Question

How many moles are in 25 grams of dihydrogen monoxide

Answer 1

25 g H2O* (1 mol H2O/ 18 g H2O)= 1.4 mol H2O.
 

Answer 2

If you'd like the full working, here it is:

I calculated this by using the formula triangle.

Mass

Number Formula
Of moles Mass

To calculate the number if moles in a substance, you need to divide the Mass by the Formula mass. You get the formula mass by adding the atomic masses of the elements in the compound together. In this situation, H2O, it would be two hydrogen molecules plus one oxygen molecule which is 2 + 16. This is because the atomic mass of Hydrogen is 1 and the atomic mass of Oxygen is 16.

Now that we have the Formula mass we can go ahead and do the calculation since we already have the Mass. You do as follows:

Mass divided by Formula mass which is in this case - 25 divided by 18

By doing this calculation you will get the answer which is 1.38 moles which can be rounded to 1.4

Hope this helps :)