Question

Suppose a new element named questinium has two isotopes. these isotopes are qu-297 (40.30%, 296.78 amu) and qu-301 (59.70%, 300.88 amu). what is the atomic weight of questinium, reported to the correct number of significant digits?

Answer 1

299.2 The atomic weight of the new element is simply the weighted average of the isotopes. So 0.4030 * 296.78 + 0.5970 * 300.88 = 119.60234 + 179.62536 = 299.2277 Now the number of significant digits is the same as the number of significant digits of the LEAST PRECISE DATUM. And that would be the percentages at 4 significant digits each. So the result needs to be rounded to 4 significant digits which is 299.2