Elements Compounds And Mixtures

• Think about pure water. No matter what Think about pure water. No matter what you do to it physically—freeze it, boil it, you do to it physically—freeze it, boil it, stir it, or strain it—it still is water.stir it, or strain it—it still is water.

• On the other hand, if you boil salt water, On the other hand, if you boil salt water, the water turns to gas and leaves the salt the water turns to gas and leaves the salt behind.behind.

• How does chemistry explain these How does chemistry explain these differences?differences?

SubstancesSubstancesWhat is a solution?What is a solution?What is a solution?What is a solution?

• Recall that atoms are the basic building Recall that atoms are the basic building blocks of matter. blocks of matter.

Atoms and ElementsAtoms and Elements

• A A substancesubstance is matter that has the same is matter that has the same fixed composition and properties. It can’t fixed composition and properties. It can’t be broken down into simpler parts by be broken down into simpler parts by ordinary physical processes, such as ordinary physical processes, such as boiling, grinding, or filtering. boiling, grinding, or filtering.

• Only a Only a chemical processchemical process can change a can change a substance into one or more new substance into one or more new substances. substances.


• AnAn element element is an example of a pure is an example of a pure substance; it cannot be broken down into substance; it cannot be broken down into simpler substances. simpler substances.

• The number of The number of protonsprotons in an in an elementelement, like , like oxygen, are fixed—it cannot change oxygen, are fixed—it cannot change unless the element changes. unless the element changes.


• Water is not an Water is not an elementelement. It is an example . It is an example of a of a compoundcompound which is made of two or which is made of two or more elements that are chemically more elements that are chemically combined. combined.

• CompoundsCompounds also have fixed also have fixed compositions. compositions.

CompoundsCompounds

• The ratio of the atoms in a The ratio of the atoms in a compoundcompound is is always the same. always the same.

• MixturesMixtures are are combinations of combinations of substances that substances that are not bonded are not bonded together and can together and can be separated by be separated by physical physical processes. processes.

MixturesMixtures

• Unlike compounds, mixtures do not always contain the same proportions of the substances that they are composed of.

Mixtures

MixturesMixtures

• Lemonade is a Lemonade is a mixture that can be mixture that can be strong tasting or strong tasting or weak tasting, weak tasting, depending on the depending on the amounts of water amounts of water and lemon juice and lemon juice that are added. that are added.

• A type of A type of mixture mixture where the where the substances are not substances are not mixed evenly is mixed evenly is called a called a heterogeneousheterogeneous (he (he tuh ruh JEE nee us) tuh ruh JEE nee us) mixturemixture..

• The different areas of a The different areas of a heterogeneous heterogeneous mixturemixture have different compositions. have different compositions.

Heterogeneous MixturesHeterogeneous Mixtures

Heterogeneous MixturesHeterogeneous Mixtures

• The substances in a The substances in a heterogeneousheterogeneous mixturemixture are usually are usually easy to tell apart, like easy to tell apart, like the seeds from the the seeds from the fruit of a fruit of a watermelon. watermelon.

• A A homogeneous mixturehomogeneous mixture contains two or contains two or more substances that are evenly mixed on more substances that are evenly mixed on a molecular level but still are not bonded a molecular level but still are not bonded together.together.

• Another name for a Another name for a homogeneoushomogeneous mixturemixture is a is a solutionsolution..

Homogeneous MixturesHomogeneous Mixtures

• The substance that dissolves—or seems to The substance that dissolves—or seems to disappear—is called the disappear—is called the solutesolute..

• The substance that The substance that dissolves the dissolves the solutesolute is is called the called the solventsolvent..

How Solutions FormHow Solutions Form

How Solutions FormHow Solutions Form

• In a hummingbird In a hummingbird feeder feeder solutionsolution, the , the solutesolute is the sugar and is the sugar and the the solventsolvent is water. is water.

• Under certain conditions, a Under certain conditions, a solutesolute can can come back out of its come back out of its solutionsolution and form a and form a solid. solid.

• This process is called This process is called crystallizationcrystallization. .

Forming Solids from SolutionsForming Solids from Solutions

• CrystallizationCrystallization is the result of a physical is the result of a physical change. change.

• When some When some solutionssolutions are mixed, a are mixed, a chemical reaction occurs, forming a solid. chemical reaction occurs, forming a solid. This solid is called a This solid is called a precipitateprecipitate (prih (prih SIH puh tayt). SIH puh tayt).

• A A precipitateprecipitate is the result of a chemical is the result of a chemical change. change.


• StalactitesStalactites and and stalagmitesstalagmites in caves are in caves are formed from formed from solutions.solutions.

• First, minerals dissolve in water as it First, minerals dissolve in water as it flows through rocks at the top of the cave.flows through rocks at the top of the cave.


• This This solutionsolution of water and dissolved of water and dissolved minerals drips from the ceiling of the minerals drips from the ceiling of the cave.cave.

• When drops of the When drops of the solutionsolution evaporate from evaporate from the roof of the cave, the minerals are left the roof of the cave, the minerals are left behind. behind.

• They create the hanging They create the hanging rock formations called rock formations called stalactitesstalactites..


StalactiteStalactite


• When drops of the solution fall onto the floor of the cave and evaporate, they form stalagmites.

StalagmiteStalagmite

Types of SolutionsTypes of Solutions

• SolutionsSolutions can be made up of different can be made up of different combinations of solids, liquids, and gases.combinations of solids, liquids, and gases.

• You’ve already learned about liquid-solid solutions such as sugar water and salt water.

• When discussing solutions, the state of the solvent usually determines the state of the solution.

Liquid SolutionsLiquid Solutions

• Carbonated beverages are liquid-gas Carbonated beverages are liquid-gas solutionssolutions—carbon dioxide is the gaseous —carbon dioxide is the gaseous solutesolute, and water is the liquid solvent., and water is the liquid solvent.

• The carbon dioxide gas The carbon dioxide gas gives the beverage its fizz gives the beverage its fizz and some of its tartness. and some of its tartness.

Liquid-Gas SolutionsLiquid-Gas Solutions

• In a liquid-liquid In a liquid-liquid solutionsolution, both the solvent , both the solvent and the and the solutesolute are liquids. are liquids.

• Vinegar, which you might use to make salad dressing, is a liquid-liquid solution made of 95 percent water (the solventthe solvent) and 5 percent acetic acid (the solute).

Liquid-Liquid SolutionsLiquid-Liquid Solutions

• In In gaseous solutionsgaseous solutions, a smaller amount of , a smaller amount of one gas is dissolved in a larger amount of one gas is dissolved in a larger amount of another gas. another gas.

• This is called a gas-gas This is called a gas-gas solutionsolution because because both the both the solvent solvent and and solutesolute are gases. are gases.

Gaseous SolutionsGaseous Solutions

• The air you breathe is a The air you breathe is a gaseous solutiongaseous solution. .

• In In solid solutionssolid solutions, the , the solventsolvent is a solid. is a solid.

• The The solutesolute can be a solid, liquid, or gas. can be a solid, liquid, or gas.

Solid SolutionsSolid Solutions

• The most common The most common solid solutionssolid solutions are are solid-solid solutions—ones in which the solid-solid solutions—ones in which the solvent solvent and the and the solutesolute are solids. are solids.

• A solid-solid A solid-solid solutionsolution made from two or made from two or more more metalsmetals is called an is called an alloyalloy. .

Solid Solutions

• Brass is a Brass is a solid solutionsolid solution made of copper made of copper and zinc. and zinc.

Water—The Universal SolventWater—The Universal Solvent

• A A solutionsolution in which water is the in which water is the solventsolvent is called an is called an aqueousaqueous (A kwee (A kwee us) us) solutionsolution. .

• Because water can dissolve so many Because water can dissolve so many different different solutessolutes, chemists often call it the , chemists often call it the universal solventuniversal solvent. .

Molecular CompoundsCompounds

• When certain atoms form When certain atoms form compoundscompounds, , they share electrons. Sharing electrons is they share electrons. Sharing electrons is called called covalent bondingcovalent bonding. .

• CompoundsCompounds that that contain contain covalentcovalent bondsbonds are called are called molecular molecular compoundscompounds, or , or moleculesmolecules. .

Molecular CompoundsMolecular Compounds• If a molecule has an even distribution of

electrons it is called nonpolar.

• In a water molecule, the electrons spend more time around the oxygen atom than the hydrogen atoms.

• Such a molecule is polar.

IonicIonic Bonds

• Atoms with a charge are called Atoms with a charge are called ionsions. .

• Bonds between Bonds between ionsions that are formed by that are formed by the transfer of electrons are called the transfer of electrons are called ionicionic bondsbonds, and the , and the compound compound that is formed that is formed is called an is called an ionic compoundionic compound. .

• Table salt is an Table salt is an ionic compoundionic compound that is that is made of made of sodium ionssodium ions and and chloride ionschloride ions. .

How Water Dissolves Ionic CompoundsHow Water Dissolves Ionic Compounds

• Because water Because water moleculesmolecules are are polarpolar, they , they attract attract positivepositive and and negative ionsnegative ions. .

• The more positive part of a water The more positive part of a water molecule—where the hydrogen atoms aremolecule—where the hydrogen atoms are—is attracted to negatively charged ions. —is attracted to negatively charged ions.


• The more negative part of a water The more negative part of a water molecule—where the oxygen atom is—molecule—where the oxygen atom is—attracts attracts positive ionspositive ions. .

• When an When an ionic compoundionic compound is mixed with is mixed with water, the different ions of the compound water, the different ions of the compound are pulled apart by the water molecules. are pulled apart by the water molecules.

How Water Dissolves Molecular How Water Dissolves Molecular CompoundsCompounds

• Water does dissolve Water does dissolve molecularmolecular compoundscompounds, such as sugar, although it , such as sugar, although it doesn’t break each sugar molecule apart. doesn’t break each sugar molecule apart.

• Water simply Water simply moves between moves between different molecules different molecules of sugar, separating of sugar, separating them. them.

What will dissolve?What will dissolve?

• When you stir a spoonful of sugar into iced tea, all of the sugar dissolves but none of the metal in the spoon does.

• A substance that dissolves in another is said to be soluble in that substance.

• You would say that the sugar is soluble in water but the metal of the spoon is insoluble in water.

Like Dissolves LikeLike Dissolves Like

• When trying to predict which When trying to predict which solventssolvents can can dissolvedissolve which which solutessolutes, chemists use the , chemists use the rule of “rule of “like dissolves likelike dissolves like.” .”

• Polar solvents dissolve polar solutes and Polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar nonpolar solvents dissolve nonpolar solutes. solutes.

Like Dissolves LikeLike Dissolves Like

• On the other hand, if a On the other hand, if a solventsolvent and a and a solute are not similar, the solute won’t solute are not similar, the solute won’t dissolve. dissolve.

• For example, oil and water do not mix.For example, oil and water do not mix.

• Oil molecules are Oil molecules are nonpolanonpolar, so r, so polarpolar water moleculeswater molecules are not attracted to are not attracted to them. them.

How much will dissolve?• Solubility (sahl yuh BIH luh tee) is a

measurement that describes how much solute dissolves in a given amount of solvent.

• The solubility of a material has been described as the amount of the material that can dissolve in 100 g of solvent at a given temperature.

• When a substance has an extremely low solubility, it usually is considered insoluble.

Solubility in Liquid-Solid SolutionsSolubility in Liquid-Solid Solutions

• The The solubilitysolubility of many of many solutessolutes changes if changes if you change the you change the temperature of the temperature of the solvent. solvent.

• For example, if you heat water, not only For example, if you heat water, not only does the sugar does the sugar dissolve at a faster ratedissolve at a faster rate, but , but more sugar can dissolve in itmore sugar can dissolve in it. .

• This graph shows how the temperature of the solvent affects the solubility of some solutes.

Solubility in Liquid-Gas SolutionsSolubility in Liquid-Gas Solutions

• Unlike Unlike liquid-solid solutionsliquid-solid solutions, an increase , an increase in temperature decreases the in temperature decreases the solubility solubility of of a gas in a liquid-gas solution. a gas in a liquid-gas solution.

• You might notice this if you have ever You might notice this if you have ever opened a warm carbonated beverage and opened a warm carbonated beverage and it bubbled up out of control while a it bubbled up out of control while a chilled one barely fizzed. chilled one barely fizzed.

• Carbon dioxide is Carbon dioxide is less solubleless soluble in a in a warm warm solutionsolution. .

Saturated SolutionsSaturated Solutions

• A A solutionsolution that contains all of the that contains all of the solutesolute that it can hold under the given conditions that it can hold under the given conditions is called a is called a saturatedsaturated solution. solution.

• If a If a solutionsolution is a is a liquid-solid solutionliquid-solid solution, the , the extra extra solutesolute that is added will settle to the that is added will settle to the bottom of the container.bottom of the container.

• It’s possible to make It’s possible to make solutionssolutions that have that have less less solutesolute than they would need to than they would need to become become saturatedsaturated. Such . Such solutionssolutions are are unsaturatedunsaturated. .

Saturated SolutionsSaturated Solutions

• A hot solvent usually can hold more solute than a cool solvent can.

• If a saturated solution is cooled slowly, sometimes the excess solute remains dissolved for a period of time.

• Such a solution is said to be supersaturated, because it contains more than the normal amount of solute.

Rate of DissolvingRate of Dissolving

• Some Some solutes dissolvesolutes dissolve quickly, but others quickly, but others take a long time to take a long time to dissolvedissolve. .

• A A solute dissolvessolute dissolves faster faster when the when the solutionsolution is stirred is stirred or shaken or when the or shaken or when the temperature of the temperature of the solutionsolution is increased.is increased.

Rate of DissolvingRate of Dissolving

• These methods These methods increase the rate at increase the rate at which the surfaces of which the surfaces of the the solutesolute come into come into contact with the contact with the solventsolvent. .

ConcentrationConcentration

• The The concentrationconcentration of a solution tells you of a solution tells you how much how much solutesolute is present compared to is present compared to the amount of the amount of solventsolvent. .

• You can give a simple description of a You can give a simple description of a solution’s solution’s concentrationconcentration by calling it by calling it either either concentratedconcentrated or or dilutedilute. .

• A A concentrated solutionconcentrated solution has more has more solutesolute per given amount of per given amount of solventsolvent than a than a dilutedilute solutionsolution. .

MeasuringMeasuring Concentrations

• One way of giving the exact One way of giving the exact concentrationconcentration is to state the is to state the percentage of the volume of the percentage of the volume of the solutionsolution that is made up of that is made up of solutesolute. .

Measuring ConcentrationsMeasuring Concentrations

• Labels on fruit drinks show their Labels on fruit drinks show their concentrationconcentration. .

• Another way to Another way to describe the describe the concentrationconcentration of a of a solution is to give solution is to give a percentage of a percentage of the total mass that the total mass that is made up of is made up of solute.solute.

Effects of Solute ParticlesEffects of Solute Particles

• The effect that a solute has on the The effect that a solute has on the freezing or boiling point of a solvent freezing or boiling point of a solvent depends on the number of depends on the number of solute particlessolute particles. .

• When a solvent such as water begins to When a solvent such as water begins to freeze, its molecules arrange themselves freeze, its molecules arrange themselves in a particular pattern. in a particular pattern.

Effects of Solute ParticlesEffects of Solute Particles

• Adding a solute such as sodium chloride to this solvent changes the way the molecules arrange themselves.

• To overcome this interference of the solute, a lower temperature is needed to freeze the solvent.

AcidsAcids

• AcidsAcids are substances that release are substances that release positively charged positively charged hydrogen ions, Hhydrogen ions, H++,, in in the water.the water.

• When an When an acidacid mixes with water, the mixes with water, the acidacid dissolves, releasing a dissolves, releasing a hydrogen ionhydrogen ion..

Acidic and Basic SolutionsAcidic and Basic SolutionsAcidic and Basic SolutionsAcidic and Basic Solutions

AcidsAcids

• The The hydrogen ionhydrogen ion then combines with a then combines with a water molecule to form a water molecule to form a hydronium ionhydronium ion. .

• Hydronium ionsHydronium ions are positively charged are positively charged and have the formula and have the formula HH33OO++..

Properties of Acidic SolutionsProperties of Acidic Solutions• Sour tasteSour taste is one of the is one of the properties of properties of

acidic solutions. acidic solutions. • Another Another property of acidic solutionsproperty of acidic solutions is is

that they can that they can conduct electricityconduct electricity..

• Acidic solutionsAcidic solutions also are also are corrosivecorrosive, which , which means they break down certain means they break down certain substances. Many acids can corrode substances. Many acids can corrode fabric, skin, and paper. fabric, skin, and paper.

• The The solutions of some acidssolutions of some acids also react also react strongly with strongly with certain metalscertain metals. .

Uses of AcidsUses of Acids

• Vinegar, which is used in salad dressing, contains acetic acid.

• Lemons, limes, and oranges have a sour taste because they contain citric acid.


• Your body needs Your body needs ascorbic acidascorbic acid, which is , which is vitamin Cvitamin C..

• Sulfuric acidSulfuric acid is used in is used in the production of the production of fertilizers, steel, paints, fertilizers, steel, paints, and plastics. and plastics.


• AcidsAcids often are used in batteries because often are used in batteries because their their solutions conduct electricitysolutions conduct electricity..

• Hydrochloric acidHydrochloric acid, which is known , which is known commercially as commercially as muriatic acidmuriatic acid, is used in , is used in a process called pickling. a process called pickling. PicklingPickling is a is a process that removes impurities from the process that removes impurities from the surfaces of metals. surfaces of metals.

Acid in the EnvironmentAcid in the Environment

• Carbonic acidCarbonic acid plays a key role in the plays a key role in the formation of caves and of formation of caves and of stalactitesstalactites and and stalagmitesstalagmites. .

• Carbonic acidCarbonic acid is formed when carbon is formed when carbon dioxide in soil is dissolved in water. dioxide in soil is dissolved in water.

• When this When this acidic solutionacidic solution comes in comes in contact with calcium carbonate—or contact with calcium carbonate—or limestone rock—it can dissolve it, limestone rock—it can dissolve it, eventually carving out a cave in the rock.eventually carving out a cave in the rock.

BasesBases

• BasesBases are substances that can accept are substances that can accept hydrogen ionshydrogen ions. .

• When When basesbases dissolve in water, some dissolve in water, some hydrogen atomshydrogen atoms from the water molecules from the water molecules are attracted to the are attracted to the basebase. .

BasesBases• A hydrogen atom in the water molecule A hydrogen atom in the water molecule

leaves behind the other hydrogen atom leaves behind the other hydrogen atom and oxygen atom. and oxygen atom.

• This pair of atoms is a This pair of atoms is a negatively chargednegatively charged ionion called a called a hydroxide ionhydroxide ion. .

• A A hydroxide ionhydroxide ion has the has the formula OHformula OH––..

• Most Most basesbases contain a contain a hydroxide ionhydroxide ion, , which is released when the base dissolves which is released when the base dissolves in water. in water.

Properties of Basic SolutionsProperties of Basic Solutions

• Basic solutions feel slippery.

• Bases also taste bitter.

• Like acids, bases are corrosive.

• Basic solutions contain ions and can conduct electricity. Basic solutions are not as reactive with metals as acidic solutions are.

Uses of BasesUses of Bases• BasesBases give soaps, ammonia, and many give soaps, ammonia, and many

other cleaning products some of their other cleaning products some of their useful properties. useful properties.

• The The hydroxide ionshydroxide ions produced by bases produced by bases can interact strongly with certain can interact strongly with certain substances, such as dirt and grease. substances, such as dirt and grease.

Uses of BasesUses of Bases

• Chalk and oven cleaner are examples of Chalk and oven cleaner are examples of familiar products that contain bases.familiar products that contain bases.

• Your blood is a basic solution. Your blood is a basic solution.

Click box to view movie.

What is pH?What is pH?

• pHpH is a is a measuremeasure of how of how acidic or basicacidic or basic a a solution is. solution is.

• The The pH scalepH scale ranges from ranges from 0 to 140 to 14. .

• Acidic solutionsAcidic solutions have have pH values below 7pH values below 7. .

• A solution with a pH of 0 is very acidic.

• A solution with a pH of 7 is neutral.

• Basic solutions have pH values above 7.

pH ScalepH Scale• A A change of 1 pHchange of 1 pH unit represents a unit represents a

tenfold changetenfold change in the in the acidityacidity of the of the solution. solution.

• For example, if one solution has a For example, if one solution has a pH of 1pH of 1 and a second solution has a and a second solution has a pH of 2pH of 2, the , the first solution is not twice as acidicfirst solution is not twice as acidic as the as the second—it is second—it is ten times more acidicten times more acidic. .

Strengths of Acids and BasesStrengths of Acids and Bases

• The difference between food acids and the acids that can burn you is that they have different strengths.

• The strength of an acid is related to how easily the acid separates into ions, or how easily a hydrogen ion is released, when the acid dissolves in water.

Strengths of Acids and BasesStrengths of Acids and Bases• In the same concentration, a strong acid—In the same concentration, a strong acid—

like hydrochloric acid—forms more like hydrochloric acid—forms more hydronium ions in solution than a weak hydronium ions in solution than a weak acid does—like acetic acid. acid does—like acetic acid.

Strengths of Acids and BasesStrengths of Acids and Bases

• More More hydronium ionshydronium ions means the means the strong-strong-acid solutionsacid solutions has a has a lower pHlower pH than the than the weak-acid solutionweak-acid solution. .

Strengths of Acids and BasesStrengths of Acids and Bases• The The strength of a basestrength of a base is related to how is related to how

easily the base easily the base separates into ionsseparates into ions, or how , or how easily a easily a hydroxide ion is releasedhydroxide ion is released, when , when the the base dissolves in waterbase dissolves in water. .

IndicatorsIndicators• IndicatorsIndicators are compounds that react with are compounds that react with

acidic and basic solutions and produce acidic and basic solutions and produce certain colors, depending on the certain colors, depending on the solution’s pH. solution’s pH.

• Because they are different colors at Because they are different colors at different pHs, indicators can help you different pHs, indicators can help you determine the pH of a solution. determine the pH of a solution.

• When When litmus paperlitmus paper is placed in an is placed in an acidicacidic solutionsolution, it , it turns redturns red. When placed in a . When placed in a basic solution, litmus paper turns bluebasic solution, litmus paper turns blue..

NeutralizationNeutralization• Heartburn or stomach discomfort is Heartburn or stomach discomfort is

caused by caused by excess hydrochloric acidexcess hydrochloric acid in the in the stomach. stomach.

• An antacid product, often made from the An antacid product, often made from the base base magnesium hydroxide, Mg(OH)magnesium hydroxide, Mg(OH)

22, , neutralizesneutralizes the excess acid. the excess acid.

• NeutralizationNeutralization (new truh luh ZAY shun) (new truh luh ZAY shun) is the reaction of an acid with a base. It is is the reaction of an acid with a base. It is called this because the properties of both called this because the properties of both the acid and base are diminished, or the acid and base are diminished, or neutralizedneutralized. .

How does neutralization occur?How does neutralization occur?

• Recall that every water molecule contains Recall that every water molecule contains two hydrogen atomstwo hydrogen atoms and and one oxygenone oxygen atomatom. .

• When When one hydronium ionone hydronium ion reacts with reacts with oneone hydroxide ionhydroxide ion, the product is , the product is two watertwo water moleculesmolecules. This reaction occurs during . This reaction occurs during acid-base neutralizationacid-base neutralization. .

How does neutralization occur?How does neutralization occur?

• Equal numbers of hydronium ions from the acidic solution and hydroxide ions from the basic solution react to produce water.

• Pure water has a pH of 7, which means that it’s neutral.

Elements Compounds And Mixtures

Technology

Transcript of Elements Compounds And Mixtures