Question

select the correct answer.
thallium consists of 29.5%tl-203 and 70.5%tl-205. what is the relative atomic mass of thallium?
a. 203amu
b. 204 amu
c. 203.5 amu
d. 205.3amu
e. 204.4 amu

Explanation:

Step1: Recall the formula for relative atomic mass

The relative atomic mass (\(A_r\)) of an element with isotopes is calculated by the weighted average of the masses of its isotopes, where the weights are the relative abundances of the isotopes. The formula is:
\(A_r=\sum (isotope\ mass\times relative\ abundance)\)

Step2: Convert percentages to decimals

The abundance of Tl - 203 is \(29.5\% = 0.295\) and the abundance of Tl - 205 is \(70.5\%=0.705\).

Step3: Calculate the contribution of each isotope

• Contribution of Tl - 203: \(203\times0.295 = 203\times0.295 = 59.885\)
• Contribution of Tl - 205: \(205\times0.705=205\times0.705 = 144.525\)

Step4: Sum the contributions

Add the two contributions together: \(59.885 + 144.525=204.41\approx204.4\) amu

Answer:

E. 204.4 amu