Question

In one experiment, Marie Curie dissolved 0.09284 g of RaCl2 and treated it with excess AgNO3 to precipitate 0.08979 g of AgCl. In her time (1900), the atomic mass of Ag was known to be 107.8 and that of Cl was 35.4. From these values, find the atomic mass of Ra that Marie Curie would have calculated.

Answer 1

RaCl2 + 2 AgNO3 ----------------------------->       2 AgCl    + Ra(NO3)2

x g                                                                   286.4 g

0.09284 g                                                           0.08979 g

RaCl2 mass initial x =    286.4 x 0.09284 / 0.08979

                                 = 296.1 g

RaCl2 molar mass = 296.1 g

Ra + 71 =296.1

Ra = 225.3 g /mol

atomic mass of Ra = 225.3 g /mol