chemistry f4 chapter 8 salt


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chemistry f4 chapter 8 salt

  1. 1. STUDYSMART CHEMISTRY FORM 4 CHAPTER 8 : SALTS8.1 Synthesising Salts8.2 Synthesising qualitative analysis of salts8.3 Practising to be systematic and meticulous when carrying out activities8.1 SYNTHESISING SALTS A salt is a compound formed when the hydrogen ion, H+ from an acid is replaced by a metal ion or an ammonium ion, NH4+ Examples HCl + NaOH  NaCl + H2O 2HNO3 + Zn  Zn(NO3)2 + H2 H2SO4 + MgCO3  MgSO4 + H2O + CO2 Complete the table below Metal Sulphate salt Chloride salt Nitric Acid Carbonate salt Ion (From H2SO4) (From HCl) (From HNO3) (From H2CO3) Na+ K+ Zn2+ Mg2+ Ca2+ Fe2+ Fe3+ Cu2+ NH4+ Ba2+ Al3+ Pb2+ Ag2+ INSOLUBLE SALT 1 Study Smart
  2. 2. Solubility of salt. All K+ , Na+ and NH4+ salts are soluble All nitrate salts are soluble All carbonate are soluble except K2CO3, Na2CO3 and (NH4)2CO3 All Sulphate salts are soluble except BaSO4 , CaSO4, and PbSO4 All chloride salts are soluble except AgCl2 and PbCl2The preparation of salt on its solubility of the salt and the nature of the reaction. Preparation of salt METHOD 3 Soluble Insoluble METHOD 1 METHOD 2 K+ , Na+ NH4+ Other than K+ , Na+ - Mix two solution containing cations and NH4+ salts anions of insoluble salts - Stir using glass rod Acid + Alkali  Salt + H2O - Filter using filter funnel Acid + basic oxide  Salt + water - Rinse the residue with distilled water Acid + metal  Salt + Hydrogen gas - Dry the residue with filter paper Titration of acid and alkali Acid + Metal Carbonate  Salt + Water + CO2 - Add acid to the alkali until it is neutral with the aid of an indicator - Add basic oxide fillings/metals/metal carbonate to the acid and heat - Repeat the procedure without using an it until some of it no longer dissolves. (This mean all acid has reacted indicator with the basic oxide/metal/metal carbonate) - Filter to move excess solid residue 2 2 - Gently heat the filtrate to obtain a saturated solution (one-third of its original volume remains) - Cool the hot saturated solution to allow it to crystallize - Filter and dry the crystals by using filter paper Study Smart
  3. 3. TRY THIS 1Write all possible chemical equation to prepare soluble salts and chemical equation for insoluble salt *******KEY******* S = SOLUBLE SALT IS = INSOLUBLE SALT SALT SOLUBILITY CHEMICAL EQUATIONZinc Chloride Sodium NitrateSilver Chloride Copper(II) Sulphate Lead(II) Sulphate Aluminium Nitrate Lead(II) Chloride Magnesium Nitrate 3 Study Smart
  4. 4. Potassium Chloride Lead(II) Nitrate Barium Sulphate Ammonium SulphateNumerical problem involving stoichiometry reactions in the preparation of saltsA student prepare copper(II) nitrate, Cu(NO3)2 by reacting copper(II) oxide, CuO with 100 cm3 of 1.5mol dm-3 nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to reactcompletely with the acid. [RAM : Cu,64 ; O,16] 4 Study Smart
  5. 5. 8.2 SYNTHESISING QUALITATIVE ANALYSIS OF SALTS Colour of Salts SOLID AQUEOUS SOLID/METAL OXIDE White salt Colourless Green Insoluble Light Green Light Green Blue Blue Brown Brown Black Insoluble Yellow when hot Insoluble White when cold Brown when hot Insoluble Yellow when cold Confirmatory test for several gases GAS COLOUR SMELL EFFECT ON REAGENT CONFIRMATORY TEST DAMP USED LITMUS PAPERHydrogen Colourless Odourless No effect Lighted Bring a lighted splinter to the splinter mouth of test tube. It gives “pop” soundOxygen Colourless Odourless No effect Glowing Bring a glowing splinter to the Splinter mouth of test tube. The glowing splinter lights upCarbon Colourless Odourless Blue  red Lime water Bubble the gas produce intoDioxide lime water. Lime water will turns chalky/milky/cloudyAmmonia Colourless Pungent Red  blue Concentrated Dip a glass rod into Smell HCl concentrated HCl. White fumes is releasedChlorine Greenish Pungent Blue  red - - yellow Smell  whiteNitrogen Brown Pungent Blue  red - -Dioxide SmellSulphur Colourless Pungent Blue  red Acidified Turns acidified potassiumdioxide Smell potassium manganate (VII) solution from manganate(VII) purple to colourless solutionHydrogen Colourless Pungent Blue  red Concentrated Dip a glass rod intochloride Smell ammonia, NH3 Concentrated ammonia, NH3, aqueous white fumes is released 5 Study Smart
  6. 6. Action of heat on saltsa) Most compound which decomposes leave behind oxides Salt metal oxide + gas (residue identification (gas identification refers to specific cations refers to anion) only)b) Types of gas Colourless released residue Can predict the Can predict the identify of anions identify of cations presence in salt presence in saltc) Test of carbon dioxide gas liberated when the carbonate salt is heated strongly 6 Study Smart
  7. 7. d) Write down the chemical equation for the reactions that occur.Ion Carbonate Salt Nitrate Salt Is not decomposed by heat Decompose into O2 gas and metal nitrateK+Na+Ca2+ Decompose into metallic oxide and CO2 Decompose into metal oxide, NO2 and O2 2+MgAl3+Zn2+Fe2+Fe3+Pb2+Cu2+ Sulphate salts usually do not decompose Chloride salts do not decompose except NH4Cl NH4Cl (s) NH3 (g) + HCl (g) [sublimation]Confirmatory test for anions Unknown Salt Solution + H2SO4 dilute + dilute +HNO3 + HNO3 + FeSO4 acid + AgNO3 + Ba(NO3)2 + H2SO4 conc Gas turns __________ __________ ________ limewater Precipitate precipitate __________ formed formed ________ __Confirmatory test for cations a) The presence of cation can be detected by using two common bench alkalis namely i) _____________________________ solution ii) _____________________________ solution b) Write the ionic equation for the reaction of cations and sodium hydroxide The function of the alkalis is to produce a precipitate that is Metal hydroxide METAL + HYDROXIDE ION  METAL HYDROXIDE 7 Study Smart
  8. 8. Ion Ionic equation for the reaction of cations and sodium hydroxideAluminium ion Al3+ + 3OH-  Al(OH)3Lead (II) IonZinc IonMagnesium IonCalcium IonCopper (II) IonFerrum (II) IonFerrum (III) Ion 8 Study Smart
  9. 9. NH4+ Ca2+ , Fe2+ ,,Fe3+ , Zn2+ , Al3+, Pb2+ Cu2+ , Mg2+No Formation of Formation of white Fe2+ , Fe3+Precipitate precipitation & precipitate & then K2Fe(II)(CN)6 Light Blue Blue Non-soluble in soluble in excess precipitate precipitate excess K2Fe(III)(CN)6 Dark Blue Brown Precipitate Solution +NaOH a little KSCN No Change Red solution and then in excess + HCl, white precipitate CATIONS TEST occurs and dissolved in +NH4OH a little Fe2+ Fe3+ hot water and then in excessNH4+, Ca2+ Fe2+ ,,Fe3+, Al3+ Zn2+ Cu2+ Confirmatory test Pb2+ Pb2+, Mg2+ ,No Formation of precipitate isPrecipitate precipitation & formed & dissolve Not dissolve in in excess + KI, yellow precipitate excess NH4+ occurs and dissolved in ION TEST hot water Anion to be test: Examples CO32- SO42- Cl- NO3- + Nessler reagent, brown Anion Test Observation precipitate is form CO32- + HCl Gas form white precipitate with lime ANION TEST water Pre-Test SO42- + HCl White precipitate is + BaCl2/ Ba(NO3)2 formed Cl- + HNO3 White precipitate is + Ag(NO3)2 formed Confirmatory test Gas evolved from the NO3- + H2SO4 (Dil) Brown ring is formed reaction with salt + FeSO4 9 + H2SO4 (conc) Study Smart
  10. 10. Test for cationsCations Test with a small amount of NaOH solution Test with a small amount of NH4OH until in until in excess excessAl3+ White precipitate soluble in excess. NaOH White precipitate, insoluble in excess NH4OH solution solutionPb2+ White precipitate, soluble in excess NaOH White precipitate, insoluble in excess NH4OH solution solutionZn2+ White precipitate, soluble in excess NaOH White precipitate, soluble in excess NH4OH solution solutionMg2+ White precipitate, insoluble in excess NaOH White precipitate, insoluble in excess NH4OH solution solutionCa2+ White precipitate, insoluble in excess NaOH No precipitate solutionCu2+ Blue precipitate, insoluble in excess NaOH Blue precipitate, soluble in excess NH4OH solution solutionFe2+ Green precipitate, insoluble in excess NaOH Green precipitate, insoluble in excess NH4OH solution solutionFe3+ Brown precipitate, insoluble in excess Brown precipitate, insoluble in excess NH4OH NaOH solution solutionNH4+ No precipitate No precipitate 10 Study Smart