How many moles of cobalt(II) cyanide are in a #"2.05 g"# sample?

1 Answer
Meave60
Mar 2, 2015

In order to determine the number of moles in a sample of a substance, you need to first determine its chemical formula. Then, using the chemical formula, you need to determine its molar mass, which is the mass of one mole of the substance. Then multiply the given mass times #"1 mol"/"molar mass"#.

The chemical formula of cobalt II cyanide is #"Co(CN)"_2"#

Determine the molar mass of cobalt II cyanide, #"Co(CN)"_2"#.
Co: 1 x 58.933 g/mol = 58.993 g/mol
C: 2 x 12.011 g/mol = 24.022 g/mol
N: 2 x 14.007 g/mol = 28.014 g/mol
Molar mass of #"Co(CN)"_2"# = 110.97 g/mol

Multiply the given mass times #"1 mol"/"molar mass"# for #"Co(CN)"_2"#.

#"2.05 g"# x #"1 mol"/"110.97 g/mol"# = #"0.0185"# #"mol"# #"Co(CN)"_2"# (three significant figures due to 2.05 g)

Note: You can also divide the given mass by the molar mass, but I think it's easier to do the multiplication because it's easy to see how grams are canceled, leaving moles.

#"2.05 g"/"110.97 g/mol"# = #"0.0185"# #"mol"# #"Co(CN)"_2"#

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