To do this, you would first add together the molar mass of all involved elements, to find how many grams are in a mole of Cu(OH)2. Keep in mind, the molar mass is equal to the atomic mass of an element in grams. For example the molar mass of copper (Cu) would be 63.55 (with 2 sig. figs.)
Therefore, now we add together the mass of all elements involved.
Cu: (63.55)+O2(15.99x2=31.98)+H2(1.01x2=2.02)
63.55+31.98+2.02= 97.55g per mole of Cu(OH)2.
Now, divide what we have by how much it takes to get a mole of the stuff.
68.1/97.55= 0.698mol Cu(OH)2
