[Illusory]

Hey guys,
I'm sure you can already sense my newbie vibes, so thanks to anyone who takes the time to give this the once over ^_^.

I was just looking for someone to check over my work and let me know if it's correct/point out the faults in my method.


"Work out the percentage abundance of the Gallium isotopes using the following information: -
Gallium: relative isotopic masses 68.95 and 70.95.
Relative atomic mass Ar = 69.72."

= r% of 68.95 plus (100% - r%) of 70.95 = 69.72
= (r ÷ 100 x 68.95) + (100 ÷ 100 x 70.95) – (r ÷ 100  x 70.95) = 69.72
= r x 0.6895 + 70.95 – r x 0.7095 = 69.72
= 0.6895r – 0.7095r + 70.95 = 69.72
= -0.02r + 70.95 = 69.72
= -0.02r = 69.72 - 70.95 = -1.23
= r = -1.23 ÷ -0.02 = 61.5

Isotopes of Gallium
Relative isotopic mass    % abundance
68.95                               61.5%
70.95                               38.5%


Thanks so much =]

[Padfoot]

Relative isotopic mass    % abundance
68.95                               61.5%
70.95                               38.5%

Perfect 

An easy way to check:
68.95 x 61.5% + 70.95 x 38.5% = 69.72

Completely missed this post...

[Illusory]

Thanks a lot =P. I'll definitely be using that simple little quick check in future (and not compare answers with classmates )
Again, thankyou!