The mineral cassiterite is a compound of tin and oxygen. Chemical analysis of cassiterite shows that the mass percentages of tin, Sn, and oxygen, O, are 78.8% and 21.2%, respectively. Determine the formula of this compound.
I found the molar mass and correct equation SnO4.
Sn-118.71
O-64
Do I do 78.8/118.71? =.66
21.2/64=.33
.33/.33=1 O
.66/.33=2 Sn
1 to 2 molar ratio.
So is it Sn20?
Did I do this correctly?
The first part of what you did is confusing. Here is what you do.
Take 100 g sample which gives you
78.8 g Sn
21.2 g O
Convert to mols
78.8/118.71 = about 0.66
21.2/16 = about 1.32
Now find the ratio of the two to each other with the smaller number being no less than 1.00. The easy way to do that is to divide the smaller number by itself which assures that one of being 1.00.
0.66/0.66 = 1.000 Sn
1.32/0.66 = 2.00 O
Empirical formula is SnO2
To determine the formula of the compound, you need to find the ratio of tin to oxygen atoms in the compound, based on the given percentages.
First, convert the mass percentages to grams:
78.8% of Sn = 78.8g Sn
21.2% of O = 21.2g O
Next, determine the moles of each element using their molar masses:
Molar mass of Sn = 118.71g/mol
Molar mass of O = 16.00g/mol
Moles of Sn = 78.8g / 118.71g/mol = 0.664 mol Sn
Moles of O = 21.2g / 16.00g/mol = 1.325 mol O
Divide the moles by the smaller value to determine the molar ratio:
Sn:O = 0.664 mol Sn / (0.664 mol Sn) = 1
O:O = 1.325 mol O / (0.664 mol Sn) = 2
Therefore, the formula of the compound is SnO2, not SnO4. Each tin atom is bonded to two oxygen atoms, resulting in a 1:2 ratio.
To determine the formula of the compound cassiterite (SnO2), you did not calculate the molar ratios correctly. Let's go through the calculation step by step:
1. Calculate the number of moles of each element present in the compound:
- Tin (Sn): 78.8 g / 118.71 g/mol = 0.664 moles
- Oxygen (O): 21.2 g / 16.00 g/mol = 1.325 moles
2. Divide the moles of each element by the lowest number of moles (tin, in this case) to find the simplest ratio:
- Tin (Sn): 0.664 moles / 0.664 = 1
- Oxygen (O): 1.325 moles / 0.664 = 1.993 ≈ 2
So, the simplest ratio of tin to oxygen in cassiterite is 1:2. Therefore, the correct formula of cassiterite is SnO2.
You don't need to refer to the molar masses of individual atoms (Sn-118.71 and O-16.00) to determine the formula. The given mass percentages (78.8% and 21.2%) directly reflect the ratio of the elements in the compound.