Check your answer...do you agree? Great if you do. If you do not check the Solution: below the table to see how the number of atoms, molecules or formula units is calculated.

Formula

M , Molar Mass

(g­mol-1)

mass of sample

(g)

n, number of

moles of sample

N, number of atoms,

molecules or formula units

unknown

119

56.8

0.476

  2.87 x 1023 f.u.

Solution:

We are to calculate the number of atoms, molecules or formula units of the unknown in the sample. First we need to know whether we are calculating atoms, molecules or formula units in this case. Since the exact nature of the substance is unknown we can not know exactly. So we will go with formula units. That is the most general term and works here. Since we know the moles of the unknown in the sample we can determine the number of formula units using Avogadro's number,

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