Chemistry - an illustrated guide to science (794128), страница 11
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However thesolubility of some is so low that theyare best regarded as in solu ble.Solubility generally follows thefollowing rules.● All ammonium, potassium, andsodium salts are soluble.● All nitrates are soluble.● With the exception of lead and sliverbromides, chlorides, and iodides,bromides, chlorides, and iodides aresoluble.● Most sulfates are soluble, with theexception of barium and lead sulfate.● Most carbonates are insoluble, withthe exception of ammonium,potassium, and sodium carbonate.● Most hydroxides are insoluble, withthe exception of ammonium,potassium, and sodium hydroxides.● Calcium hydroxide is only slightlysoluble.Formula of compoundPercentage of solidsin seawatersodium chlorideNaCl78magnesium chlorideMgCl 29magnesium sulphateMgSO47calcium sulphateCaSO442 Most abundantcompounds in seawaterpotassium chlorideKCl2● Seawatercalcium carbonateCaCO3less than 1magnesium bromideMgBr 2less than 1magnesiumbromide<1 %sodiumchloride78 %magnesiumchloride9%magnesiumsulfate7%calciumsulfate4%potassiumchloride2%calciumcarbonate<1 %is a solution of manydifferent salts.
The main salt present inseawater is sodium chloride.● The concentration of solids inseawater depends on the location. Thesaltiest water occurs in the Red Sea,where there is 40 g of dissolved solidsper 1,000 g of water. The NorthAtlantic is the saltiest of the majoroceans, with an average of 37.9 g ofdissolved solids per 1,000 g of water.The least salty waters are found inpolar seas and the Baltic Sea, whichcontains only 5–15 g of dissolvedsolids per 1,000g of water.© Diagram Visual Information Ltd.most bromides, chlorides, and iodides62CHANGES IN MATTERSolubility curvesKey words120solubility curvea110a potassium nitrateb sodium chloridec potassium sulfateExpressing solubility● Solubility10 09080Mass of crystals that dissolve in 10 0 g of water (g)is normally expressed ing / 100 g of water. The solubility of acompound varies (normally increases)with temperature, so when quotingsolubility, it is necessary to state thetemperature for which it is given.● A solu bility cu rve is a graph thatshows how the solubility of a saltvaries between 0°C (the freezing pointof water) and 100°C (the boiling pointof water).● The solubility curve of a compound isplotted using data about the solubilityof the compound over the wholetemperature range.
Solubility curvesare generally not straight lines.● Over the temperature range 0–100°C,the solubility of some salts remainsnearly constant (sodium chloride),while the solubility of others eitherincreases gradually (potassium sulfate)or increases very rapidly (potassiumnitrate).70605040b30c© Diagram Visual Information Ltd.201000102030405060Temperature (°C)70809010 063Solubility of copper(II)sulfateCHANGES IN MATTERKey wordssaturatedsolutesolutionsolubility curve1 Table of solubility of copper(II) sulfate atdifferent temperaturesTemperature °CSolubilityg/ 10 0 g waterTemperature °CSolubilityg/ 10 0 g water014.36040.01017.47047.12020.78055.03024.39064.84028.510 075.45034.01 Solubility of copper(II)sulfate at differenttemperatures● Whenno more solid will dissolve in asolu tion at a given temperature, thesolution is said to be satu rated.● Normally when a solution is cooledbelow the saturation temperature forthe quantity of solu te present, somesolute crystallizes out.
Under certainconditions a solution may be cooledbelow this temperature withoutcrystallization occurring. Such asolution is said to be supersaturated.● A solu bility cu rve is plotted by findingthe amount of solid needed to make asaturated solution at a number ofdifferent temperatures over the range0–100°C.2 Solubility curve for copper(II) sulfate70+602 Solubility curve forcopper(II) sulfate+Solubility g/ 10 0 g water50++40+30++20++1000102030405060Temperature (°C)70809010 0solubility of copper(II) sulfate at76°C is found by drawing a vertical linefrom 76°C to the solubility curve andthen a horizontal line to the solubilityaxis.
The value is 52 g of copper(II)sulfate per 100 g of water.● The temperature at which thesolubility of copper(II) sulfate isexactly 36 g per 100 g of water isfound by drawing a horizontal linefrom 36 g / 100 g water to thesolubility curve and then a vertical lineto the temperature axis. Thetemperature is 54°C.● The solubility of copper(II) sulfate at90°C is 64.8 g / 100 g water and at 20°Cis 20.7 g / 100 g water. If 100 g ofsaturated copper(II) sulfate solutionwas allowed to cool from 90°C to 20°Cthe mass of copper(II) sulfate crystalsformed would be 64.8 – 20.7 = 44.1 g.● The size of crystals formed is relatedto how quickly the solution is cooled.If cooling is rapid many small crystalsare formed but if cooling is slow asmaller number of large crystals areformed.© Diagram Visual Information Ltd.● The64PATTERNS—NON-METALSKey wordsanhydrousdry gashydrochloric acidhydrogenHydrogen: preparation1 Obtaining hydrogen using Kipps apparatus1 Obtaining hydrogen usingKipps apparatus● Traditionally,hydrogen is generatedusing a Kipps apparatus.
When the tapis opened, dilute hydrochloric acidfloods the bottom compartment andthe level rises until it reacts withgranulated zinc in the middlecompartment. Zinc reacts with dilutehydrochloric acid to producehydrogen:cZn(s) + 2HCl(aq) ➞ ZnCl 2(aq) + H2(g)● Ifthe tap is closed, hydrogencontinues to be produced for a shorttime, and the pressure of the gas inthe middle compartment graduallyincreases. Eventually the pressure issufficient to force the dilutehydrochloric acid back down and outof the middle compartment, and thereaction stops.● In a modern laboratory, hydrogen isoften obtained directly from a cylinderof the gas.2 Collecting dry hydrogenba granulated zincb dilute hydrochloric acidc hydrogen gas2 Collecting dry hydrogen● A dry© Diagram Visual Information Ltd.gas is a natural gas from whichall water vapor has been reduced.● Hydrogen is dried by passing throughan hydrou s calcium chloride.
The gasis collected by upward delivery(downward displacement of air)because it is less dense than air.aabca damp hydrogen fromKipps apparatusb anhydrous calciumchloridec gas65Hydrogen: comparativedensityPATTERNS—NON-METALSKey wordscarbon dioxidediffusionGraham’s lawhydrogen1 Gaseous diffusion of hydrogen in air1B1Aaabbccdd1 Gaseous diffusion ofhydrogen● Gasesare able to pass into and out ofa porous vessel.● Hydrogen is less dense than air, so it iscontained in an inverted beaker (1A).● Hydrogen diffuses into the porousvessel more quickly than air diffusesout of it.● The gas pressure inside the porousvessel increases and becomes greaterthan atmospheric pressure (1B).Liquid is forced up the right side ofthe manometer (an instrument usedto measure the pressure of a fluid).2 Gaseous diffusion ofcarbon dioxide● Carbondioxide is more dense thanair, so it is contained in an uprightbeaker (2A).● Carbon dioxide diffuses into theporous vessel more slowly than airdiffuses out of it.● The gas pressure inside the porousvessel decreases and becomes lessthan atmospheric pressure.
Liquid isforced up the left side of themanometer (2B).2 Gaseous diffusion of carbon dioxide in air2B2AComparative densitybcceeda hydrogenb airdc porous vesseld manometere carbon dioxidelaw of diffu sion states thatthe rate at which a gas diffuses ( r ) isproportional to the square root of 1over its density ( d ):r ! "1/ d● The density of hydrogen is lower thatair. Therefore, it diffuses more quickly.● The density of carbon dioxide ishigher that air. Therefore it diffusesmore slowly.© Diagram Visual Information Ltd.● Graham ’sb66PATTERNS—NON-METALSKey wordsanhydrousanodecalciumcarbonatecathodeelectrolysishydrogen sulfidelead sulfidephotochemicalreactionsulfuric acidHydrogen: reaction withother gases1 Explosion of hydrogen/ oxygen mixtureba1 Hydrogen and oxygen● Electrolysisof dilute su lfu ric acidproduces oxygen at the an ode(positive electrode) and hydrogen atthe cathode (negative electrode).● At the anode:b4OH- (aq) ➞ O2(g) + 2H2O(l) + 4e-c● AtdfeExplosion techniquethe cathode:4H+ (aq) + 4e- ➞ 2H2(g)Preparation of hydrogen and oxygen from electrolysisof sulfuric acid● A mixtureof hydrogen and oxygenexplodes when ignited:2H2(g) + O2(g) ➞ 2H2O(g)2 Hydrogen and air2 Hydrogen and air● Hydrogenburns in air to producewater.● The hydrogen gas is dried by passing itthrough an hydrou s calciu mcarbon ate so any water producedmust be the result of combustion.● Water vapor condenses on the outersurface of the beaker of cold water andcollects in the water glass.● The liquid turns anhydrous blue cobaltchloride paper pink, showing it iswater.3 Reaction of hydrogenwith sulfurgiljnmkh3 Hydrogen and sulfur4 Photocatalytic explosion of hydrogen with chlorine● Hydrogenreacts with sulfur toproduce hydrogen su lfide:H2(g) + S(l) ➞ H2Sqsulfide turns damp leadacetate paper black due to theformation of lead su lfide:r● HydrogenpoPb 2+ (aq) + H2S(g) ➞ PbS(s) + 2H+ (aq)4 hydrogen and chlorine© Diagram Visual Information Ltd.● A mixtureof hydrogen and chlorinereact in bright light.● This is an example of a photochem icalreaction .
Light provides the energyneeded for the reaction to start:H2(g) + Cl 2(g) ➞ 2HCl(g)Before light is switched onabcdefghijpolyethylene bottle containing dilute H2SO4platinum electrodespolyethelene tubingbunsen flameloose supporthydrogen/ oxygen mixturehydrogen from Kipps apparatusanhydrous calcium chloridebeaker containg cold waterhydrogen burningLight is switched onk water collectedl dry hydrogenm boiling sulfurn filter paper soaked in lead acetateo polyethylene bottle containing mixture ofchlorine and hydrogenp powerful light sourceq rubber bungr white fumes of hydrogen chloride67Hydrogen: anomalies inammonia and water1 Anomalous boiling points of ammonia and waterPATTERNS—NON-METALSKey wordsammoniaboiling pointdipolegroup 5group 6group 8hydridelone pairorbitalH2 O1001 Anomalous boiling pointsof ammonia and water● AtomsH2Tegroup 6 hydrides0Boiling point/ °CNH3group 5 hydridesH2SeSbH3H2 S–50AsH31group 8 hydridesPH3–100Xe2–150Kr–2001 expected value for waterAr2expected value for ammonia–250Ne–30012435Period number2 Strong bonding between water moleculesNδ+ HHHδ–NNHHδ–HHδ+HH6of the grou p 8 elements have afull outer orbital of electrons.
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