The ionic compund sometimes called yellow uranium is used to produce colored glazes for ceramics. It is 7.252% sodium, 75.084% uranium, and 17.664% oxygen
a. What is the empirical formula for this compound?
b. This compound has a molecular mass of 1268.06 g/mol, what is the molecular compound for this formula?
Take 100 g sample which gives you
7.252 g Na
75.084 g U
17.664 g O
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convert to mols by mols = grams/atomic mass.
7.252/23 = approx 0.315
75.084/238 = approx 0.315
17.664/16 = approx 1.10
For the empirical formula you want to find the ratio of these elements to each other with the smaller whole number being 1.00. The easy way to do that is to divide the smallest number by itself (thereby assuring 1.00 for that element) then divide the other numbers by the same small number.
If I do that I have
0.315/0.315 = 1.00 for Na
0.315/0.315 = 1.00 for U
1.10/0.315 = 3.5 for O. Since we want whole numbers it is easy to see that multiplying everything by 2 will give whole numbers (we do that INSTEAD of rounding that 3.5 to either 3.0 or 4.0) so the empirical formula is Na2U2O7.
Empirical formula mass is ? you can add it up.
Then empirical formula x n = molar mass
Plug in empirical formula mass, plug in molar mass of 1268, solve for n, round to a whole number, and the molecular formula is (Na2U2O7)n and n will be 1 or 2 or 3 etc.
make a table such as this, assume you have 1000 grams of the stuff.
read om four columns: element/mass/moles/ratio
Na/ 72.52 / 3.12
U/ 750.84/3.02
O / 176.64/11.04
Now, for the last column, pick the lowest number in mole column (here 3.02) and divide it into the other numbers.
Na: 1
U: 1
O : 3.65
Now the simplest whole number ration
Na: 2
U: 2
O: 7
empirical: Na2U2O7
empirical x(2*23+2*238+7*16)=1268
x(634=1268
x=2
mol formula= Na4U4O14
To determine the empirical formula, we need to find the simplest whole number ratio of the elements in the compound. Here's how you can calculate it:
a. First, convert the percentages into grams. We assume we have 100g of the compound for simplicity.
- Sodium (Na): 7.252g
- Uranium (U): 75.084g
- Oxygen (O): 17.664g
b. Next, calculate the number of moles for each element:
- Moles of Na = Mass of Na / Molar mass of Na = 7.252g / 22.989g/mol = 0.315 mol
- Moles of U = Mass of U / Molar mass of U = 75.084g / 238.028g/mol = 0.315 mol
- Moles of O = Mass of O / Molar mass of O = 17.664g / 16.00g/mol = 1.104 mol
c. Find the smallest ratio of the moles by dividing through the smallest number of moles:
- Moles of Na:Moles of U: Moles of O = 0.315:0.315:1.104
- Divide through by 0.315 to get the ratio: 1:1:3.5
d. Multiply all the numbers by 2 to get whole numbers:
- The ratio becomes 2:2:7
e. Write the empirical formula using the elements' symbols:
- The empirical formula is Na2U2O7
Now, to determine the molecular formula, we need the molar mass of the empirical formula and the given molecular mass:
Molar mass of Na2U2O7 = (2 × molar mass of Na) + (2 × molar mass of U) + (7 × molar mass of O)
= (2 × 22.989g/mol) + (2 × 238.028g/mol) + (7 × 16.00g/mol)
= 45.978g/mol + 476.056g/mol + 112.00g/mol
= 634.034g/mol
To find the molecular formula from the empirical formula, divide the given molecular mass (1268.06 g/mol) by the molar mass of the empirical formula (634.034 g/mol):
Molecular formula = (Molecular mass) / (Empirical formula mass)
= 1268.06 g/mol / 634.034 g/mol
≈ 2
Therefore, the molecular formula for the empirical formula Na2U2O7 is a multiple of 2. The molecular formula is Na4U4O14.