How many moles of Al(CN)3 are in 165 g of the compound?

Question

How many moles of Al(CN)3 are in 165 g of the compound?

Answer 1

Hi Joana!

I recommend watching my video, but if you learn better from reading, here's my best synopsis:

To find the number of moles of Al(CN)3 ("Aluminum Cyanide") in 165g of the substance, we first need to find the molar mass of Al(CN)3. That is, how many grams are in one mole of Al(CN)3.

Al(CN)3 is basically just 1 aluminum atom, 3 carbon atoms, and 3 nitrogen atoms hanging out in a specific shape. So, to find the molar mass of Aluminum Cyanide, let's just add up the molar masses of all of its components.

Form the periodic table, we have:

Al = 26.982g/mol

C = 12.011g/mol

N = 14.007g/mol

so the molar mass of Aluminum Cyanide is:

1(Al) + 3(C + N)

= 1( 26.982 ) + 3( 12.011 + 14.007 )

= 26.982 + 3( 26.018 )

= 26.982 + 78.054

= 105.036 g/mol

Nice! Now, we just need to go back to our original question: How many moles of a 105.036g/mol substance do we have if the sample is 165g?

We can divide 165 by 105.036 to find our answer: 1.570889 moles! ∴

Let's take a closer look at those units, though:

165g / 105.036g/mol

We have grams divided by grams divided by moles! That's a headache. But, remember from Algebra that a number in the denominator of the denominator can be moved to the numerator!

so g / g / mol is the same as g·mol / g

our grams cancel, and we are left with just moles in the numerator.