Pure Chem Notes 2023

CHEMPRACTICAL01-Acid An acid is a substance which produces ions in aqueous Solution. Strong𝐻 + Acids completelyioniseinwater togivehighconcentrationof ionsinaqueous𝐻 + solution. Weak acids partially ioniseinwater togivelowconcentrationof ions𝐻 + inaqueoussolution CommonAcids Name Formula Strength HydrochloricAcid 𝐻𝐶𝑙 Strong SulfuricAcid 𝐻₂𝑆𝑂₄ Strong NitricAcid 𝐻𝑁𝑂₃ Strong EthanoicAcid 𝐶𝐻₃𝐶𝑂𝑂𝐻 Weak Properties- Sour Taste- pHlessthan7- Turnsbluelitmuspaper redChemical Reactions- Acid+base→salt +water (neutralisation)- Acid+metal →salt +H ₂ gas- Acid+carbonate→salt +water +CO ₂ gasTest For Gases Gas Test Result Hydrogen Lightedsplint Extinguishwith‘pop’sound CarbonDioxide Limewater Whiteppt

BaseAbaseisasubstancewhichreactswithacidtoproducesalt andwater only.● Basesincludemetal oxides, metal hydroxidesandaqueousammonia● Basescanbesolubleor insolubleinwater● AlkalisaresolublebasesAlkaliAn alkali is a substance which produces ions in aqueous solution. Strong𝑂𝐻⁻ٰalkalis completely ionise in water to give high concentrations of inanaqueous𝑂𝐻⁻ٰsolution. Weak alkalis partially ionise to give low concentrations of in aqueous𝑂𝐻⁻ٰsolutions.CommonAlkalis Name Formula Strength Sodiumhydroxide 𝑁𝑎𝑂𝐻 Strong Potassiumhydroxide 𝐾𝑂𝐻 Strong Calciumhydroxide 𝐶𝑎(𝑂𝐻)₂ Weak Aqueousammonia 𝑁𝐻₃ Weak Properties- Bitter taste- pHmorethan7- Turnsredlitmuspaper blueChemical reactions- Base/ Alkali +acid→salt +water (neutralisation)- Alkali +ammoniumsalt →salt +water + gas𝑁𝐻₃ Test for gas Gas Test Result Ammonia Dampredlitmuspaper Turnsblue

SaltSolubility Salt Preparation Solubilityof Salt Method Separationtechnique Soluble Titration Crystallisation Acid+excessinsolublesolid(base, metal,carbonate) Filtration, thencrystallisation Insoluble Precipitation Filtration SamplePlanningQns:1. Plananexperiment topreparecleandrycrystalsof sodiumchloride2. Describe a suitable method to prepare a clean dry sample of bariumsulfate3. Outline the steps to determine the water of crystallisation in a sample ofhydratedcopper (II) sulfate

SAMPLE:Xcanbeusedtomakelead(II)sulfate.StartingfromX, describeamethodthat canbeusedtomakeapure, drysampleoflead(II)sulfate.Youaregivenasolutionof lead(II) nitrate. Youcanassumethat all theapparatusandreagentsnormallyfoundinaschool laboratoryareavailable. [5] Precipitationoflead(II)nitrate1. Addanexcessofaqueoussilver nitratetoX.Thought Process: Excess silver nitrate needed to precipitate as much chloride as possible. Silver chloridewill be formed. Silver chloride is insoluble. Aqueous bariumnitrate should not beusedasinsolublebariumsulfatewill beformed. 2. Filter themixture.Thought Process: Residueissilver chloride, filtratecontainssilver ions, sulfateionsandnitrateions. 3. Keepthefiltrate.4. Addanexcessofaqueouslead(II)nitratetothefiltrate.Thought Process Insoluble lead (II) sulfate will beformed. Theremainingsolutioncontainssilver ions, lead(II)ionsandnitrateions. 5. Filter themixture.6. Keeptheresidue.Thought Process Residue is lead (II) sulfate, filtrate contains lead (II) ions, silver ions and nitrate ions. Purificationoflead(II)nitrate1. Rinsetheresiduewithasmall volumeofcolddistilledwater.2. Drytheresiduebetweenpiecesofcleandryfilter papers.

02-QualitativeAnalysisTest forcations● Alkalisareusedtotest for cations● Afewdropsofalkali areadded, theninexcess● Hydroxidesareformed● Thehydroxidesformedmaybesolubleor insolubleinexcessalkali● If thehydroxidereactsanddissolvesinexcessalkali, thecolour ofthefinalsolution must be described. If the hydroxide is insoluble, it forms aprecipitate(ppt)● Lead(II)iosnot testedinpractical but maybetestedinplanning Cation AqSodiumHydroxide AqAmmonia Eqn Aluminium( )𝐴𝑙³⁺ Whiteppt,solubleinexcessgivingcolourlesssolⁿ Whiteppt,insolubleinexcess 𝐴𝑙³⁺+ 3𝑂𝐻 →𝐴𝑙(𝑂𝐻)₃ Ammonium( )𝑁𝐻₄⁺ Ammoniaproducedonwarming - - Calcium( )𝐶𝑎²⁺ Whiteppt,insolubleinexcess Noppt 𝐶𝑎²⁺+ 𝑂𝐻 → 𝐶𝑎(𝑂𝐻)₂ Copper(II)( )𝐶𝑢²⁺ Lightblueppt,insolubleinexcess Lightblueppt,solubleinexcessgivingdarkbluesolⁿ 𝐶𝑢²⁺+ 𝑂𝐻 → 𝐶𝑢(𝑂𝐻)₂ Iron(II)( )𝐹𝑒²⁺ Red-Brownppt,insolubleinexcess Greenppt,insolubleinexcess 𝐹𝑒²⁺ + 𝑂𝐻 → 𝐹𝑒(𝑂𝐻)₂ Iron(III)( )𝐹𝑒³⁺ Red-brownppt,insolubleinexcess Red-Brownppt,insolubleinexcess 𝐹𝑒³⁺ + 𝑂𝐻 → 𝐹𝑒(𝑂𝐻)₃ Lead(II)( )𝑃𝑏²⁺ Whiteppt,insolubleinexcessgivingcolourlesssolⁿ Whiteppt,insolubleinexcess 𝑃𝑏²⁺ + 𝑂𝐻 → 𝑃𝑏(𝑂𝐻)₂ Zinc( )𝑍𝑛²⁺ Whiteppt,insolubleinexcessgivingcolourlesssolⁿ Whiteppt,insolubleinexcessgivingcolourlesssolⁿ 𝑍𝑛²⁺ + 𝑂𝐻 → 𝑍𝑛(𝑂𝐻)₂

03-Redox Reduction Oxidation Gainofelectrons Lossofelectrons Gainofhydrogen Lossofhydrogen Lossofoxygen Gainofoxygen Decreaseinoxidationstate IncreaseinOxidationstate RedoxAgent Itself OtherSubstance Example OxidisingAgent Reduced Oxidised Potassiummanganate(VII)( )𝐾𝑀𝑛𝑂₄Potassiummanganate(VI) ReducingAgent Oxidised Reduced PotassiumIodide( )𝐾𝐼 CommonRedoxReagents Test For RedoxReagent Typeofagent Start Colour ColourChange ReducingAgent 𝐾𝑀𝑛𝑂₄ OxidisingAgent Purple Colourless ReducingAgent 𝐾₂𝐶𝑟₂𝑂₇PotassiumDichromate(VI) OxidisingAgent Orange Green OxidisingAgent 𝐾𝐼 ReducingAgent Colourless Brown

Test ForAnions● Eachanionistestedusingdifferent reagents● Insolubleppt formedareinsolublesalts● Colour ofppt formedmust bedescribed● Acid is added in some tests to remove insoluble carbonates which formppt Anion Test Result Ppt Eqn Carbonate( )𝐶𝑂₃²⁻ AddDiluteNitricAcid Effervescence𝐶𝑂₂ 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 - 𝑎𝑐𝑖𝑑 + 𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒 →𝑠𝑎𝑙𝑡 + 𝐻₂𝑂 + 𝐶𝑂₂ Chloride( )𝐶𝑙⁻ Acidifywithdilutenitricacid, addaqsilver nitrate Whiteppt Silver Chloride( )𝐴𝑔𝐶𝑙 𝐴𝑔⁺ + 𝐶𝑙⁻→𝐴𝑔𝐶𝑙 Iodide( )𝐼⁻ Acidifywithdilutenitricacid, addaqsilver nitrate Yellowppt Silver Iodide( )𝐴𝑔𝐼 𝐴𝑔⁺ + 𝐼⁻→𝐴𝑔𝐼 Nitrate( ₃⁻ )𝑁𝑂 Addaqsodiumhydroxide, addaluminiumfoil.Warmcarefully 𝑁𝐻₃ 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 - - Sulfate( )𝑆𝑂₄²⁻ Acidifywithdilutenitricacid, addawbariumnitrate Whiteppt BariumSulfate( )𝐵𝑎𝑆𝑂₄ 𝐵𝑎²⁺ + 𝑆𝑂₄²⁻→𝐵𝑎𝑆𝑂₄ Acidifywithdilute, addaq𝐻𝐶𝑙bariumchloride

Test forGases● Eachgasistestedusingdifferent reagents● Sulfur Dioxidewill not betestedastoodangerous Gas Test Result Ammonia( )𝑁𝐻₄ Dampredlitmuspaper TurnsBlue CarbonDioxide( )𝐶𝑂₂ Limewater TurnsRed Chlorine( )𝐶𝑙₂ DampLitmuspaper Bleaches Hydrogen( )𝐻₂ LightedSplint Extinguishedwith‘pop’ sound Oxygen( )𝑂₂ GlowingSplint Relights Sulfur Dioxide( )𝑆𝑂₂ Aqacidified𝐾𝑀𝑛𝑂₄ Turnsfrompurpletocolourless Aqacidified𝐾₂𝐶𝑟₂𝑂₇ Turnsfromorangetogreen ExperimentsonqualitativeanalysisQualitative analysis experiments may involve identification of unknown ioniccompound(s). Morethan1chemical test will berequired.Practical tips● Tests for ions and gases are given in the ‘Notes for Qualitative Analysis'providedat thebackofthepractical exampaper.● It isadvisabletomemoriseasmanyofthetestsaspossible.● Recordall observationsandconclusions, includingnegativeresults.● For negativeresults, writenovisiblechange/reactionor nogasproduced.● For any unknown chemical tests, performthe chemical test followingtheinstructionsgivenandrecordyour observations(for example, colour ofpptor solution, effervescence, smell of gas). You do not need to writeconclusions.Testsforgases● When effervescence is observed, cover the test tube opening with yourthumbtoprevent gasfromescaping.● Test for themost likely gasbasedonyour knowledgeof thecompound. Ifyouarenot surewhat gasisproduced, tryall testsfor gases.

SafetyNotes- Ammonia,chlorineandsulfurdioxidearetoxicgases.- Pointtheopeningofthetesttubeaway fromyourselfandothersto reduceexposure to toxicgases.- Donotsmelldirectlyattheopeningofthetesttube.Donotplacetheopeningofthetesttubedirectlybelowyournose.- Placetheopeningofthetesttubenearyournose.- Useonehandtogentlyfanthegasfromtheopeningofthetesttubetowardsyournose. Test forammoniaandchlorine1. Put one drop of distilled water on one piece of litmus paper to moisten itbeforeuse.2. Youshouldsmell thepungent smell ofammoniaor chlorinegas.3. Insert thedamplitmuspaper intothetest tubeor placeit near theopeningofthetest tube4. Makesurethat thedamplitmuspaper doesnot touchtheopeningor sidesofthetest tube5. Ifammoniagasispresent, thedampredlitmuspaper will turnblue.6. Ifchlorinegasispresent, thedampredor bluelitmuspaper will tur