What is the molar mass of Al(NO3)3 · 3H2O?

Go to your periodic table and look for each element. Find the mass for Aluminum, Nitrogen, Oxygen, and Hydrogen.

After you find those, for each compound you must add them together and find the least amount of sig figs after the decimal point.

For the first compound, Al(NO3)3, you will have a total of

1 Aluminum atom

3 Nitrogen atoms

9 Oxygen atoms

Aluminum has 26.982 g/mol

Nitrogen has 14.007 g/mol

Oxygen has 15.999 g/mol

Now multiply those numbers by the amount of atoms of each element.

(1)26.982 g/mol = 26.982 g/mol

(3)14.007 g/mol = 42.021 g/mol

(9)15.999 g/mol = 143.991 g/mol

now add all of those numbers together, and you see that their least significant figure after the decimal is 3, so round to 3 digits after the decimal point.

26.983 + 42.021 + 143.991 = 212.994

now do the same for the other compound

to start you off.. you have

6 Hydrogen atoms

3 Oxygen atoms

Hydrogen has 1.009 g/mol

Oxygen has 15.999 g/mol

the least significant figure after the decimal point is 3, so round you 3 digits after the decimal point.

after you finish getting your totals, you. until them and find the greatest sig fig over all. comment on this if you need further instruction :)