates into

    two distinct layers, but water mixes into the paint easily. Based on this

    observation, what can you infer about the type of solvents used in latex paint

    and in paint thinner?

Answer: The solvent in latex paint has a polar

    molecule like water. Paint thinner contains

    nonpolar compounds.

    Reading Skills

     If you rinse greasy hands in water, the grease does not wash off because the molecules of the compounds in grease are nonpolar, while the molecules of water are polar. If you use soap, though, the grease washes away. The molecules of soap are long chains of atoms with a polar end and a nonpolar end. The nonpolar ends surround grease molecules, dissolving them. Then the polar ends of the soap molecules interact with water to make the whole group soluble in water.

    5. When the polar end of soap reacts with calcium ions, it forms a salt that is not very soluble in water. How does this explain the observation that soap does not work well in hard water, which contains dissolved calcium ions?

    Reading Skills

    5. When the polar end of soap reacts with calcium ions, it forms a salt that is not

    very soluble in water. How does this explain the observation that soap does

    not work well in hard water, which contains dissolved calcium ions?

    Answer: The soap molecules react with calcium ions to form a solid that does not

    dissolve. Therefore the soap is not available to cause nonpolar molecules to

    dissolve in water.

    Interpreting Graphics

     F. It forms a suspension of small particles.

     G. The crystal breaks apart into pairs of positive and negative ions.

     H. Ions separate from one another and interact with

     water molecules.

     I. The hydrogen ends of the water molecules surround the cations and the oxygen ends

    surround the anions.

    Interpreting Graphics

     F. It forms a suspension of small particles.

     G. The crystal breaks apart into pairs of positive and negative ions.

     H. Ions separate from one another and interact with

     water molecules.

     I. The hydrogen ends of the water molecules surround the cations and the oxygen ends

    surround the anions.

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