Chapter: Substances, Mixtures, and Solubility

Chapter: Substances, Mixtures, and Solubility

Table of ContentsTable of Contents

Section 3: Acidic and Basic Solutions

Section 1: What is a solution?

Section 2: Solubility

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

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

• How does chemistry explain these differences?

SubstancesWhat is a solution?What is a solution?

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

Atoms and ElementsWhat is a solution?What is a solution?

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Click image to view movie.

• A substance is matter that has the same fixed composition and properties. It can’t be broken down into simpler parts by ordinary physical processes, such as boiling, grinding, or filtering. • Only a chemical process can change a substance into one or more new substances.


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

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


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

• Compounds also have fixed compositions.

CompoundsWhat is a solution?What is a solution?

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

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

MixturesWhat is a solution?What is a solution?

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


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

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

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

Heterogeneous MixturesWhat is a solution?What is a solution?

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Heterogeneous MixturesWhat is a solution?What is a solution?

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

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

• Another name for a homogeneous mixture is a solution.

Homogeneous MixturesWhat is a solution?What is a solution?

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

• The substance that dissolves the solute is called the solvent.

How Solutions FormWhat is a solution?What is a solution?

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How Solutions FormWhat is a solution?What is a solution?

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• In a hummingbird feeder solution, the solute is the sugar and the solvent is water.

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

• This process is called crystallization.

Forming Solids from SolutionsWhat is a solution?What is a solution?

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• Crystallization is the result of a physical change.

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

• A precipitate is the result of a chemical change.

• Stalactites and stalagmites in caves are formed from solutions.

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


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

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

• They create the hanging rock formations called stalactites.


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Stalactite


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

Stalactite

Types of SolutionsWhat is a solution?What is a solution?

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• Solutions can be made up of different combinations of solids, liquids, and gases, as shown in this table.

• 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 SolutionsWhat is a solution?What is a solution?

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• Carbonated beverages are liquid-gas solutions—carbon dioxide is the gaseous solute, and water is the liquid solvent.• The carbon dioxide gas gives the beverage its fizz and some of its tartness.

Liquid-Gas SolutionsWhat is a solution?What is a solution?

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• In a liquid-liquid solution, both the solvent and the solute are liquids.

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

Liquid-Liquid SolutionsWhat is a solution?What is a solution?

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

• This is called a gas-gas solution because both the solvent and solute are gases.

Gaseous SolutionsWhat is a solution?What is a solution?

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• The air you breathe is a gaseous solution.

• In solid solutions, the solvent is a solid.

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

Solid SolutionsWhat is a solution?What is a solution?

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

• A solid-solid solution made from two or more metals is called an alloy.

Solid SolutionsWhat is a solution?What is a solution?

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

11Section CheckSection Check

Question 1Which of the processes in the table results in a new substance?

A. boilingB. coolingC. reacting with lightD. sorting


AnswerThe answer is C. Only a chemical process can change one substance into a new substance.


Question 2In a solution, the substance that dissolves is called the _______.

A. precipitateB. soluteC. solventD. solution


AnswerThe answer is B. The substance that dissolves the solute is the solvent.


Question 3Sometimes a solute can come out of its solution once more and form a solid. This process is known as _______.

AnswerThe answer is crystallization. This can occur when the solution cools, or when some of the solvent evaporates.

Water—The Universal Solvent

• A solution in which water is the solvent is called an aqueous (A kwee us) solution.

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

SolubilitySolubility22

Molecular Compounds

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

• Compounds that contain covalent bonds are called molecular compounds, or molecules.


Molecular 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.

Ionic Bonds• Atoms with a charge are called ions.

• Bonds between ions that are formed by the transfer of electrons are called ionic bonds, and the compound that is formed is called and ionic compound.


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

How Water Dissolves Ionic Compounds

• Because water molecules are polar, they attract positive and negative ions.


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




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


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

How Water Dissolves Molecular Compounds

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


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

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 Like

• When trying to predict which solvents can dissolve which solutes, chemists use the rule of “like dissolves like.”


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

Like Dissolves Like• On the other hand, if a solvent and a solute

are not similar, the solute won’t dissolve.


• For example, oil and water do not mix.

• Oil molecules are nonpolar, so polar water molecules are not attracted to 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 Solutions

• The solubility of many solutes changes if you change the temperature of the solvent.


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

Solubility in Liquid-Solid SolutionsSolubilitySolubility

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

Solubility in Liquid-Gas Solutions• Unlike liquid-solid solutions, an increase

in temperature decreases the solubility of a gas in a liquid-gas solution.


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

• Carbon dioxide is less soluble in a warm solution.

Saturated Solutions• A solution that contains all of the solute

that it can hold under the given conditions is called a saturated solution.


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

• It’s possible to make solutions that have less solute than they would need to become saturated. Such solutions are unsaturated.

Saturated 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 Dissolving• Some solutes dissolve

quickly, but others take a long time to dissolve.


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

Rate of DissolvingSolubilitySolubility

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• These methods increase the rate at which the surfaces of the solute come into contact with the solvent.

Concentration• The concentration of a solution tells you

how much solute is present compared to the amount of solvent.


• You can give a simple description of a solution’s concentration by calling it either concentrated or dilute.

• A concentrated solution has more solute per given amount of solvent than a dilute solution.

Measuring Concentrations• One way of giving the exact concentration

is to state the percentage of the volume of the solution that is made up of solute.


Measuring ConcentrationsSolubilitySolubility

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• Labels on fruit drinks show their concentration.

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

Effects of Solute Particles

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


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

Effects 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.


Question 1Bonds between ions formed by the transfer of electrons are known as _______.

The answer is ionic bonds. “Ions” are atoms with a net charge, either positive or negative.

Answer


Question 2How does water dissolve ionic compounds?

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

Answer


Question 3The measure of how much solute will dissolve in a given amount of solvent is its _______.

The answer is solubility. If you have ever stirred too much sugar into a glass of water and had some left on the bottom, you have observed solubility.

Answer

Acids

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

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

Acidic and Basic SolutionsAcidic and Basic Solutions

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Acids• The hydrogen ion then combines with a

water molecule to form a hydronium ion. • Hydronium ions are positively charged

and have the formula H3O+.


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Properties of Acidic Solutions• Sour taste is one of the properties of acidic

solutions. • Another property of acidic solutions is that

they can conduct electricity.


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• Acidic solutions also are corrosive, which means they break down certain substances. Many acids can corrode fabric, skin, and paper. • The solutions of some acids also react strongly with certain metals.

Uses 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.


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Uses of AcidsAcidic and Basic SolutionsAcidic and Basic Solutions

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

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

Uses of Acids

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

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


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Acid in the Environment• Carbonic acid plays a key role in the

formation of caves and of stalactites and stalagmites.

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


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

Bases

• Bases are substances that can accept hydrogen ions.

• When bases dissolve in water, some hydrogen atoms from the water molecules are attracted to the base.


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Bases• A hydrogen atom in the water molecule

leaves behind the other hydrogen atom and oxygen atom.

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


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• A hydroxide ion has the formula OH–. • Most bases contain a hydroxide ion, which

is released when the base dissolves in water.

Properties of Basic Solutions• Basic solutions feel slippery.

• Bases also taste bitter.


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• 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 Bases• Bases give soaps, ammonia, and many

other cleaning products some of their useful properties.


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

Uses of Bases• Chalk and oven

cleaner are examples of familiar products that contain bases.


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• Your blood is a basic solution. Click box to view movie.

What is pH?• pH is a measure of how acidic or basic a

solution is.


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• The pH scale ranges from 0 to 14. • Acidic solutions have pH 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 Scale• A change of 1 pH unit represents a tenfold

change in the acidity of the solution.


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

Strengths of Acids and Bases

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


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• 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 Bases• In the same concentration, a strong acid—

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


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Strengths of Acids and Bases• More hydronium ions means the strong-

acid solutions has a lower pH than the weak-acid solution.


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Strengths of Acids and BasesAcidic and Basic SolutionsAcidic and Basic Solutions

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

Indicators• Indicators are compounds that react with

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


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

• When litmus paper is placed in an acidic solution, it turns red. When placed in a basic solution, litmus paper turns blue.

Neutralization• Heartburn or stomach discomfort is caused

by excess hydrochloric acid in the stomach.


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• An antacid product, often made from the base magnesium hydroxide, Mg(OH)2, neutralizes the excess acid. • Neutralization (new truh luh ZAY shun) is the reaction of an acid with a base. It is called this because the properties of both the acid and base are diminished, or neutralized.

How does neutralization occur?

• Recall that every water molecule contains two hydrogen atoms and one oxygen atom.


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How does neutralization occur?Acidic and Basic SolutionsAcidic and Basic Solutions

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• When one hydronium ion reacts with one hydroxide ion, the product is two water molecules. This reaction occurs during acid-base neutralization.

How does neutralization occur?

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


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

Section CheckSection Check

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Which contains acid?

A. ammoniaB. chalkC. lyeD. orange

Question 1


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The answer is D. Oranges contain citric acid.

Answer


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Substances that can accept hydrogen ions are known as _______.

Question 2

The answer is bases. Ammonia is a common example of a base.

Answer


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Explain how acid rain forms and why it is a serious concern.

Question 3


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Fossil-fuel burning systems, such as cars, give off sulfur dioxide and nitrogen oxide into the atmosphere. These react with water vapor to form acidic solutions of nitric acid and sulfuric acid. These solutions eventually return to Earth as acid precipitation which can damage forests and corrode stone.

Answer

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Chapter: Substances, Mixtures, and Solubility