0 SIMPLE REACTIONS Soving a redox titration problem - O Jacob To measure the amo

Question

0 SIMPLE REACTIONS Soving a redox titration problem - O Jacob To measure the amount of calcium carbonate (CaCO3) in a seashell, an analytical chemist crushes a 3.800 g sample of the shell to a fine powder and titrates it to the endpoint with 257. mL of 0.2100 M hydrogen chloride (HCI) solution. The balanced chemical equation for the reaction is: 2HClag) coj(aa) - H,CO,(ag) +2CI (aq) alo precipitation | Og DioP x10 What kind of reaction is this? acid-base Ar redox ?? If you said this was a precipitation reaction, enter the chemical formula of the precipitate If you said this was an acid-base reaction, enter the chemical formula of the reactant that is acting as the base If you said this was a redox reaction, enter the chemical symbol of the element that is oxidized. Calculate the mass percent of CaCO3 in the sample. Be sure your answer has the correct number of significant digits

Explanation / Answer

i) Acid base reaction

ii) CaCO3 acting as base

iii) 2HCl(aq) + CO32-(aq) - - - - - - > H2CO3(aq) + 2Cl-(aq)

stoichiometrically, 2moles of reacting with 1mole of CaCO3

no of moles of HCl consumed = (0.2100mol/1000ml)×257ml = 0.05397

Therefore,

No of moles of CaCO3 present in solution = 0.05397mol/2 = 0.026985

molar mass of CaCO3 = 100.09g/mol

mass of CaCO3 present in solution = 100.09g/mol × 0.026985mol = 2.7009g

mass % CaCO3 =( 2.7009g/3.800g)×100 = 71.08%

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