Problem 25P

How many moles of tin atoms are in a pure tin cup with a mass of 38.1 g?

Solution 25P

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

Number of moles = 0.331058883

We are not finished - remember to round of the lowest amount of significant figures found in the working of the question. In the working out, which was (39.3 / 118.71) the 39.3 has 3 significant figures and the 118.70 has 5 significant figures. ALWAYS TAKE THE LOWEST AMOUNT FOUND. The lowest amount is 3, so we must round this answer to 3 significant figures.

It will be: 0.331

Therefore, 0.331 moles of tin atoms are in a pure tin cup with a mass of 39.3.