gallium has an atomic mass of 69.723 amu. the ga-69 (68.926 amu) is 60.11%. what is the amu of the other isotope?

Question

jfraser · Answer

You know that the average atomic mass of any element is the weighted average of all of its isotopes. That makes an equation that looks like:$$Ga_{avg} = \%(^{69}Ga)*68.926amu + \%(^{xx}Ga)*(xx amu)$$
You know the percentage of Ga-69, so you also know the percentage of the other isotope, since the two must add to 100%. You also know the average mass. The only missing piece is the mass of the unknown isotope. Solve for that.$$69.723amu = (0.6011)(68.926amu) + (0.3989)(^{unk}Ga)$$ I'll tell you what I get later