A student sketches the mass spectrum of a metallic element Z on graph paper whose…
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A student sketches the mass spectrum of a metallic element Z on graph paper whose y-axis is labeled “Relative Abundance (%),” with gridlines every 10 %. From the sketch the following observations can be made:
• The peak at m/z = 24.0 reaches just under the 80 % gridline.
• The peak at m/z = 25.0 reaches almost exactly the 10 % gridline.
• The peak at m/z = 26.0 rises slightly above the 10 % gridline.
No other peaks are present.
Assume singly charged ions.
(a) Estimate the percent abundance of each isotope of element Z, clearly indicating any approximations you make.
(b) Using your abundances from part (a), calculate the average atomic mass of element Z. Express the result to three significant figures.
(c) Consult a periodic table and identify element Z. Discuss how closely your calculated average atomic mass agrees with the tabulated value and propose one experimental factor that could account for any discrepancy.
(d) Suppose a purified sample contained only the two heavier isotopes in a 1 : 1 number ratio. Predict the average atomic mass of such a purified sample and explain your reasoning.