A naturally occurring sample of the element boron has a relative atomic mass of 10.8 In this sample, boron exists as two isotopes. Calculate the percentage abundance of 10B in this naturally occurring sample of boron.
The answer is 20%. This is a failry common question and stomps many students.
The easiest way to answer this question, in my opinion, is to see that this question is asking you to figure out the ratio of isotopes. Looking at the number 10.8 we can see that for every 8 11Bs we have 2 10Bs and so (2/8+2)*100 = 20%
Another way of looking at it is by showing an average of the percentage abundaces and making them equate to 10.8.
10x/100 + 11(100–x)/100 = 10.8
10x + 1100 – 11x = 1080
∴ x = 1100 – 1080 = 20%
TA
Related Chemistry A Level answers
All answers ▸The intermolecular interactions between halogen molecules are Van der Waals' forces. Explain how these Van der Waal's forces arise between halogen molecules.
Why is CO2 a linear molecule whereas H2O has a v-shaped geometry?
An amino acid contains 52.2% carbon, 9.3% hydrogen, 8.7% nitrogen and 29.8% oxygen by mass and has a relative molecular mass of 161 g/mol. What is its molecular formula? What functional groups must it have?
A student reacts 50.0cm^3 of 2.00mol dm^-3 HCl with 25.0cm^3 NaOH. What is the concentration of NaOH?