Question

calculate the number of atoms in 100.0g of mercury:

Part 3: Average Mass:

Atomic Mass = (0.1687 X 198.968254) + (0.2310 X 199.968300) + (0.1318 X 200.970277) + (0.2986 X 201.970617) = 166.35 amu

Isotope: ¹⁹⁹Hg, 198.968254 amu, 16.87 % abundance

Isotope: ²⁰⁰Hg, 199.968300 amu, 23.10 % abundance

Isotope: ²⁰¹Hg, 200.970277 amu, 13.18 % abundance

Isotope: ²⁰²Hg, 201.970617 amu, 29.86 % abundance

Part 4: Use the average mass calculated in Part 3 to calculate the number of atoms in 100.0g of mercury:

1 amu = 1.66 X 10^-24g

100.0 g X (1 amu/ 1.66 X 10 ^-24) X (1 atom Mercury / 166.35 amu) = 3.62 X 10²³
This is what i did but I dont think it is right.

Answer 1

Four isotopes are given. The sum of the percent abundance of these four isotopes is % which is not 100. So the calculated value of 166.35 amu for average atomic mass is incorrect. The correct value should be between 199 to 202 amu.

We need the data (percent abundance and atomic mass) for fifth isotope also so that we can calculate correct value for the average atomic mass.

If the data for fifth isotope is not available, then we can proceed with less accurate calculation which is given below.

The average atomic mass

Now we can proceed with calculation

Hence, the number of Hg atoms in 100.0 g of sample are