Level: introductory
Reference: Marie Curie, "Sur le poids atomique du radium," Comptes Rendus 135, 161-163 (1902). Marie Curie, Doctoral Thesis (1903); English translation published as Radioactive Substances (Philosophical Library: New York, 1961).
Notes: Marie Curie née Marja Sklodowska (1867-1934) was one of the founders of the study of radioactivity. Born in Warsaw, she moved to Paris to study at the Sorbonne. She is best known today for the discovery of radium and its isolation. This painstaking task, requiring years of patient work under laboratory conditions primitive even by late 19th-century standards and finally yielding a material so radioactive that it glows, contributed greatly to her heroic image. On the way to radium, she and her husband Pierre also discovered polonium. They named that element after her native Poland, which was partitioned at that time among the German, Austrian, and Russian empires.
She shared the Nobel Prize in Physics in 1903, the same year she completed her doctoral dissertation. She, her husband Pierre Curie, and Henri Becquerel, were awarded the prize for their pioneering work on radioactivity. She was awarded the 1911 Nobel prize in Chemistry for her work in the discovery and isolation of the element radium. The name Curie lives on in the periodic table and among scientific units: the discoverers of element 96 named it curium, and a standard unit of radioactivity is called the curie.
The fact that Marie Curie remains the only person to have won two Nobel Prizes in different sciences is sufficient testimony to the significance of her work and her place in the history of science. The fact that she did this work at a time when women were nearly non-existent in academic or industrial laboratories has given Curie nearly mythic status. Her achievements are so compelling that they captured the attention even of Hollywood (Madame Curie, 1943, starring Greer Garson). She is the female scientist nearly everyone can name.
This is a rather mundane exercise to be drawn from the work of such an accomplished and celebrated scientist. But careful and meticulous wet chemical analysis was an important part of her work.
Calculational note: The problem can be done just as well using molar masses of silver and chlorine from a modern periodic table. The result will differ from that shown here only in the fourth significant figure. Molar mass is a weighted average of isotopes. For elements (like radium) that have no stable isotopes, the source of the sample has an important effect on the molar mass. Curie's sample, derived from pitchblende, would have consisted mainly of the longest-lived isotope, 226Ra, a product of uranium decay, with a little bit of the next longest-lived isotope, 228Ra, a product of thorium decay.
Solutions: To download solutions, go to:
http://web.lemoyne.edu/giunta/classicalcs/curieRa.doc
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