1)Naturally occuring boron is made up of 20% by mass of 10B isotope and 80% by mass of 11B isotope.Calculate the relative atomic mass of boron. (2)Natural Silicon containing ores contains 92% of 28Si, 5% of 29Si and 3% of 30Si.Calculate the relative atomic mass of Silicon.
(0.2*10) + (0.8*11) = mass B.
To be accurate you should have the masses of 10B and 11B given and plug those values in instead of 10 and 11.
To calculate the relative atomic mass of an element, we need to consider the abundance of each isotope of that element and their respective atomic masses.
1) For boron:
Given that naturally occurring boron consists of 20% by mass of the 10B isotope and 80% by mass of the 11B isotope.
Step 1: Determine the atomic masses of the isotopes.
The atomic mass of 10B is approximately 10 amu.
The atomic mass of 11B is approximately 11 amu.
Step 2: Calculate the contribution of each isotope to the average relative atomic mass.
Percentage of 10B isotope = 20%
Contribution of 10B = 20% × 10 amu
Percentage of 11B isotope = 80%
Contribution of 11B = 80% × 11 amu
Step 3: Calculate the average relative atomic mass of boron by summing up the contributions of each isotope.
Average atomic mass = Contribution of 10B + Contribution of 11B
So, in this case, the relative atomic mass of boron is:
(20% × 10 amu) + (80% × 11 amu) = 2 amu + 8.8 amu = 10.8 amu
Therefore, the relative atomic mass of boron is approximately 10.8 amu.
2) For silicon:
Given that natural silicon containing ores consist of 92% of 28Si, 5% of 29Si, and 3% of 30Si.
Step 1: Determine the atomic masses of the isotopes.
The atomic mass of 28Si is approximately 28 amu.
The atomic mass of 29Si is approximately 29 amu.
The atomic mass of 30Si is approximately 30 amu.
Step 2: Calculate the contribution of each isotope to the average relative atomic mass.
Percentage of 28Si isotope = 92%
Contribution of 28Si = 92% × 28 amu
Percentage of 29Si isotope = 5%
Contribution of 29Si = 5% × 29 amu
Percentage of 30Si isotope = 3%
Contribution of 30Si = 3% × 30 amu
Step 3: Calculate the average relative atomic mass of silicon by summing up the contributions of each isotope.
Average atomic mass = Contribution of 28Si + Contribution of 29Si + Contribution of 30Si
So, in this case, the relative atomic mass of silicon is:
(92% × 28 amu) + (5% × 29 amu) + (3% × 30 amu) = 25.76 amu + 1.45 amu + 0.9 amu = 28.11 amu
Therefore, the relative atomic mass of silicon is approximately 28.11 amu.