Question

How many molecules of water are present in 7.8 moles of water? (1 point)
Responses

4.7 x 1024 molecules
4.7 x 1024 molecules

6.022×1023 molecules
6.022×1023 molecules

4.69 molcules
4.69 molcules

7.8 x 1023 molecules

Answer 1

To calculate the number of molecules present in 7.8 moles of water, you can use Avogadro's number, which is \(6.022 \times 10^{23}\) molecules/mole.

Now, multiply the number of moles by Avogadro's number:

\[
\text{Number of molecules} = 7.8 \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mole}
\]

Calculating this gives:

\[
7.8 \times 6.022 \approx 46.94
\]

Now multiply by \(10^{23}\):

\[
46.94 \times 10^{23} = 4.694 \times 10^{24} \, \text{molecules}
\]

So, rounding this to two significant figures gives approximately:

\[
4.7 \times 10^{24} \, \text{molecules}
\]

Thus, the correct response is:

**4.7 x 10²⁴ molecules**.