Question

Question #a5eeb

Answer 1

2.13 moles of cobalt (II) cyanide weigh `"236 g"`.

In order to determine the weight of 2.13 moles of `Co(CN)_2` you must have an idea on how much 1 mole of this compound weighs. If you know how much 1 mole weighs, you know how much any number of moles weighs.

This is where the molar mass will come in handy. The molar mass of a compound is defined as the mass in grams occupied by exactly 1 mole of that compound.

Cobalt (II) cyanide's molar mass is 110.9 g/mol, which means that you can now determine the mass of 2.13 moles

`"2.13 moles" * "110.9 g"/"1 mole" = "236.22 g"`

Rounded to three sig figs, the answer will be

`m = "236 g"`

SIDE NOTE If the molar mass of cobalt (II) cyanide is not given to you, you can always calculate it by using the molar masses of the atoms that comprise this compound - 1 atom of cobalt, 2 atoms of carbon and 2 atoms of nitrogen - these values are available in the periodic table.

`M_m = M_(Co) + 2 * (M_C + M_N)`

`M_m = "58.9 g/mol" + 2 * ("12.0 g/mol" + "14.0 g/mol")`

`M_m = "110.9 g/mol"`