writing formulas and naming compounds-2

8/3/2019 Writing Formulas and Naming Compounds-2

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Writing Names You can name a binary ionic compoundfrom its formula by using these rules.

1. Write the name of the positive ion.

2. Using Table 3, check to see if the positive ion is capable of

forming more than one oxidation number. If the ion has

only one possible oxidation number, proceed to step 3. If ithas more than one, determine the oxidation number of the

ion from the formula of the compound. To do this, keep in

mind that the overall charge of the compound is zero and

the negative ion has only one possible charge. Write the

charge of the positive ion using roman numerals in parentheses

after the ions name.

3. Write the root name of the negative ion. The root is the first part of the elements

name. For chlorine, the root is chlor-.4. Add the ending -ide to the root. Table 4 lists several elements and their-idecounterparts. For example, sulfur in a binary compound becomes sulfide. Subscripts do

not become part of the name for ionic compounds. However, subscripts can be used to

help determine the charges of these metals that have more than one positive charge.


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Writing Formulas To writeformulas for these compounds,

follow the rules for binary

compounds, with one addition.

When more than one polyatomic

ion is needed, write parenthesesaround the polyatomic ion before

adding the subscript.

How would you write the formula

of barium chlorate? First, identify

the symbol of the positive ion.

Barium has the symbol Ba and

forms a 2+ ion, Ba2+. Next, identifythe negative chlorate ion. Table 5

shows that it is ClO3-. Finally, you

need to balance the charges of theions to make the compound neutral.

It will take two chlorate ions with a

1- charge to balance the 2+ chargeof the barium ion. Because the

chlorate ion is polyatomic, you use

parentheses before adding the

subscript. The formula is Ba(ClO3)2.

Another example of naming complex compounds is shown in Figure 21.

Compounds with Added WaterSome ionic compounds have water molecules as part of their structure. These compounds

are called hydrates. A hydrate is a compound that has water chemically attached to its

ions and written into its chemical formula.

Common Hydrates The term hydrate comes from a word that means water. Whena solution of cobalt chloride evaporates, pink crystals that contain six water molecules for

each unit of cobalt chloride are formed. The formula for this compound is

CoCl2.H2O and is called cobalt chloride hexahydrate. You can remove water from thesecrystals by heating them. The resulting blue compound is called anhydrous, which means

without water. When anhydrous (blue) CoCl2is exposed to water, even from the air, it

will revert back to its hydrated state. The plaster of paris shown in Figure 22 also formsa hydrate when water is added. It becomes calcium sulfate dihydrate, which is also

known as gypsum. The water that was added to the powder became a part of the

compound.

To write the formula for a hydrate, write the formula for the compound and then place a

dot followed by the number of water molecules. The dot in the formula represents a ratio

of a compound to water molecules. For example, calcium sulfate dihydrate,


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CaSO4 . 2H2O, is the formula for the hydrate of calcium sulfate that contains twomolecules of water.

Naming Binary Covalent CompoundsCovalent compounds are those formed between elements that

are nonmetals. Some pairs of nonmetals can form more than

one compound with each other. For example, nitrogen and

oxygen can form N2O, NO, NO2 and N2O5. In the system you

have learned so far, each of these compounds would be called

nitrogen oxide. You would not know from that name what the

composition of the compound is.

Using Prefixes Scientists use the Greek prefixes in Table 6to indicate how many atoms of each element are in a binary

covalent compound. The nitrogen and oxygen compounds

N2O, NO, NO2, and N2O5 would be named dinitrogen oxide,

nitrogen oxide, nitrogen dioxide, and dinitrogen pentoxide.

Notice that the last vowel of the prefix is dropped when the

second element begins with a vowel, as in pentoxide. Often,

the prefix mono- is omitted, although it is used for emphasisin some cases. Carbon monoxide is one example.

Describing Chemical ReactionsChemical reactions are taking place all around you and even within you. A chemical

reaction is a change in which one or more substances are converted into new substances.

The substances that react are called reactants. The new substances produced are called

products.

Chemical and Nuclear Reactions When chemicalreactions occur, new compounds form when bonds between

atoms in the reactants break and new bonds form. Recall that

chemical bonds form when outer electrons, called valence

electrons, are shared between atoms or are transferred from

one atom to another. As a result, only the outer electrons of

atoms are involved in chemical reactions. The nucleus of an

atom is not affected by a chemical reaction. An atomic nucleus

changes only when nuclear decay or a nuclear reaction, such

as nuclear fission or fusion, occurs. The energy released by a

nuclear reaction is millions of times greater than the energy

released by a chemical reaction. Figure summarizes the

difference between nuclear and chemical reactions.


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Conservation of MassBy the 1770s, chemistry was changing from the art of alchemy to a true science. Instead

of being satisfied with a superficial explanation of unknown events, scientists began to

study chemical reactions more thoroughly. Through such study, the French chemist

Antoine Lavoisier established that the total mass of the products always equals the totalmass of the reactants.

The Father of Modern Chemistry When Lavoisier demonstrated the law ofconservation of mass, he set the field of chemistry on its modern path. In fact, Lavoisier

is known today as the father of modern chemistry.Lavoisiers Contribution One of the questions that motivated Lavoisier was themystery of exactly what happened when substances changed form. He began to answer

this question by experimenting with mercury. In one experiment, Lavoisier placed acarefully measured mass of solid mercury(II) oxide, which he knew as mercury calx, into

a sealed container. When he heated this container, he noted a dramatic change. The red

powder had been transformed into a silvery liquid that he recognized as mercury metal,

and a gas was produced. When he determined the mass of the liquid mercury and gas,

their combined masses were exactly the same as the mass of the red powder he had

started with.

Writing EquationsConsider the reaction:

Nickel(II) chloride, dissolved in water, plus sodium hydroxide, dissolved in water,

produces solid nickel(II) hydroxide plus sodium chloride, dissolved in water.

This series of words is rather cumbersome, but all of the information is important. The

same is true of descriptions of most chemical reactions.


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Many words are needed to state

all the important information. As a result, scientists have

developed a shorthand method to describe chemical

reactions. A chemical equation is a way to describe a

chemical reaction using chemical formulas and other

symbols. Some of the symbols used in chemicalequations are listed in Table 1.

The chemical equation for the reaction described above

in words looks like this:

On the left side of the equation are the reactants,

nickel(II) chloride and sodium hydroxide. On the right

side of the equation are the products, nickel(II)

hydroxide and sodium chloride.

Unit ManagersWhat do the numbers to the left of the formulas for

reactants and products mean? Remember that according

to the law of conservation of mass, matter is neither

made nor lost during chemical reactions. Atoms are

rearranged but never lost or destroyed. These numbers,

called coefficients, represent the number of units of each substance taking part in a

reaction. Coefficients can be thought of as unit managers.

Knowing the number of units of reactants enables chemists to add the correct amounts of

reactants to a reaction. Also, these units, or coefficients, tell them exactly how much

product will form. An example of this is the reaction of one unit of NiCl2 with two units

of NaOH to produce one unit of Ni(OH)2 and two units of NaCl. You can see these units

in Figure 5.


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Balanced EquationsLavoisiers mercury(II) oxide reaction, can be written as:

Notice that the number of mercury atoms is the same on both sides of the equation butthat the number of oxygen atoms is not the same. One oxygen atom appears on the

reactant side of the equation and two appear on the product side.

But according to the law of conservation of mass, one oxygen atom cannot just become

two. Nor can you simply add the subscript 2 and write HgO2instead of HgO. The

formulas HgO2 and HgO do not represent the same compound. In fact, HgO2 does not

exist. The formulas in a chemical equation must accurately represent the compounds that

react. Fixing this equation requires a process called balancing. Balancing an equation

doesnt change what happens in a reaction t simply changes the way the reaction is

represented. The balancing process involves changing coefficients in a reaction to

achieve a balanced chemical equation, which has the same number of atoms of each

element on both sides of the equation.

Choosing Coefficients Finding out which coefficients to use to balance an equationis often a trial-and-error process. In the equation for Lavoisiers experiment, the number

of mercury atoms is balanced, but one oxygen atom is on the left and two are on the right.

If you put a coefficient of 2 before the HgO on the left, the oxygen atoms will bebalanced, but the mercury atoms become unbalanced. To balance the equation, also put a

2 in front of mercury on the right. The equation is now balanced.

Balancing Equations Magnesium burns with such a brilliant white light that it isoften used in emergency flares. Burning leaves a white powder called magnesium

oxide. To write a balanced chemical equation for this and most other reactions, followthese four steps.

Step 1 Write a chemical equation for the reaction using formulas and symbols. Recall

that oxygen is a diatomic molecule.


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Step 3Choose coefficients that balance the equation. Remember, never change

subscripts of a correct formula to balance an equation. Try putting a coefficient of 2

before MgO.

Step 4Recheck the numbers of each atom on each side of the equation and adjust

coefficients again if necessary. Now two Mg atoms are on the right side and only one is

on the left side. So a coefficient of 2 is needed for Mg to balance the equation.


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Classifying Chemical Reactions

Types of ReactionsChemists have defined five main categories of chemical reactions: combustion, synthesis,

decomposition, single displacement, and double displacement.

Combustion Reactions If you have ever observed something burning, you haveobserved a combustion reaction. A combustion reaction occurs when a substance reacts

with oxygen to produce energy in the form of heat and light. Combustion reactions also

produce one or more products that contain the elements in the reactants. For example, the

reaction between carbon and oxygen produces carbon dioxide.

Many combustion reactions also will fit into other categories of reactions. For example,

the reaction between carbon and oxygen also is a synthesis reaction.

Synthesis Reactions One of the easiest reaction types to recognize is a synthesisreaction. In a synthesis reaction, two or more substances combine to form another

substance. The generalized formula for this reaction type is as follows:

The reaction in which hydrogen burns in oxygen to form water is an example of a

synthesis reaction. This reaction is used to power some types of rockets.

Another synthesis reaction is the combination of oxygen with iron in the presence ofwater to form hydrated iron(II) oxide or rust.

Decomposition Reactions A decomposition reaction isjust the reverse of a synthesis. Instead of two substances

coming together to form a third, a decomposition reaction

occurs when one substance breaks down, or decomposes,

into two or more

substances. The general formula for this type of reaction can

be expressed as follows:

Most decomposition reactions require the use of heat, light,

or electricity. An electric current passed through water

produces hydrogen and oxygen


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Single Displacement When one element replaces another element in a compound, itis called a single-displacement reaction. Single-displacement reactions are described by

the general equation . Here you can see that atom A displaces atom

B to produce a new molecule AC. Example of a single displacement reaction: a copper

wire is put into a solution of silver nitrate. Because copper is a more active metal than

silver, it replaces the silver, forming a blue copper(II) nitrate solution. The silver, whichis not soluble, forms on the wire.

The Activity Series Sometimes single-displacement reactions can cause

problems. For example, if iron-containing

vegetables such as spinach are cooked in

aluminum pans, aluminum can displace

iron from the vegetable. This causes ablack deposit of iron to form on the sides

of the pan. For this reason, it is better to

use stainless steel or enamel cookware

when cooking spinach.

We can predict which metal will replace

another using the diagram shown in

Figure, which lists metals according to how reactive they are. A metal can replace any

metal below it on the list but not above it. Notice that copper, silver, and gold are the

least active metals on the list. That is why these elements often occur as deposits of the

relatively pure element. For example, gold is sometimes found as veins in quartz rock.Copper is found in pure lumps known as native copper. Other metals can occur as

compounds.

Double Displacement In a double-displacement reaction, the positive ion of onecompound replaces the positive ion of the other to form two new compounds. A double-

displacement reaction takes place if a precipitate, water, or a gas forms when two ionic

compounds in solution are combined. A precipitate is an insoluble compound that comes

out of solution during this type of reaction. The generalized formula for this type of

reaction is as follows:

The reaction of barium nitrate with potassium sulfate is an example of this type ofreaction. A precipitatebarium sulfate forms,

Oxidation-Reduction Reactions One characteristic that is common to manychemical reactions is the tendency of the substances to lose or gain electrons. Chemists

use the term oxidation to describe the loss of electrons and the term reduction to


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describe the gain of electrons. Chemical reactions involving electron transfer of this sort

often involve oxygen, which is very reactive, pulling electrons from metallic elements.

Corrosion of metal is a visible result of this type of reaction. Reduction is the partner to

oxidation; the two always work as a pair, which is commonly referred to as redox.

Reaction Rates and EnergyAll chemical reactions release or absorb energy. This energy can take many forms, such

as heat, light, sound, or electricity. The heat produced by a wood fire and the light

emitted by a glow stick are two examples of reactions that release energy.

Conservation of Energy in Chemical ReactionsAccording to the law of conservation of energy, energy cannot be created or destroyed,

but can only change form. In compounds, chemical potential energy is stored in chemical

bonds between atoms. In some chemical reactions, chemical potential energy is changed

to other forms of energy, such as heat or light, and is released. In other chemicalreactions, forms of energy such as heat or light are converted to chemical potential

energy and stored in bonds that form, and energy is absorbed. In all chemical reactions,

energy is never created or destroyed, but only changes form. All reactions follow the laws

of conservation of mass and energy.

Activation EnergyAs you learned earlier, atoms and molecules have to bump into each other before a

product can be formed. In order to form new bonds, atoms have to be close together. In

addition to being close, the reactants require a certain amount of energy in order to allowthe reaction to start. This minimum amount of energy needed to start a reaction is called

activation energy.

Heat Absorption When the energy needed is in the form of heat, the reaction is calledan endothermic reaction. The term endothermicis not just related to chemicalreactions. It also can describe physical changes. The process of dissolving a salt in water

is a physical change. If you ever had to soak a swollen ankle in an Epsom salt solution,

you probably noticed that when you mixed the Epsom salt in water, the solution became

cold. The dissolving of Epsom salt absorbs heat. Thus, it is a physical change that is

endothermic. Some reactions are so endothermic that they can cause water to freeze.


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EndothermicReactions With anendothermic reaction, the

chemical reaction will not

take place unless energy is

added. A constant source of

energy must be added to

keep the reaction going.

The products have more

stored energy than the

reactants.

Figure shows an energydiagram for the reaction of

carbon dioxide (CO2) and nitrogen monoxide (NO). With an endothermic reaction, the

reactants have a lower energy level than the products. In order for the products to form,

an input of energy is needed for the reactants to overcome the activation energy barrier.

ExothermicReactions When theenergy given off in a

reaction is primarily in

the form of heat, the

reaction is called an

exothermic reaction.

The burning of wood andthe explosion of

dynamite are exothermic

reactions. Exothermic

reactions provide most of

the power used in homes

and industries. Fossil

fuels that contain carbon, such as coal, petroleum, and natural gas, combine with oxygen

to yield carbon dioxide gas and energy. Unfortunately impurities in these fuels, such as

sulfur, burn as well, producing pollutants such as sulfur dioxide. Sulfur dioxide combines

with water in the atmosphere, producing acid rain.Energy Release The energy diagram for an exothermic reaction is the reverse of anendothermic reaction. With an exothermic reaction, the products have less stored energy

than the reactants. As shown in Figure 21, the reactants, carbon monoxide (CO) andnitrogen dioxide (NO2) have a higher energy level than the products. The molecules have

enough energy to overcome the activation energy barrier.


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Chemical Reaction RatesAccording to the kinetic theory of matter, atoms and molecules are always moving. In

order for a chemical reaction to occur, the atoms and molecules that are the reactants

have to bump into each other or collide. The rate of reaction is the speed at which

reactants are consumed and products are produced in a given reaction.Reaction rate is important in the manufacturing industry because the faster the product

can be made, the less it usually costs. Sometimes a fast reaction rate is undesirable, such

as the rate of reaction that causes food spoilage. In this case, the slower the reaction

rate, the longer the food will stay edible.

What conditions control the reaction rate, and how can the rate be changed?

Temperature Energy is needed by atoms and molecules to break old bonds and toform new ones. One way to increase the activation energy is to add heat or increase the

temperature. With an increase in temperature, atoms and molecules move faster and

kinetic energy increases. With faster moving atoms and molecules, more molecules

have kinetic energy greater than activation energy. The atoms and molecules now will

have enough energy to break old bonds at higher temperature, which will increase the

reaction rate.

Concentration When you walk through the hallways at school, you are more likely tobump into another student if the hallways are crowded. The closer atoms and molecules

are to each other, the greater the chance of collision. The amount of substance present

in a certain volume is called its concentration. Increasing the concentration of a substance

increases the reaction rate.

Surface Area Only atoms or molecules in the outer layer of a substance can collidewith other reactants. When a substance is finely divided, it has a larger surface area than

when it was whole. Increasing the surface area increases the chance for collisions,

which will increase the reaction rate.

Agitation If you are making lemonade, the water, sugar, and lemon juice are mixed inorder to get the product. Agitation or stirring is a physical process that allows reactants to

mix. A low stirring rate will slow the reaction due to fewer collisions. Chemical reactions

can be controlled by agitation.

Pressure Another way to influence the reaction rate is with pressure. By increasing thepressure of gases, molecules have less room to move about and the concentration of the

reactants increases. This will boost the chance of collisions, which means the reaction

rate increases. Decreasing the pressure means fewer collisions, and lower reaction rate.


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Catalysts and Inhibitors Some reactions proceed too slowly to be useful. To speedthem up, a catalyst reaction can be added. A catalyst is substance that speeds up a

chemical reaction without being permanently changed itself. When you add a catalyst

to a reaction, the mass of the product that is formed remains the same, but it will form

more rapidly. At times, it is worthwhile to prevent certain reaction from occurring.

Substances that are used to slow down a chemical reaction are called inhibitors. Thefood preservations BHT and BHA are inhibitors that prevent spoilage of certain foods,

such as cereals and crackers.


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How Solutions Form

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

How Substances DissolveFruit drinks and sports drinks are examples of solutions made by dissolving solids in

liquids. Both contain sugar as well as other substances that add color and flavor. How do

solids such as sugar dissolve in water?

The dissolving of a solid in a liquid occurs at the surface of the solid. To understand howwater solutions form, keep in mind two things you have learned about water. Like the

particles of any substance, water molecules are constantly moving. Also, water molecules

are polar, which means they have a positive area and a negative area. Molecules of sugar

also are polar.

How It Happens Molecules of sugar dissolving in water are shown in Figure in thenext page. First, water molecules cluster around sugar molecules with their negative

ends attracted to the positive ends of the sugar. Then, the water molecules pull the sugar

molecules into solution. Finally, the water molecules and the sugar molecules mix

evenly, forming a solution.

The process described in Figure repeats as layer after layer of sugar molecules move

away from the crystal, until all the molecules are evenly spread out. The same three steps

occur for most solid solutes dissolving in a liquid solvent.


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Dissolving Liquids and Gases The sameprocess takes place when a gas dissolves in a

liquid. Particles of liquids and gases move much

more freely than do particles of solids. When

gases dissolve in gases or when liquids dissolve

in liquids, this movement spreads solutes evenlythroughout the solvent, resulting in a

homogenous solution.

Dissolving Solids in Solids How can youmix solids to make alloys? Although solid

particles do move a little, this movement is not

enough to spread them evenly throughout the

mixture. The solid metals are first melted and

then mixed together. In this liquid state, the metal

atoms can spread out evenly and will remain

mixed when cooled.

Rate of DissolvingWhen two substances form a solution, the

dissolving occurs at different rates. Sometimes

the rate at which a solute dissolves into a solvent

is fast, while other times it is slow. There are

several things you can do to speed up the rate of

dissolvingstirring, reducing crystal size, and

increasing temperature.

Stirring How does stirring speed up thedissolving process? Think about how you make a

drink from a powdered mix. After you add the

mix to water, you stir it. Stirring a solution

speeds up the dissolving process because it

brings more fresh solvent into contact with more

solute. The fresh solvent attracts the particles

of solute, causing the solid solute to dissolve

faster.

Crystal Size Another way to speed thedissolving of a solid in a liquid is to grind large

crystals into smaller ones. Suppose you

want to use a 5-g crystal of rock candy to

sweeten your water. If you put the whole crystal into a glass of water, it might take

several minutes to dissolve, even with stirring. However, if you first grind the crystal of

rock candy into a powder, it will dissolve in the same amount of water in a few seconds.


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Why does breaking up a solid cause it to dissolve faster? Breaking the solid into many

smaller pieces greatly increases its surface area, as you can see in Figure 5. Because

dissolving takes place at the surface of the solid, increasing the surface area allows more

solvent to come into contact with more solid solute. Therefore, the speed of the

dissolving process increases.

Temperature In addition to stirring and decreasing particle size, a third way toincrease the rate at which most solids dissolve is to increase the temperature of the

solvent. Think about making hot chocolate from a mix. You can make the sugar in the

chocolate mix dissolve faster by putting it in hot water instead of cold water. Increasing

the temperature of a solvent speeds up the movement of its particles. This increase causesmore solvent particles to bump into the solute. As a result, solute particles

break loose and dissolve faster.

Controlling the Process Think about how the three factors you just learned aboutaffect the rate of dissolving. Can these factors combine to further increase the rate, or

perhaps control the rate of dissolving? Each techniquestirring, crushing, and heating

is known to speed up the rate of dissolving by itself. However, when two or more

techniques are combined, the rate of dissolving is even faster. Consider a sugar cube

placed in cold water. You know that the sugar cube eventually will dissolve.

You can predict that heating the water will increase the rate by some amount. You also

can predict that heat and stirring will increase the rate further. Finally, you can predictthat crushing the cube combined with heating and stirring will result in the fastest rate of

dissolving. Knowing how much each technique affects the rate will allow you to control

the rate of dissolving more precisely.


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Types of SolutionsHow much solute can dissolve in a given amount of solvent? That depends on a number

of factors, including the solubility of the solute. Here you will examine the types of

solutions based on the amount of a solute dissolved.

Saturated Solutions If you add 35 g of copper(II) sulfate, CuSO4, to 100 g of waterat 20C, only 32 g will dissolve. You have a saturated solution because no more

copper(II) sulfate can dissolve. A saturated solution is a solution that contains all the

solute it can hold at a given temperature. However, if you heat the mixture to a higher

temperature, more copper(II) sulfate can dissolve. Generally, as the temperature of a

liquid solvent increases, the amount of solid solute that can dissolve in it also

increases. Table 2 shows the amounts of a few solutes that can dissolve in 100 g of water

at different temperatures to form saturated solutions.


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Unsaturated Solutions Anunsaturated solution is any solution that

can dissolve more solute at a given

temperature. Each time a saturated

solution is heated to a higher temperature,it generally becomes unsaturated. The term

unsaturatedisnt precise. If you look atTable 2, youll see that at 20C, 35.9 g of

NaCl (sodium chloride) forms a

saturated solution in 100 g of water.

However, an unsaturated solution of NaCl

could be any amount less than 35.9 g in

100 g of water at 20C.

Solubility of GasesWhen you shake an opened bottle of soda, it bubbles up and may squirt out. Shaking or

pouring a solution of a gas in a liquid causes gas to come out of solution. Agitating the

solution exposes more gas molecules to the surface, where they escape from the liquid.

Pressure Effects What might you do if you want to dissolve more gas in a liquid?One thing you can do is increase the pressure of that gas over the liquid. Soft drinks are

bottled under increased pressure. This increases the amount of carbon dioxide that

dissolves in the liquid. When the pressure is released, the carbon dioxide bubbles out.

Temperature Effects Another way to increase the amount of gas that dissolves in aliquid is to cool the liquid. This is just the opposite of what you do to increase the speed

at which most solids dissolve in a liquid. Imagine what happens to the carbon

dioxide when a bottle of soft drink is opened. Even more carbon dioxide will bubble out

of a soft drink as it gets warmer.


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AcidsProperties of Acids When an acid dissolves in water, some of the hydrogen isreleased as hydrogen ions, H_. An acid is a substance that produces hydrogen ions in a

water solution. It is the ability to produce these ions that gives acids their characteristic

properties. When an acid dissolves in water, H-ions interact with water molecules to form

H3O_ions, which are called hydronium ions.

Acids have several common properties. For one thing, all acids taste sour. The familiar,sour taste of many foods is due to acids. However, taste never should be used to test for

the presence of acids. Some acids can damage tissue by producing painful burns. Acids

are corrosive. Some acids react strongly with certain metals, eating away the metals and

forming metallic compounds and hydrogen gas. Acids also react with indicators


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to produce predictable changes in color. An indicator is an organic compound that

changes color in acids and bases. For example, the indicator litmus paper turns red in

acid.

Common Acids Many foods contain acids. In addition to citric acid in citrus fruits,lactic acid is found in yogurt and buttermilk, and food, such as pickles, contain vinegar,

also known as acetic acid. Your stomach uses acid to help digest your food. At least fouracids (sulfuric, phosphoric, nitric, and hydrochloric) play roles in industrial applications.


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BasesYou might not be as familiar with bases as you are with acids. Although you eat some

foods that are acidic, you dont consume many bases. Some foods, such as egg whites,

are slightly basic. Another example of basic materials is baking powder, which is

found in some foods. Medicines, such as milk of magnesia and antacids, are basic, too.Still, you come in contact with many bases every day. Each time you wash your hands

using soap, you are using a base. One characteristic of bases is that they feel slippery,

like soapy water.

Bases can be defined in two ways. Any substance that forms hydroxide ions, OH_, in

a water solution is a base. In addition, a base is any substance that accepts H_from

acids. The definitions are related, because the OH_ions produced by some bases

do accept H_ions.

Properties of BasesOne way to think about bases is as the complements, or

opposites, of acids. Although acids and bases share some common features, bases have

their own characteristic properties. In the pure, undissolved state, many bases are

crystalline solids. In solution, bases feel slippery and have a bitter taste. Like strong

acids, strong bases are corrosive, and contact with skin can result in severe burns. Taste

and touch never should be used to test for the presence of a base or an acid.

Finally, like acids, bases react with indicators to produce changes in color. The indicator

litmus turns blue in bases.


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Dissociation of Acids You have learned that substances such as HCl, HNO3, andH2SO4 are acids because of their ability to produce hydrogen ions (H+) in water. When an

acid dissolves in water, the negative areas of nearby water molecules attract the positive

hydrogen in the acid. The acid dissociates into ions and the hydrogen atom combines

with a water molecule to form hydronium ions (H3O+). Dissociation is the process in

which an ionic solid separates into its positive and negative ions. An acid can more

accurately be described as a compound that produces hydronium ions when dissolved in

water, as shown in above Figure.

Dissociation of Bases Compounds that can form hydroxide ions (OH) in water are

classified as bases. When bases that contain OH dissolve in water, the negative areas ofnearby water molecules attract the positive ion in the base. The positive areas of nearby

water molecules attract the OH of the base. The base dissociates into a positive ion and

a negative iona hydroxide ion (OH). This process also is shown in Figure.

Neutralization Advertisements for antacids claim that these products neutralize theexcess stomach acid that causes indigestion. Normally, gastric juice is acidic. Too much

acid can produce discomfort. Antacids contain bases or other compounds containing

sodium, calcium, magnesium, or aluminum that react with acids to lower acid

concentration. What happens when you ingest an antacid tablet containing sodium

bicarbonate, NaHCO3? The acid (HCl) is neutralized by the base (NaHCO3).

Neutralization is a chemical reaction between an acid and a base that takes place in a

water solution. When HCl is neutralized by NaOH, hydronium ions from the acid

combine with hydroxide ions from the base to produce water.


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Acid-Base Reactions The following general equation represent acid-base reactions

in water. A few common salts are listed in Table.

Salt Formation The acid-base equation accounts for only half of the ions in the

solution. The remaining ions react to form a salt. A salt is a compound formed when thenegative ions from an acid combine with the positive ions from a base. In the reaction

between HCl and NaOH, the salt formed in water solution is sodium chloride.

An Exception Ammonia is a base that does not containOH. In a water solution,dissociation takes place when the ammonia molecule attracts a hydrogen ion from a water

molecule, forming an ammonium ion (NH4+). This leaves a hydroxide ion (OH).

Ammonia (NH3) is a colourless pungent gas that is familiar to us as the smell of urine. In factprobably no other compound can be identified by its smell and correctly named by as many

people as ammonia. It can be detected in the air at a level of only about 50-60 ppm, and at levels

of 100-200 ppm it sharply irritates the eyes and lungs. At even higher concentrations it makes the

lungs fill with fluid and can quickly cause death. Ammonia takes it name from the worshippersof the Egyptian god Amun - the Ammonians, because they used ammonium chloride (NH4Cl) in

their rites. Ammonium chloride (also known assal volatile) occurs naturally in cracks nearvolcanoes, and when it is warmed it decomposes into the pungent ammonia.

The Haber Process

Industrially ammonia is made by theHaber-Bosch process which converts nitrogen gas into the

air into ammonia. This process was discovered by the German chemists Fritz Haber (nobel prize

1918) and Karl Bosch, just in time for the beginning of WW1. This had important consequences


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for the length of the war, since without this process Germany would not have been able to make

explosives (since it had no natural sources of nitrates from which explosives were made), and the

war might have ended much sooner than it did.

The Haber-Bosch Process - which takes place at 400-500C and about 200 atm pressure, in the

presence of an iron catalyst.

In the mid-1980s, the annual production rate for ammonia was about 16 million tons. About 25%

of this went directly for fertiliser, and the rest was used to make nitric acid (and from there intoexplosives), dyes, pharmaceuticals and cleaning agents. It has a relatively high heat of

vaporisation, and so some ammonia is used as the heat-exchanger gas in large refrigeration units

(rather than the ozone-destroying CFCs). With all of these important applications, it is nosurprise that more molecules of ammonia are produced each year than any other industrial

chemical.

writing formulas and naming compounds-2

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