Question

The element boron, a trace element in Earth's crust, is found in foods produced from plants. Boron has only two naturally occurring stable isotopes, boron-10 and boron-11. One sample of a green vegetable contains 0.0035 gram of boron. Determine the total number of moles of boron in this sample.

Answer 1

The answer to your question is: 0.00032 moles of Boron

Step-by-step explanation:

Boron AM = 10.81 g

Mass = 0.0035 g in the sample

Rule of three

10.81 g of Boron ----------------- 1 mol

0.0035 g ------------------ x

x = (0.0035 x 1) / 10.81

= 0.00032 moles

Answer 2

Number of moles ≈ 0.000324 moles

Step-by-step explanation:

The question is to calculate the number of moles in the sample.

We were given;

mass = 0.0035g

The relationship between mass and number of moles;

Mass = Number of moles * Molar Mass

Since the element occurs in isotopes, we have to calculate it''s average molar mass;

About 19.9% of all boron atoms are boron-10 with a mass of 10.0129 amu, and the remaining 80.1% are boron-11 with a mass of 11.0093 amu. The average atomic mass for boron is calculated to be:

boron average mass = (0.199×10.0129amu) + (0.801×11.0093amu)

= 1.99amu + 8.82amu = 10.81 amu

It is important to understand that no single boron atom weighs exactly 10.8 amu; 10.8 amu is the average mass of all boron atoms, and individual boron atoms weigh either approximately 10 amu or 11 amu.

Inserting back into the formular;

Number of moles = Mass / Molar mass

Number of moles = 0.0035 / 10.81

Number of moles = 0.000324 moles