Below is a question that was sent to my email by a local student that is preparing for Chemistry examination.
Question:
Gallium has a relative atomic mass of 69.8. If only two isotopes of gallium were found to have nucleon numbers 69 and 70 respectively, what is the percentage abundance of gallium-69 that occurs naturally?
A. 20%
B. 40%
C. 60%
D. 80%This will involve some simple mathematical manipulation after you understand the concepts of Isotope and Isotopic Abundance.
PS: Check out “Comments” below for suggested answers
Related Articles:
- O Level Chemistry: Isotopes
- O Level Chemistry: Qualitative Analysis / Preparing Salts / Precipitation
- O Level Chemistry: Energy Changes – Exothermic & Endothermic Reactions
- O Level Chemistry: Mole Concepts / Chemical Calculations
- O Level Chemistry: Catalysts / Ammonia / Organic Chemistry / Sulfuric Acid
My answer is A.
Let the percentage abundance be ‘x’.
(x/100 x 69) + (100-x)/100 x70 =69.8
(69x+7000-70x)/100 =69.8
69x +7000 -70x =6980
-x = -20
x =20
Therefore percentage abundance is 20%
Reply
Indeed the easiest way is to use algebra and let % abundance of Gallium-69 as X.
Using the formula to calculate Isotopic Abundance, you will get % abundance of
Gallium-69 to be 20%.
Well Done!
Sean
Reply
not able to understand the concept of mole.
plz help me out
Reply
thanks!! i finally understand how to approach these type of questions
Reply