[govibe]

1) Only one isotope of this element occurs in nature. One atom of this isotope has a mass of 9.123 x 10-23 g. Identify the element and give its atomic mass.

I'm not sure how to do this because we are not given any conversions between grams and moles...

Question 2) A compound containing only sulfur and nitrogen is 69.6% S by mass; the molar mass is 184 g/mol. What are the empirical and molecular formulas of the compound? (Type your answer using the format CO2 for CO2.)

Again, I'm not sure how to do this problem because we don't know the molar masses of each sulfur and nitrogen... Can someone explain these two problems?

[Borek]

I'm not sure how to do this because we are not given any conversions between grams and moles...

What is Avogadro number?

Again, I'm not sure how to do this problem because we don't know the molar masses of each sulfur and nitrogen...

Look them up in periodic table.

[Quantum07]

For number 1 I believe I would do this.

You know the mass of the atom to be 9.123 x 10 ^-23 g

One mole of atoms will give you the element's atomic mass so multiply avogadro's number times the mass of the atom.

You get 54.95 g/mol which is the elements Mn. If you look up Mn on www.webelements.com and click on Mn then on the left under NMR Properties you will see NATURALLY OCCURING ISOTOPES you will see that Mn has only one which is ⁵⁵Mn that is 100%.

To confirm this is correct divide the atom's mass by the mass of the proton and you will indeed get 55 as the number of protons.


For number 2.

A % means out of 100 so you make an assumption. You assume you have 100 grams of the compound that is formula S_xNy.

Simply make the percents to grams.

69.6% S ----> 69.6g S  The rest of the percent has to be Nitrogen so 100-69.6= 30.4%
30.4%N ---->  30.4g N

Divide the mass of each atom by the atomic mass of the element

69.6g S / 32.06g/mol S = 2.17 moles S
30.4g N / 14.01g/mol N=  2.17 moles N

You would typically divide by the smallest number of moles in order to get the smallest whole number ratio but since each elements has the same number in this case it doesn't matter.

2.17 mol S / 2.17 mol S=  1 mol S
2.17 mol N/ 2.17 mol S=   1 mol of N

The ratio of S to N is 1:1 so the empirical formula is 1:1.

To get the molecular formula first you need to find the empirical formula's weight

32.07 g/mol S + 14.01 g/mol N = 46.08g/mol

The molecular weight is 184g/mol so in order to get the molecular formula you need to divide by the empirical formula's weight.

184/46= 4....The molecular weight is 4 times the empirical formula so it becomes S₄N₄