Chemistry - an illustrated guide to science (794128), страница 22
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For example, copper(II) sulfate isformed by the reaction of copper(II)oxide and sulfuric acid.● An excess of copper(II) oxide is usedto ensure that all of the sulfuric acidhas reacted and no acid residueremains. The excess is filtered off,leaving a blue solution of copper(II)sulfate.● Copper(II) sulfate crystals are obtainedby boiling off some of the water fromthe copper(II) sulfate solution andallowing the remaining solution tocool.hAdd the base todilute acidjhWarm gently, addingthe base until nomore will dissolveFilter off excesssolid and collectthe filtratehEvaporate off filtratea buretteb acidc alkali and phenolphthalein indicatorAdd the acid until the solution just turnscolorless.d volume of acid in the burette before carryingout the proceduree volume of acid remaining when the indicatorhas turned colorlessf salt solutiong boiling waterh heati neutralized acidj excess solid127Proton transfer:neutralization of alkalisCHEMICAL REACTIONSKey wordsammoniumhydroxideammonium ionhydronium ionhydroxide ion1 Water particlesHHHHOOH1 Water particlesO● Ina water molecule, the oxygen atomforms bonds with two hydrogenatoms.
The oxygen atom and thehydrogen atom each donate oneelectron to the bond. The oxygenatom also has two pairs of nonbonding electrons, which can bedonated to form bonds with otherspecies.● In acidic solutions, each proton reactswith a water molecule to form ahydron iu m ion . A pair of non-bondingelectrons forms the new H-O bond:HNeutral water moleculeprotonspeciesHydroxide ion:deprotonated watermoleculeHydronium ion:protonated watermolecule2 Ammonia solution turns universal indicator blueHHHH+ + H2O ➞ H3O+● AnNHhydroxide ion is formed by the lossof a proton from a water molecule:OH2 OHH+ + OH-2 Ammonium ions● TheAmmonia molecule hasan extra protonHHNTo show the extraelectron in thehydroxide ionHHNH3 + H+ ➞ NH4 +● The four N-H bonds in the ammoniumion are directed toward the corners ofa tetrahedron, giving a similarstructure to methane.
This keeps thebonding pairs of electrons as far awayfrom each other as possible.OTo show the attraction between themolecules and the breaking of thebond in the molecule3 Schematic of protontransfer● Ammonia3 Schematic of proton transfer in diagram 2HHNHOHHNHHHmoleculesionsHOis very soluble in water anddissolves to form a weak alkalinesolution that is sometimes referred toas am m on iu m hydroxide:NH3 + H2O● AmmoniaNH4 OHNH4 + + OH-solution containsammonium ions, NH4 + , and hydroxideions, OH- , and has similar reactions tosolutions of soluble metal hydroxides,such as sodium hydroxide.© Diagram Visual Information Ltd.HHammonia molecule, NH3, has asimilar structure to the watermolecule, H2O, in the sense that thenitrogen atom has a pair of nonbonding electrons that it can donate toform a bond with another species.● Ammonia reacts with the protons in anacid to form the am m on iu m ion s:128CHEMICAL REACTIONSKey wordsacidbasehydronium ionlatticemagnesium oxideoxideprotonsaltProton transfer:neutralization of bases1 Magnesium oxide (MgO)solid and dilute acid2 The oxide ions attract thehydronium ionsNeutralizing bases● Metallicbases neutralize acids to forma salt plus water.1 MgO in acid● Magn esiu moxide consists of a regularlattice of magnesium ions, Mg2+ , andoxide ions, O2- .● An acid contains hydron iu m ion s,H3O+ .2 Attractions● Hydroniumions carry a positivecharge, while oxide ions carry anegative charge.
When solidmagnesium oxide is added to an acid,these oppositely charged ions areattracted to each other.watermoleculehydroniumionHHOOH + HH + HHHO +Hmagnesiumoxide latticeMg2+O2–Mg2+O2–O2–Mg2+H+ OHMg2+HO2–3 Transfer● Inan oxide ion, there are eightelectrons in the outer orbital of theoxygen atom.
Two pairs of electronsare donated to form bonds withoppositely charged hydronium ions:2H3O+ + O2- ➞ 3H2O3 Proton transfer takesplace4 A neutral solution isproduced and part of theoxide lattice has dissolved4 Neutral solution● Eachhydronium ion transfers a protonto the oxide ion, forming a moleculeof water.● The magnesium oxide lattice breaksdown, releasing magnesium ions intosolution.● The acid is neutralized, and a solutionof a magnesium salt is formed. Thenature of the salt depends on the acidused.HHOHHHO+ HOH +HOHHOHHMg2+© Diagram Visual Information Ltd.MgO(s) + 2HCl(aq) ➞MgCl 2(aq) + H2O(l)Hydrochloric acid ➞magnesium chlorideMgO(s) + 2HNO3(aq) ➞Mg(NO3) 2(aq) + H2O(l)Nitric acid ➞ magnesium nitrateMgO(s) + H2SO4 (aq) ➞MgSO4 (aq) + H2O(l)Sulfuric acid ➞ magnesium sulfateO2–Mg2+Mg2+O2–Mg2+O2–129Proton transfer:metallic carbonates1 Carbonate ions attracthydronium ionsCHEMICAL REACTIONSKey words2 Hydrogen carbonatemolecules and watermolecules are producedcarbonatecarbonic acidhydronium ionorbitalsaltMetallic carbonates● Metalliccarbon ates neutralize acids toform a metal salt, carbon dioxide, andwater.watermolecule1 Attraction● GroupOHHOprotontransferHO–HHHHOHOHO–HHOOCCcarbonate–ion (CO32 )O3 A hydrogen carbonatemolecule splitsO4 A carbon dioxide moleculeand water molecule areproducedHHOOOHCO● Theresult is the formation ofcarbon ic acid, H2CO3, and water:2H3O+ + CO32- ➞ H2CO3 + 2H2O3 H2CO3 splits● Carbonicacid is a weak acid that onlyexists in solution.
It readily breaksdown to carbon dioxide and water:H2CO3OC2 H2CO3 and waterHOH2O + CO24 CO2 and water● Inan acid–carbonate reaction, some ofthe carbon dioxide will remain insolution, but most will be given off asbubbles of gas.● The gas can be identified by bubblingit into limewater.
Carbon dioxide turnslimewater milky due to the formationof insoluble calcium carbonate.● The acid is neutralized by thecarbonate, and a salt is formed. Thenature of the salt depends on themetal carbonate and the acid used.© Diagram Visual Information Ltd.H1 metal carbonates are solublein water and can be used as solids orin solution. Other metal carbonatesare insoluble in water and are used assolids.● All metal carbonates contain thecarbonate ion, CO32- . All acids containthe hydron iu m ion , H3O+ .● Hydronium ions carry a positivecharge, while carbonate ions carry anegative charge. When a carbonate isadded to an acid, these oppositelycharged ions are attracted to eachother.● In a carbonate ion, each of the threeoxygen atoms has eight electrons in itsouter orbital.
A pair of electrons isdonated from two of the oxygen atomsto form bonds with oppositely chargedhydronium ions.130CHEMICAL REACTIONSKey wordsammoniacovalent bondhydrogenchlorideProton transfer:neutralization of acids1 Examples of moleculesNeutralizing acidsreact with acids to produce asalt and water.H● Bases1 Moleculesatom has seven electrons inits outer orbit. In hydrogen chloride,the chlorine atom forms a covalen tbon d with one hydrogen atom,forming the molecule HCl .● An oxygen atom has six electrons in itsouter orbit. In hydrogen oxide (water),the oxygen atom forms covalent bondswith two hydrogen atoms, forming themolecule H2O.● A nitrogen atom has five electrons inits outer orbit.
In am m on ia, thenitrogen atom forms covalent bondswith three hydrogen atoms, formingthe molecule NH3.lonepairsa hydrogen chloride molecule, eachchlorine atom is surrounded by eightelectrons: one pair of bondingelectrons and three pairs of nonbonding electrons (lone pairs).● In a water molecule, each oxygen atomis surrounded by eight electrons: twopairs of bonding electrons and twolone pairs of electrons.● In an ammonia molecule, eachnitrogen atom is surrounded by eightelectrons: three pairs of bondingelectrons and one pair lone pair ofelectrons.lone pairsHHlonepairsCl● A chlorine2 SchematicHOHlone pairslone pairsWater moleculeHydrogen chloridemoleculeHNlone pairsAmmonia molecule2 Schematic of the molecules shown in diagram 1HHHHHHClONHydrogen chloridemoleculeWater moleculeAmmonia molecule● In3 Proton transferClOHOHHH3 & 4 Proton transfer andschematicOClClH● Hydrogen© Diagram Visual Information Ltd.chloride gas is a covalentcompound and exists as diatomicmolecules.● When hydrogen chloride dissolves inwater, an acidic solution is formed:HHHA chlorine atom withone extra protonH2O + HCl ➞ H3O+ + Cl ● A lonepair of electrons from anoxygen atom is donated to create acovalent bond between the oxygenatom and a hydrogen atom, forming ahydronium ion and a chloride ion.● When hydrogen chloride is dissolvedin water, it forms an ionic compound.Attraction beginsHA water molecule withone extra protonTransfer of the protonis completeThe bond breaks4 Schematic of proton transferOHHHHHOClHCl131Collision theoryCHEMICAL REACTIONSKey words1 Collision theoryAactivation energyeffective collisionproductreactantABB1 Collision theoryNo collision between the particles of the reactants: no reaction● ReactionsABABWeak collision: no reactionABCDoccur when particles collidewith sufficient force to provide theenergy needed to start a reaction.● If particles collide with insufficientforce to start a reaction, they simplybounce off each other.● A collision that brings about a reactionis called an effective collision .
Particlesof reactan t collide, and particles ofprodu ct are formed:A+ Breactants➞C+ Dproducts● Notevery collision between particlesgives rise to a reaction, but every set ofparticles that do react have to collide.Effective collision: reaction2 Maxwell-Boltzmandistribution2 Maxwell-Boltzman distributionEAKinetic energy© Diagram Visual Information Ltd.all the particles of a particularchemical, element, or compound havethe same mass, the energy of theparticles is directly related to theirspeed.● In any mixture of moving particles, theenergy at which an individual particleis moving will vary.● The Maxwell-Boltzman distributionshows how the number of particles ina sample is distributed at differentenergies at a particular temperature.● There are no particles at zero energy.There are relatively few particles atvery high energy, but there is nomaximum energy value.● In order to react, particles need tohave a minimum amount of energy,called activation en ergy.
Theactivation energy is marked on thegraph by a line, parallel to the Y axis,at a point on the X axis thatsymbolizes the activation energy ( EA).Number of particles with energy (E)● Because132CHEMICAL REACTIONSKey wordsdiffusionimmisciblereactantsurface areaRates of reaction:surface area and mixing1 Total suface area2 cm1cmSurface areaorder for a reaction to take place,the reactan ts must come into contactwith each other. Thus, for a given massof reactant, the smaller the objects, thegreater the su rface area on which thechemical reaction can occur.
If all ofthe reactants are gases or liquids, it iseasy for them to mix, giving themaximum opportunity for the particlesto collide.2 cm1cm● In1cm2 cm2 Reduced surface area reaction1 Total surface area● Thereaction can only take place onthe surface of the solid.● A cube with sides 2 cm has a totalsurface area of 2 x 2 x 6 = 24 cm 2. Ifthe same cube is divided into 8 cubeswith sides 1 cm, the total surface areanow becomes 1 x 1 x 6 x 8 = 48 cm 2.granulatedzinczinc dust2 Reduced surface area● Zincreacts with dilute hydrochloricacid to form zinc chloride andhydrogen gas:3 MixingZn + 2HCl ➞ ZnCl 2 + H2● Thisreaction proceeds much morequickly if zinc dust (fine powder) isused rather than granulated zinc (largelumps).3 Mixingreactant particles are addedtogether, they will eventually mix bydiffu sion , and a reaction will takeplace.● Stirring reactants speeds the processof mixing so the reaction takes placemore quickly.© Diagram Visual Information Ltd.● WhenAAAAABBBAAstirringrapidBAABBABBABslowABBdiffusionBBABA4 Interface surface area4 Interface surface area● Ifone of the reactants is a liquid andone a gas, or if the two reactants areim m iscible liquids, then the reactioncan only take place at the interface.The larger the surface area of theinterface, the faster the reaction willtake place.smallinterfacelargeinterface133Rates of reaction:temperature andconcentrationCHEMICAL REACTIONSKey wordsactivation energyproductreactant1 Temperature (distribution of molecularenergies at T1 and T 2)1 Temperature● Temperatureis an important factor indetermining rate of reaction.● When temperature increases, theaverage speed of the particles in asubstance increases.
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