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 X - 24 % abundance to decimal

To use the percentage abundance in calculations, we divide by 100. So for X - 24 with 78.994% abundance, the decimal - form is $\frac{78.994}{100}=0.78994$. So, 1 = F.

Step2: Calculate X - 24 mass contribution

Multiply the decimal - form of abundance by the relative mass. $(0.78994)(23.985041700\ amu)\approx18.946744\ amu$. So, 2 = G.

Step3: Convert X - 25 % abundance to decimal

Divide the percentage abundance of X - 25 (10.001%) by 100. $\frac{10.001}{100}=0.10001$. So, 3 = E.

Step4: Calculate X - 25 mass contribution

Multiply the decimal - form of abundance by the relative mass. $(0.10001)(24.98583692\ amu)\approx2.498834\ amu$. So, 4 = I.

Step5: Convert X - 26 % abundance to decimal

Divide the percentage abundance of X - 26 (11.013%) by 100. $\frac{11.013}{100}=0.11013$. So, 5 = D.

Step6: Calculate X - 26 mass contribution

Multiply the decimal - form of abundance by the relative mass. $(0.11013)(25.982592929\ amu)\approx2.861463\ amu$. So, 6 = H.

Step7: Calculate average atomic mass

Add up the mass contributions of all isotopes: $18.946744 + 2.498834+2.861463 = 24.307041\ amu\approx24.307\ amu$. So, 7 = B.

Step8: Identify the element

Looking at the periodic table, an element with an average atomic mass of approximately 24.307 amu is Magnesium (Mg). So, 8 = L.

Answer:

1. F. 0.78994
2. G. 18.946744
3. E. 0.10001
4. I. 2.498834
5. D. 0.11013
6. H. 2.861463
7. B. 24.307
8. L. Mg