G sulfuric acid and the solution level is altered to

This preview shows page 10 - 13 out of 31 pages.

A burette is filled with a solution of known concentration (e.g. sulfuric acid)and the solution level is altered to the zero mark2.A solution of the sample to be analysed (e.g. sodium hydroxide) is placed in aflask under the burette3.Indicator is added to the flask4.Solution is slowly run from the burette into the flask with continuous swirlinguntil the indicator just changes colour (called the end point)Note: The equivalence point is when the reaction is complete (e.g. thesolution is neutral); the end point determines the equivalence point5.The volume in the burette is read6.The required concentration is thus calculated using this methode.g. the volume of NaOH is 25 mLThe found volume of H2SO4is 17.5 mL and the [H2SO4] is 0.1 mol.L-1H2SO4 (aq)+ 2NaOH (aq)→ Na2SO4 (aq)+ 2H2O (aq)nH2SO4=cV=(0.1) (0.0175)=1.75×103molnH2SO4=2nNaOHnNaOH=8.75×104molc=nV=8.75×104.025=.035mol .L1Back Titrations10
oSometimes there are practical reasons for wanting to analyse a substance byadding a known excess of a reagent (reactant) to it and then titrating theexcessoFor example, suppose we wanted to determine the amount of CaCO3in asample of limestoneoSince suspending the insoluble limestone in water and titrating would beinefficient and inaccurate, it is simpler to add a known excess of HCl to thelimestoneoThe excess HCl may then be titrated with a standard solution of NaOH.oThis is called a back titration, and the calculation works as follows:e.g. 1.066 g of limestone is placed in water and 50 mL of .411 mol.L-1HCl is added. The mixture was back titrated with .208 mol.L-1NaOHwhere 16.4 mL was required. Calculate the mass of CaCO3in thelimestoneHCl + NaOH → NaCl + H2Oc1v1= c2v20.208 × 0.0164 = 0.411 × vHCl8.3 mL of HCl reacted with NaOH41.7 mL of HCl reacted with CaCO30.017 mol of HCl reacted with CaCO32HCl + CaCO3→ CaCl2+ CO2+ H2OCaCO3: HCl → 1:20.009 mol of CaCO3was in the limestonem=nM=(0.009) (40.08+12.01+3×16)=0.858g0.858 g of CaCO3was in the limestoneAlkanolsoAlkanols are the OH functional groupoIts general formula is ROH, where R is a C-chain.CnH2n+1OH is the formula for ‘n’ carbon atomsoIts suffix is –anol (e.g. if the C-chain is one long, it is methanol)oIt is polar, and has H-bonding.oA primary alkanol is an alkanol where the C atom attached to the OH grouphas no more than one C atom attached to it.oA secondary or tertiary alkanol is the same as above, but with 2 and 3 Catoms respectively.Alkanoic AcidsoAlkanoic acids are the COOHfunctional group.oIts general formula is ROH, where R isa C-chain.Cn-1H2n+1COOH is the formulafor ‘n’ carbon atomsoIts suffix is –anoic acid.oAlkanoic acids have greater m.p. and b.p. than alkanols as they have greaterintermolecular bondsEsters11
oAn ester is an organic compound derived from an alkanol and an alkanoic acidcontaining the COO functional group.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture