Question

Which element has a mass percent composition of 21.49% in borax, Na2B4O7?

Answer 1

The element with a mass percent composition of 21.49% in borax (Na₂B₄O₇) is boron (B).

Step-by-step explanation:

Borax, chemically represented as Na₂B₄O₇, consists of sodium (Na), boron (B), and oxygen (O) atoms. To determine the element with a mass percent composition of 21.49%, we focus on the atomic mass of boron and its contribution to the overall molecular mass of borax.

The molecular formula indicates that one molecule of borax (Na₂B₄O₇) contains four boron atoms. To calculate the mass percent of boron, we use the formula:

`\[ \text{Mass Percent of Boron} = \frac{\text{Mass of Boron in One Molecule}}{\text{Molecular Mass of Borax}} * 100 \]`

Given that boron has an atomic mass of approximately 10.81 g/mol, the mass of boron in one molecule of borax is
`\(4 * 10.81\)` g/mol. The molecular mass of borax is the sum of the atomic masses of its constituent atoms:
`\(2 * \text{Na} + 4 * \text{B} + 7 * \text{O}\).`

After calculating these values, we find that the mass percent of boron in borax is indeed 21.49%, making boron the element in borax with the specified mass percent composition.

In summary, boron, with a mass percent composition of 21.49%, is the key element in borax, and this determination is based on the calculation of the mass percent using the atomic masses of boron and the other elements present in the borax molecule.


Complete Question:

Which element has a mass percent composition of 21.49% in borax (Na₂B₄O₇)?

Answer 2

Boron (B) has a mass percent composition of 21.49% in borax.

To find out which element in borax (Na₂B₄O₇) has a mass percent composition of 21.49%, we'll follow these steps:

1. Determine the Molar Mass of Borax:

Calculate the molar mass of Na₂B₄O₇ using the atomic masses of sodium (Na), boron (B), and oxygen (O).

2. Calculate the Mass Percent Composition of Each Element in Borax:

The mass percent of an element in a compound is calculated by the formula:

`\[ \text{Mass percent} = \left( \frac{\text{Mass of the element in one mole of the compound}}{\text{Molar mass of the compound}} \right) * 100\% \]`

3. Compare with the Given Percentage:

Compare the calculated mass percent composition of each element with 21.49% to find out which element matches this value.

Let's perform these calculations.

The molar mass of borax (Na₂B₄O₇) is approximately 201.21 g/mol. The mass percent composition of each element in borax is as follows:

- Sodium (Na): 22.85%

- Boron (B): 21.49%

- Oxygen (O): 55.66%

Comparing these values with the given percentage (21.49%), we can see that Boron (B) has a mass percent composition of 21.49% in borax.