Question

hydrogen is 99% ^1H, 0.8% ^2H. calculate its average atomic mass.

Answer 1

To calculate the average atomic mass of hydrogen based on its isotopic abundances, you can use the following formula:

\[
\text{Average atomic mass} = \sum ( \text{isotopic mass} \times \text{fractional abundance})
\]

Given:

- For \( ^1H \) (protium), the mass is approximately 1.00784 u and its abundance is 99% or 0.99.
- For \( ^2H \) (deuterium), the mass is approximately 2.01410 u and its abundance is 0.8% or 0.008.

Now, apply the values:

\[
\text{Average atomic mass} = (1.00784 \, \text{u} \times 0.99) + (2.01410 \, \text{u} \times 0.008)
\]

Calculating each term:

1. For \( ^1H \):
\[
1.00784 \, \text{u} \times 0.99 = 0.99776 \, \text{u}
\]

2. For \( ^2H \):
\[
2.01410 \, \text{u} \times 0.008 = 0.0161128 \, \text{u}
\]

Now, add these two results together:

\[
\text{Average atomic mass} = 0.99776 \, \text{u} + 0.0161128 \, \text{u} = 1.0138728 \, \text{u}
\]

Rounded to a reasonable number of significant figures, the average atomic mass of hydrogen is approximately:

\[
\text{Average atomic mass} \approx 1.014 \, \text{u}
\]