Strontium (Sr, atomic number 38, average atomic mass = 87.62) naturally exists as 4 stable isotopes with masses of 84, 86, 87, and 88. Which statement is correct?
· Strontium-87 is the most abundant.
· All strontium isotopes are equally abundant.
· Strontium-86 is the most abundant.
· Strontium-88 is the most abundant.
The Correct Answer and Explanation is :
The correct statement is:
Strontium-88 is the most abundant.
Explanation:
Strontium (Sr) exists naturally as a mixture of four stable isotopes: Sr-84, Sr-86, Sr-87, and Sr-88. The atomic mass of strontium is 87.62, which is the weighted average of the masses of these isotopes based on their natural abundance. This indicates that the most abundant isotope of strontium must have a mass close to the average atomic mass of 87.62, which aligns with Sr-88.
Let’s break down the isotopes of strontium:
- Strontium-84 (Sr-84) has a mass of 84 and is one of the isotopes of strontium. It is not the most abundant, as its presence in nature is less compared to Sr-88.
- Strontium-86 (Sr-86) has a mass of 86 and is also naturally present but not in the highest quantity.
- Strontium-87 (Sr-87) has a mass of 87 and is radioactive, decaying from rubidium-87. However, it is relatively less abundant compared to Sr-88. The existence of Sr-87 is important in applications like radiometric dating but does not contribute the most to the natural strontium isotopic composition.
- Strontium-88 (Sr-88) has a mass of 88 and is the most abundant isotope of strontium. It accounts for about 82.6% of the naturally occurring strontium. This is consistent with the fact that the atomic mass of strontium is closer to 88 than to 87.
The average atomic mass of strontium (87.62) is calculated based on the weighted average of the isotopic masses and their relative abundances. Since Sr-88 is the most abundant isotope, it heavily influences this average, making it closest to its mass. Therefore, the statement that Sr-88 is the most abundant is correct.
Conclusion:
The most abundant isotope of strontium is Sr-88, which accounts for the largest portion of strontium found in nature, and it contributes significantly to the average atomic mass of 87.62.