Part lIC Scoring Scheme: 3-3-2-1 Using the equivalent millimoles HCl/mg sample,

Question

Part lIC Scoring Scheme: 3-3-2-1 Using the equivalent millimoles HCl/mg sample, the stoichiometry of reaction of HCI with NaOH, and the molar mass of the hydroxide ion, report the gram equivalent OH per gram of antacid for each of your three trials Report them in the same sequence as all your trial data has been reported and use 4 significant figures Vol Vol mmoles mmoles mass tablet(g) antacid(g) HCl(mL)NaOH(mL) HC/mgHCL/tablet antacid 1.304 1.304 1.304 mass Entry # #2: #3: 0.6200 0.6100 0.6120 14.00 14.00 14.00 10.20 9.200 7.800 0.007834 0.008131 0.008340 10.21 10.60 10.87

Explanation / Answer

The method of back -titration is used to analyse the gram OH- equivalent of NaOH(or, the equivalent of base per gram of the tablet),

The antacid tablet is dissolved in excess HCl(known concentration),which it neutralizes partly,and then the remaining excess HCl is titrated against NaOH of known concentration.So ,actual concentration of HCl neutralized by antacid can be calculated using the equation:

Conc(Antacid)=Conc of HCl used-conc of HCl neutralized by NaOH

As the calclations for mmoles HCl/tablet(g) is already done, so we can equate it to get the result as follows:

trial 1)

g HCl/g tablet=mmol HCl*(10^-3 mol/mmol)*(molar mass of HCl)

=(0.007834 mmol HCl)*(10^-3 mol/mmol)*(36.46g/mol)

=0.0002856gHCl/g tablet

trial 2

g HCl/g tablet=mmol HCl*(10^-3 mol/mmol)*(molar mass of HCl)

=(0.008131 mmol HCl)*(10^-3 mol/mmol)*(36.46g/mol)

=0.0002964gHCl/g tablet

trial 3)

g HCl/g tablet=mmol HCl*(10^-3 mol/mmol)*(molar mass of HCl)

=(0.008340 mmol HCl)*(10^-3 mol/mmol)*(36.46g/mol)

=0.0003041 gHCl/g tablet

HCl +NaOH --->NaCl+H2O

1 mol HCl (36.46g/mol) reacts with 1 mol NaOH (39.997 g/mol)

36.46 g HCl is equivalent to 39.997 g NaOH

Conversion factor for g HCl to g NaOH: 39.997g OH-/36.46 g HCl

trial 1)

0.0002856gHCl/g tablet = 0.0002856gHCl *(39.997g OH-/36.46 g HCl)=0.000313 g OH- /g antacid tablet

trial 2)

0.0002964gHCl/g tablet = 0.0002964gHCl/g tablet *(39.997g OH-/36.46 g HCl)=0.000325 g OH-/antacid tablet

trial 3)

0.0003041 gHCl/g tablet=0.0003041 gHCl/g tablet *(39.997g OH-/36.46 g HCl)=0.000334 g OH-/antacid tablet

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