Question

How do calculate the the following problems?

Note:
"v" signifies an upside down caret ^
v2 signifies the subscript of 2
v6 signifies the subscript of 6

Calculate each of the following:
A. number of Li atoms in 4.5 mol of Li
B. number of CO v2 molecules in 0.0180 mol of CO v2
C. Moles of Cu in 7.8 * 10^21 atoms of Cu
D. Moles of C v2 H v6 in 3.75 * 10^23 molecules of C v2 H v6

Answer 1

All of these can be solved by using unitary method.

A. `1` mol of Li `= 6.022 * 10^23` atoms.
hence, `5.4` mol Li `=5.4 * 6.022 * 10^23` atoms
`= 3.252 * 10^24` atoms.

B. `1` mol of `CO_2` `= 6.022 * 10^23` molecules.
Hence, `0.0180` mol of `CO_2` `= 0.0180 * 6.022 * 10^23` molecules.

C. `6.022 * 10^23` atoms Cu = `1` mol Cu.
`1` atom Cu = `1/(6.022*10^23)` mol Cu.
hence, `7.8 * 10^21` atoms of Cu = `7.8 * 10^21 * 1/(6.022*10^23)` mol Cu.

D. `6.022 * 10^23` molecules of `C_2H_6` = `1` mol `C_2H_6`.
`1` molecule of `C_2H_6` = `1/(6.022 * 10^23)` mol `C_2H_6`.
Hence, `3.75 * 10^23` molecules of `C_2H_6` = `3.75 * 10^23 * 1/(6.022 * 10^23)` mol `C_2H_6`.

I haven't bothered to do the complete calculations, you can do them yourself.