Question

LILIISSIUI Map Trace amounts of rare elements are found within groundwater and are of interest to geochemists. Europium and terbium are lanthanide-series elements that can be measured from the intensity of their fluorescence emitted when a solution is illuminated with ultraviolet radiation. Certain organic compounds that bind Eu(III) and Tb(lll enhance the emission, and substances found in natural waters can decrease the emission. For that reason it is necessary to use standard additions to the sample to correct for such interference. The graph at the right shows the result of such an experiment in which the concentration of Eu(lll) and Tb(III) was measured in a sample of groundwater. Eu(lll) - 23.0 mL In each case 10.00 mL of sample solution and 15.00 mL of of organic additive were placed in 50-ml volumetric flasks. Eu(III) standards (0, 5.00, 10.00, 15.00, and 20.00 mL) were added and the flasks were diluted to 50.0 mL with water. Tb(111) -9.91 ml -25 -20 -15 -10 -5 0 5 10 15 20 25 Added volume of Standard (mL) (a) Eu(III) analysis The Eu(lll) standards added to the groundwater sample contained 0.147 ng/mL (ppb) of Eu(ill). Calculate the concentration of Eu(lll) in the groundwater sample. (b) Tb(III) analysis The Tb(lll) standards added to the groundwater sample contained 14.7 ng/mL (ppb) of Tb(ill). Calculate the concentration of Tb(ill) in the groundwater sample. Number Number ng/ mL ng/mL

Answer 1

a, Eu(III) analysis : Standard added volime, Vs = - 23 mL Volume, Vo = 10ML concentration of Standard, [s]} = 0.147.ng/mi We know that, Dodi --Esli chod) | DJ = 0 338 ng! ) b, Tolim analysis Standard added volume, Vs = -9.91ML- Inutial volumo, VOETOML [S]; = 14,7ng).ml {xi =- [s]; ( vera 3+14+ ng lmi (-9 mL) {Xi = 14.56ng/mL)