Naturally occurring cobalt consists of only one isotope, cobalt59, whose relative atomic mass is 58.9332. A synthetic radioactive isotope of cobalt60, relative atomic mass 59.9338, is used in radiation therapy for cancer. A 1.8155 sample of cobalt has an apparent "atomic mass" of 58.9901.

I have to find Cobalt60 the mass.

See your post above.

To find the mass of Cobalt-60, we need to use the concept of weighted average atomic mass.

The weighted average atomic mass is calculated using the masses and relative abundances of different isotopes. In this case, we have the following information:

Naturally occurring Cobalt consists only of Cobalt-59.
- Relative atomic mass of Cobalt-59: 58.9332

Cobalt-60 is a synthetic radioactive isotope used in radiation therapy for cancer.
- Relative atomic mass of Cobalt-60: 59.9338

The problem gives the apparent "atomic mass" of a 1.8155 g sample of Cobalt as 58.9901.

To find the mass of Cobalt-60, we can assume the difference between the apparent atomic mass and the actual atomic mass comes from Cobalt-60. The mass of Cobalt-60 can be calculated as follows:

1. Calculate the mass of the naturally occurring isotope (Cobalt-59):
Mass of Cobalt-59 = 1.8155 g - mass of Cobalt-60

2. Find the difference between the apparent atomic mass and the atomic mass of Cobalt-59:
Difference = Apparent Atomic Mass - Atomic Mass of Cobalt-59

3. Substitute the values into the equation:
Difference = (1.8155 g - mass of Cobalt-60) - 58.9332

4. Rearrange the equation to solve for the mass of Cobalt-60:
Mass of Cobalt-60 = 1.8155 g - Difference + 58.9332

5. Substitute the values and calculate the mass of Cobalt-60.

Please note that the provided specific values are necessary to get the exact mass of Cobalt-60.