Question

How many moles are in 68 grams of copper (II) hydroxide, `Cu(OH)2`?

Answer 1

There are `0.70` moles of `Cu(OH)_"2"`.

Explanation:

We can use the following formula to determine the number of moles:

`m=nM`

where:
m = mass (grams)
n = number of moles
M = molar mass

To find the number of moles, we first have to find the molar mass of `Cu(OH)_"2"`. We can do this by adding the molar masses of copper, oxygen, and hydrogen together, accounting for the number of atoms for each element.

`M_color(brown)"copper"=color(brown)((63.55g)/(mol))`

`M_color(blue)"hydrogen"=(1.01g)/(mol)*2=color(blue)((2.02g)/(mol))`

`M_color(green)"oxygen"=(16.00g)/(mol)*2=color(green)((32.00g)/(mol))`

`M_color(purple)"copper (II) hydroxide"=color(brown)((63.55g)/(mol))+color(blue)((2.02g)/(mol))+color(green)((32.00g)/(mol))=color(purple)((97.57g)/(mol))`

Now we can substitute our known values into the formula to solve for number of moles:

`m=nM`

`n=m/M`

`n=68g-:color(purple)((97.57g)/(mol))`

`n=68g*(mol)/(97.57g)`

`n=68color(red)cancelcolor(black)(g)*(mol)/(97.57color(red)cancelcolor(black)(g))`

`n=(68mol)/97.57`

`n=0.6969355335 mol`

`n=0.70mol`

Note:
The final answer should always have the correct number of significant figures.

`:.`, there are `0.70` moles of `Cu(OH)_"2"`.