<p>This questions seems easy to solve, but I am clueless. </p>
<p>Magnesium is commonly extracted from seawater. Magnesium-24 is its most abundant isotope (78.90%); its exact mass is 23.985 amu. If the atomic weight of magnesium is 24.305 amu, what are the relative abundaces of magnesium-25 (mass of 24.986 amu) and magnesium-26 (mass of 25.983 amu)?</p>
<p>… very little. There has to be an isotope thats less than 24.watever if the AMU is 23-something.</p>
<p>It’s asking for relative abundances… [very little] : [very little] doesn’t help lol</p>
<p>Plus the amu for that isotope is 23-something, not for the whole element.</p>
<p>It would be something like {(78.90<em>23.985)+(x</em>24.986)+(y*25.983)}/100 = 24.305</p>
<p>Solve for x/y</p>
<p>I’m not sure though… haven’t done much chem/math in the last 2 months. :(</p>
<p>Edit: Plus you know y=21.1-x (b/c it adds up to 100%).</p>
<p>Let x be the abundance of magnesium-25.</p>
<p>24.305 = (0.789)(23.985) + 24.986x + (1-0.789-x)(25.983)</p>
<p>Solve for x. Abundance of magnesium-25 = 100x %</p>
<p>Abundance of magnesium-26 = 100(1-0.789-x) %</p>
<p>I got x = 0.101883651.</p>