Question

Determine the number of moles in 258.45 grams of iron (III) chloride (FeCl3). Show and explain all

your work for full credit. Make sure you show all units.

Answer 1

`\boxed {\boxed {\sf 1.5935 \ mol \ FeCl_}}`

Step-by-step explanation:

To convert from grams to moles, we must use the molar mass. This can be found on the Periodic Table. First, find the molar mass of iron and chlorine.

• Fe: 55.84 g/mol
• Cl: 35.45 g/mol

Check the formula. There is a subscript of 3 after Cl, so there are 3 atoms of chlorine in 1 molecule. Multiply iron's molar mass by 3, then add iron's molar mass.

• FeCl₃: 55.84 + 3(35.45) = 55.84+106.35=162.19 g/mol

Use this number as a ratio.

`\frac {162.19 \ g\ FeCl_3}{1 \ mol \ FeCl_3}`

Multiply by the given number of grams.

`258.45 \ g \ FeCl_3 *\frac {162.19 \ g\ FeCl_3}{1 \ mol \ FeCl_3}`

Flip the ratio so the grams of iron (III) chloride cancel.

`258.45 \ g \ FeCl_3 *\frac {1 \ mol \ FeCl_3}{162.19 \ g\ FeCl_3}`

`258.45 *\frac {1 \ mol \ FeCl_3}{162.19}`

`\frac {258.45 \ mol \ FeCl_3}{162.19}`

`1.59350144892 \ mol \ FeCl_3`

The original measurement of grams has 5 significant figures, so our answer must have the same. For the number we calculated, that is the ten thousandth place.

`1.5935 \ mol \ FeCl_3`

258.45 grams is approximately 1.5935 moles of iron (III) chloride.