Question

You are using gravimetric analysis to determine the concentration of calcium (Ca2+) in tap water. The calcium is precipitated as calcium oxalate monohydrate upon addition of ammonium oxalate to the tap water according to the following reaction:

Ca +2 (aq) + C2O4 -2 (aq)   → CaC2O4 ∙H_2 O (s)    Ksp = 1.3 x 10 -8

The protocol calls for addition of 25 mL of 1.0 M ammonium oxalate to 25 mL sample. In order to ascertain the accuracy of your method, you fortify a second tap water sample (25.0 mL) with calcium (2.00 mL of 0.100 M Ca2+) and precipitate the calcium as with the original sample. Once the precipitate is collected and dried you determine the following masses of calcium oxalate monohydrate:

Sample - 0.0326 g precipitate
Fortified sample – 0.0597 g precipitate

Calculate the % recovery of the added calcium

Answer 1

Given 2- CaC2Oy + H20 Cot Caou Calcium To Calculare,eecoeky gadded Moleculas keight Calcium 40-078 ammonium xalate menehetase Calcium ouatate monahu arate 124.1 9lmol 46.11 We have .0 M ammonium oxalate 25 ml Sample 2s m) a Sample + 2.0 ml o .1 M Ca2 pvecipitate ohnined Sample Fortified Sample= 2+ 0.03269

Date lets Calaulare Solution Ca2t io 2.0 ml m o-1M mass 46.48 in 1000 m in .1 M 2.0 m) 40.48 x2 XO.1 008 ofCalcium Fortified Sample has Carcium onalate. Qut o Lohich O'O326 sample onaloste om top watex 0A097-0.0326 0271 oCalciuo axalate caicium ebtained from 0271 added Ca Ca 146.11 aO COC2O4 H20 .0241 gavea giea 40.078 40 078 XO 0231 196.11 00743 % Recovery .00743 X LO0 O008 92.9 %