Question

calculate the average atomic mass for an unidentified element given the following;
isotope % abundance relative mass mass contribution
x-24 78.994 23.985041700 amu (1)(23.985041700 amu) = 2 amu
x-25 10.001 24.98583692 amu (3)(24.98583692 amu) = 4 amu
x-26 11.013 25.982592929 amu (5)(25.982592929 amu) = 6 amu
7 amu
from the periodic table the element must be 8
a. 11.013 b. 24.307 c. 2430.7 d. 0.11013 e. 0.10001
f. 0.78994 g. 18.946744 h. 2.861463 i. 2.498834 j. ne
k. na l. mg m. al n. si

Explanation:

Step1: Convert % to decimal for X-24

To find the mass contribution, we first convert the percentage abundance to a decimal by dividing by 100. For X-24, the % abundance is 78.994, so the decimal is $ \frac{78.994}{100} = 0.78994 $.

Step2: Calculate mass contribution for X-24

Multiply the decimal abundance by the relative mass. So, $ 0.78994 \times 23.985041700 \approx 18.946744 $ amu.

Step3: Convert % to decimal for X-25

The % abundance is 10.001, so the decimal is $ \frac{10.001}{100} = 0.10001 $.

Step4: Calculate mass contribution for X-25

Multiply the decimal abundance by the relative mass. So, $ 0.10001 \times 24.98583692 \approx 2.498834 $ amu.

Step5: Convert % to decimal for X-26

The % abundance is 11.013, so the decimal is $ \frac{11.013}{100} = 0.11013 $.

Step6: Calculate mass contribution for X-26

Multiply the decimal abundance by the relative mass. So, $ 0.11013 \times 25.982592929 \approx 2.861463 $ amu.

Step7: Sum the mass contributions

Add the three mass contributions: $ 18.946744 + 2.498834 + 2.861463 \approx 24.307 $ amu.

Step8: Identify the element

Looking at the periodic table, the element with an average atomic mass of approximately 24.307 amu is Magnesium (Mg).

Answer:

s (for each blank):

1. \( 0.78994 \) (Option F)
2. \( 18.946744 \) (Option G)
3. \( 0.10001 \) (Option E)
4. \( 2.498834 \) (Option I)
5. \( 0.11013 \) (Option D)
6. \( 2.861463 \) (Option H)
7. \( 24.307 \) (Option B)
8. \( \text{Mg} \) (Option L)