Answer Happy

How many grams of AgBr would have been formed from 0.100 g of
RaBr2? (Answer: 0.097 g)
Marie and Pierre Curie and Henri Becquerel shared the Nobel Prize in Physics in 1903 for pioneering investigations of radioactivity. The Curies needed four years to isolate 100 mg of RaCl, from several tons of ore. Marie received the Nobel Prize in Chemistry in 1911 for her isolation of metallic radium. Linus Pauling, John Bardeen, and Frederick Sanger are the only others who received two Nobel Prizes. EXAMPLE Marie Curie's Measurement of the Atomic Mass of Radium In her Ph.D. research (Radioactive Substances, 1903), Marie Curie measured the atomic mass of radium, which she discovered. From its chemical properties, she knew that radium is in the same family as barium, so the formula of radium chloride is RaCl. When 0.091 92 g of pure RaCl, was dissolved and treated with excess AgNO3, 0.088 90 g of AgCl precipitated. How many moles of I were in the RaCl ? From this measurement, find the atomic mass of Ra. Solution AgCl precipitate weighing 0.088 90 g contains 0.088 90 g Aget 143.321 g Aget/mol AgCl 6.202, X 10-4 mol AgCI Because 1 mol of AgCl contains 1 mol of Cl", there must have been 6.202, X 10 * mol of Cl in the RaCl. For 2 mol of Cl, there must be 1 mol of Ra, so 6.202, X 10-4 met Et mol radium = = 3.1014 x 10-4 mol 2 mel et/mol Ra 752 CHAPTER 27 Gravimetric and Combustion Analysis Let the formula mass of RaCl, be x. We found that 0.091 92 g RaCl, contains 3.1014 X 10 * mol Racly. Therefore 0.091 92 g RaCl2 3.1014 X 104 mol RaCl = x g RaCl/mol RaCl2 0.091 92 g RaCl2 = 296.38 g/mol 3.1014 10-4 mol RaCl2 The atomic mass of Cl is 35.452, so the formula mass of RaCl, is Formula mass of RaCl2 = atomic mass of Ra + 2(35.452 g/mol) = 296.38 g/mol → atomic mass of Ra = 225.5 g/mol x = The inside cover of this book lists the atomic number (the integer mass) of the long-lived isotope of Ra, which is 226. TEST YOURSELF How many grams of AgBr would have been formed from 0.100 g of RaBr? (Answer: 0.097 g)