If an isotope has a mass of only 47% of this standard, what is the mass? If an isotope has a mass of 250% of this standard, what is the mass? Explain.The element carbon (12) is used as the standard...

If an isotope has a mass of only 47% of this standard, what is the mass? If an isotope has a mass of 250% of this standard, what is the mass? Explain.

The element carbon (12) is used as the standard for all of the atomic masses of all of the isotopes of all of the elements on the periodic table. This question is talking about atomic mass based on the element carbon and the unit amu.

1 Answer | Add Yours

ncchemist's profile pic

ncchemist | eNotes Employee

Posted on

Carbon-12 is one of the most important isotopes in the entire periodic table.  It is used to define both the concept of the mole and also the atomic mass unit.  A mole by definition is the number of atoms contained in twelve grams of pure C-12.  Thus, a mole is equal to 6.022 x 10^23 units.  We commonly use moles to describe amounts of chemicals but we could also use it to describe amounts of any types of things.  One mole of feathers would be 6.022 x 10^23 feathers.  In this sense, the concept of the mole is no different than calling 12 of any item a dozen, just on a much larger scale. 

C-12 is also used to define an atomic mass unit.  An atomic mass unit (also called a Dalton) is defined as exactly 1/12 the mass of a single atom of C-12.  This is approximately equal to 1.66 x 10-27 kg.  So if a particular isotope has a mass 47% of the C-12 standard, then the mass is 1.66 x 10^-27 * 0.47 = 7.802 x 10^-28 kg.  If a particular isotope has a mass 250% of the C-12 standard, then the mass is 1.66 x 10^-27 * 2.50 = 4.15 x 10^-27 kg.

We’ve answered 318,966 questions. We can answer yours, too.

Ask a question