How many moles of tin atoms are in a pure tin cup with a mass of 38.1 g?
The mass of one molecule of tin is 39.3g.
Number of moles = Mass given / Molar mass
So in order to answer this question and find out the NUMBER OF MOLES, we need to find the MASS GIVEN - this is simply the mass given to you in the question, which is 39.3 grams of tin. We also need to know the MOLAR MASS, which is found in the left hand corner of the element. For tin [Sn] the molar mass is 118.710.
Sub both these into the formula to get:
Number of moles = 39.3 / 118.710...