Chlorine exists as two isotopes 37 Cl and 35 Cl with masses of 36.97 amu and 34.

Question

Chlorine exists as two isotopes 37Cl and 35Cl with masses of 36.97 amu and 34.97 amu respectively.

Chlorine has an average mass of 35.45 amu. Which statement is corerct?

35Cl has approximately the same abundance as 37Cl

35Cl is more abundant in nature than 37Cl

37Cl is more abundant in nature than 35Cl

Nothing can be said about the abundances of 35Cl and 37Cl without more information.

The atomic mass on the periodic table for strontium is 87.62 amu. What does this mean?

It means that strontium contains 87 neutrons.

It means that strontium contains 49 neutrons.

It means that strontium exists as two isotopes; one greater than and one less than 87.62 amu.

It means that the majority of strontium found in nature has a mass of 87.62 amu.

It means that if we have only one atom of strontium, it will have a mass of 87.62 amu.

It means none of the above.

35Cl has approximately the same abundance as 37Cl

35Cl is more abundant in nature than 37Cl

37Cl is more abundant in nature than 35Cl

Nothing can be said about the abundances of 35Cl and 37Cl without more information.

Explanation / Answer

Part 1)

35Cl account for 75.53% of chorine and 37Cl account for 24.47% of chorine
Therefore, 0.7553 x 34.96885 + 0.2447 x 36.96590 = 35.45 amu
The atomic mass of Chlorine (35.45 amu) is close to 35 and therefore, 35Cl is the isotope with the greatest percent abundance.

Answer is 35Cl is more abundant in nature than 37Cl

Part 2)

The first statement

1) It means that strontium contains 87 neutrons

This is incorrect, since mass number = number of neutrons+number of protons

2) It means that strontium contains 49 neutrons.

This is incorrect. The mass number is a weighed average for the isotopes of Strontium. Without knowing the purticulat isotope we cannot determine the number of neutrons

3) It means that strontium exists as two isotopes; one greater than and one less than 87.62 amu

This is incorrect. Strontium has four stable naturally occuring isotopes.

4) It means that the majority of strontium found in nature has a mass of 87.62 amu.

This is also incorrect. The fractional mass number is a weighed average for the different percentage of isotopes.

5) It means that if we have only one atom of strontium, it will have a mass of 87.62 amu.

This is also incorrect, since fractional mass number is the weighed average for the different percentage of isotopes

Therefore, the sensible answer for this problem would be,

It means none of the above.

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