Gallium is composed of two naturally occurring isotopes: Ga-69 (60.108%) and Ga-71 . The ratio of the masses of the two isotopes is 1.0290. What is the mass of Ga-69

Question

aaronq · Answer

atomic mass = $\Sigma (i_{\%abundance}*Ga^{i})$

atomic mass = % abundance(1) * isotope(1) +% abundance(2) * isotope(2)+....

tgoddard · Answer

I have the values of Ga-69 as .618511, and Ga-71 as .410489, the percent for Ga-71 is 39.892%. I keep getting 1.029 for the mass of Ga-69. Using this, I came up with .618511 g. I know I am doing something wrong...

aaronq · Answer

sorry i misread the question  

ratio =  1.0290 = $\dfrac{Ga^{71}}{Ga^{69}}$

are you allowed to use the actual molar mass of Ga?

aaronq · Answer

1.029*$Ga^{69}=Ga^{71}$

69.723 amu = 60.108% $Ga^{69}$+ (41.0489%)*1.029*$Ga^{69}$

aaronq · Answer

i got x=68.1239150124833732

tgoddard · Answer

Yes we can use actual molar mass

aaronq · Answer

do you understand what i did above?

tgoddard · Answer

I think so, give me a second to run some numbers with it

tgoddard · Answer

the second percentage is supposed to be 39.892 I believe

aaronq · Answer

sorry, you're right about that, i copied the numbers you posted earlier. So yeah, change that in the equation.

tgoddard · Answer

Thank you

aaronq · Answer

no problem