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?
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
