The formula for sulfur tetrafluoride is SF4.
a. How many grams of sulfur are present in 3.90 moles of sulfur tetrafluoride? grams
b. How many moles of fluorine are present in 4.21 grams of sulfur tetrafluoride? moles
The correct answer and explanation is :
Part A: How many grams of sulfur are present in 3.90 moles of sulfur tetrafluoride (SF₄)?
Solution:
To calculate the grams of sulfur present in 3.90 moles of SF₄, we first need to determine the molar mass of sulfur tetrafluoride (SF₄).
The molar mass of SF₄ is calculated by adding the atomic masses of sulfur (S) and fluorine (F):
- Atomic mass of sulfur (S) = 32.07 g/mol
- Atomic mass of fluorine (F) = 18.998 g/mol
The formula SF₄ tells us that there is one sulfur atom and four fluorine atoms in one molecule of SF₄. So, the molar mass of SF₄ is:
$$
Molar\ mass\ of\ SF_4 = 32.07\ g/mol\ (S) + 4 \times 18.998\ g/mol\ (F)
$$
$$
Molar\ mass\ of\ SF_4 = 32.07\ g/mol + 75.992\ g/mol = 108.062\ g/mol
$$
Now, to find the grams of sulfur in 3.90 moles of SF₄, we use the following conversion:
$$
\text{Grams of sulfur} = 3.90\ moles\ SF_4 \times \left( \frac{32.07\ g}{1\ mol\ SF_4} \right)
$$
$$
\text{Grams of sulfur} = 3.90 \times 32.07 = 125.47\ g
$$
So, 125.47 grams of sulfur are present in 3.90 moles of sulfur tetrafluoride.
Part B: How many moles of fluorine are present in 4.21 grams of sulfur tetrafluoride (SF₄)?
Solution:
We need to first find how many moles of SF₄ are in 4.21 grams, and then convert that into moles of fluorine atoms.
- Calculate moles of SF₄:
We use the molar mass of SF₄, which we already determined to be 108.062 g/mol. Now, we can convert grams of SF₄ into moles:
$$
\text{Moles of SF}_4 = \frac{4.21\ g}{108.062\ g/mol} = 0.03898\ mol
$$
- Convert moles of SF₄ to moles of fluorine (F):
Since each SF₄ molecule contains 4 fluorine atoms, the number of moles of fluorine is 4 times the number of moles of SF₄. So,
$$
\text{Moles of fluorine} = 0.03898\ mol\ SF_4 \times 4 = 0.15592\ mol
$$
Therefore, 0.156 moles of fluorine are present in 4.21 grams of sulfur tetrafluoride.
Explanation:
For both parts, we used basic stoichiometric relationships and the molar mass of the compounds involved to convert between grams and moles. In part A, the key step was using the molar mass of sulfur and applying it to the number of moles of SF₄. In part B, the moles of SF₄ were first determined from the given mass, and then the number of moles of fluorine was calculated based on the molecular formula SF₄, where each SF₄ molecule contains 4 fluorine atoms. This problem is an application of fundamental concepts in stoichiometry, utilizing molar masses to convert between mass, moles, and atoms of different elements.