Question

Question #d0c80

Answer 1

The thimble contains `3.3 * 10^(-4)` moles of water.

To go from number of molecules to moles and vice versa, you can use Avogadro's number, which describes the number of atoms or molecules present in a mole of substance.

According to this, each mole contains exactly `6.022 * 10^(23)` atoms or molecules; in your case, 1 mole of water would contain `6.022 * 10^(23)` molecules of water.

Since `2.0 * 10^(20)` is a smaller number than `6.022 * 10^(23)`, you'll have less than 1 mole of water in a thimble.

The exact value is

`2.0 * 10^(20)cancel("molecules") * "1 mole"/(6.022 * 10^(23)cancel("molecules")) = 3.321* 10^(-4)"moles"`

Rounded to two sig figs, the answer will be

`color(green)(3.3 * 10^(-4)"moles of water")`

Answer 2

The thimble contains `3.3xx10^(-4)` moles of water.

`1 "mole water molecules" = 6.022xx10^23 "water molecules"`

`2.0xx10^20 cancel ("water molecules")xx(1 "mole water molecules")/(6.022xx10^23 cancel ("water molecules")` = `3.3xx10^(-4) "moles water molecules"`