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 =]