Question

What is the MASS of a `0.0118*mol` quantity of water?

Answer 1

By definition, `"moles of stuff"="mass of stuff"/"molar mass of stuff"`

Explanation:

And you will use this quotient continuously in chemistry....given TWO of the three parameters, we can calculate the third....here we gots the molar quantity, and we know that the molar mass of water is given by...

`underbrace(16.00*g*mol^-1+2xx1.00794*g*mol^-1)_"molar masses of atomic oxygen and hydrogen"=18.01*g*mol^-1`

Now the question specifies a `0.0118*mol` quantity; to get the mass of this molar quantity, we takes the product....

`0.0118*cancel(mol)xx18.01*g*cancel(mol^-1)=0.213*g`

And note the dimensional consistency of the answer. We wanted an answer with units of mass, and the calculation gave us an answer in grams as required. You can often use dimensional analysis in these sorts of problems as a check against multiplying when you should be dividing, and vice versa. It is all too easy to ballz up a question.

So how many oxygen atoms, and how many hydrogen atoms are in this mass of water?