A newly discovered element, X, has two naturally occurring isotopes. 93.5 percent of the sample is an isotope with a mass of 268.9 u, and 6.5 percent of the sample is an isotope with a mass of 269.9 u. What is the weighted average atomic mass for this element?

268.5 u

269.0 u

269.4 u

269.8 u

Question

A newly discovered element, X, has two naturally occurring isotopes. 93.5 percent of the sample is an isotope with a mass of 268.9 u, and 6.5 percent of the sample is an isotope with a mass of 269.9 u. What is the weighted average atomic mass for this element?
 
268.5 u 

269.0 u 

269.4 u 

269.8 u

aaronq · Answer

a weighted average takes into account the abundance of each component.

$m_{average}=\Sigma (mass_i*Isotope_{abundance}$
$m_{average}=(268.9amu)*(0.935)+(269.9amu)*(0.065)$

aaronq · Answer

ps. i forgot to close the bracket

anonymous · Answer

So what would be the answer? Im so lost . @aaronq

aaronq · Answer

you just need to multiply each pair and then add them together (268.9)*(0.935)+(269.9)*(0.065) heres a calculator http://web2.0calc.com

asib1214 · Answer

atomic mass= % abundance of isotope 1 (mass of isotope1) +
                      % abundance of isotope 2 (mass of isotope 2) +....
Solution= 93.5% (268.9u) + 6.5% (269.9u)
           = 251.42+17.54
           = 268.96u

aaronq · Answer

round up  268.965 = 268.97

asib1214 · Answer

yep 268.965= 268.97