Answer:
[tex]\boxed {\boxed {\sf A. \ 12.5 \ grams}}[/tex]
Explanation:
We are asked to find the mass of 2.34 × 10²³ atoms of sulfur (S)
First, we convert atoms to moles using Avogadro's Number of 6.022 × 10²³. This is the number of particles (atoms, molecules, formula units, etc.) in 1 mole of a substance. For this question, the particles are atoms of sulfur. There are 6.022 × 10²³ atoms of sulfur in 1 mole of sulfur.
We will convert using dimensional analysis, so we must set up a ratio.
[tex]\frac {6.022 \times 10^{23} \ atoms \ S}{1 \ mol \ S}[/tex]
We are converting 2.34 × 10²³ atoms of sulfur to moles, so we multiply the ratio by this value.
[tex]2.34 \times 10^{23} \ atoms \ S* \frac {6.022 \times 10^{23} \ atoms \ S}{1 \ mol \ S}[/tex]
Flip the ratio so the units of atoms of sulfur cancel.
[tex]2.34 \times 10^{23} \ atoms \ S* \frac{1 \ mol \ S} {6.022 \times 10^{23} \ atoms \ S}[/tex]
[tex]2.34 \times 10^{23}* \frac{1 \ mol \ S} {6.022 \times 10^{23}}[/tex]
[tex]\frac{2.34 \times 10^{23}} {6.022 \times 10^{23}} \ mol \ S[/tex]
[tex]0.3885752242 \ mol \ S[/tex]
Next, we convert moles to grams using the molar mass. This is the mass of 1 mole of a substance. The value is found on the Periodic Table as the atomic mass, but the units are grams per mole instead of atomic mass units. Look up sulfur's molar mass.
Set up another ratio.
[tex]\frac {32.07 \ g \ S}{ 1\ mol \ S}[/tex]
Multiply by the number of moles we calculated.
[tex]0.3885752242 \ mol \ S *\frac {32.07 \ g \ S}{ 1\ mol \ S}[/tex]
The units of moles of sulfur cancel.
[tex]0.3885752242 *\frac {32.07 \ g \ S}{ 1}[/tex]
[tex]0.3885752242 * {32.07 \ g \ S}[/tex]
[tex]12.46160744 \ g \ S[/tex]
The original value of atoms (2.34 × 10²³) has 3 significant figures (2,3, 4), so our answer must have the same. For the number we calculated, that is the tenths place. The 6 in the hundredth place tells us to round the 4 up to a 5.
[tex]12.5 \ g \ S[/tex]
There are 12.5 grams of sulfur in 2.34 × 10²³ atoms of sulfur.
