Determine the empirical and molecular formulas for vanillin given that its molar mass is 152 g/mole and its
composition is: 63.15% carbon, 5.30 % hydrogen and the rest oxygen
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To determine the empirical and molecular formulas for vanillin, we need to start by calculating the empirical formula.
Step 1: Convert the percentages to grams.
Mass of carbon = 63.15% of 152 g/mole = 95.838 g
Mass of hydrogen = 5.30% of 152 g/mole = 8.056 g
Mass of oxygen = (100% - (63.15% + 5.30%)) of 152 g/mole = 48.106 g
Step 2: Convert the masses to moles.
Moles of carbon = 95.838 g / atomic mass of carbon = 95.838 g / 12.01 g/mole = 7.983 mol
Moles of hydrogen = 8.056 g / atomic mass of hydrogen = 8.056 g / 1.01 g/mole = 7.98 mol
Moles of oxygen = 48.106 g / atomic mass of oxygen = 48.106 g / 16.00 g/mole = 3.01 mol
Step 3: Find the simplest whole number ratio.
Divide the moles of each element by the smallest number of moles (in this case, 3.01).
Moles of carbon = 7.983 mol / 3.01 mol = 2.65 ≈ 3
Moles of hydrogen = 7.98 mol / 3.01 mol = 2.65 ≈ 3
Moles of oxygen = 3.01 mol / 3.01 mol = 1
The empirical formula for vanillin is C3H3O.
To determine the molecular formula, we need the molar mass of vanillin.
Step 4: Calculate the molar mass of the empirical formula.
Molar mass of C3H3O = (3 * atomic mass of carbon) + (3 * atomic mass of hydrogen) + atomic mass of oxygen
Molar mass of C3H3O = (3 * 12.01 g/mole) + (3 * 1.01 g/mole) + 16.00 g/mole
Molar mass of C3H3O = 36.03 g/mole + 3.03 g/mole + 16.00 g/mole
Molar mass of C3H3O = 55.06 g/mole
Step 5: Divide the molar mass of vanillin by the molar mass of the empirical formula.
Molar mass of vanillin / molar mass of C3H3O = 152 g/mole / 55.06 g/mole
Molar mass of vanillin / molar mass of C3H3O = 2.76
Step 6: Multiply the subscripts of the empirical formula by the ratio found in step 5 to get the molecular formula.
Molecular formula = (C3H3O)2.76
Therefore, the empirical formula for vanillin is C3H3O and the molecular formula is (C3H3O)2.76.
To determine the empirical and molecular formulas for vanillin, we need to analyze its composition and molar mass.
1. Convert the percentages to grams:
Given that the composition of vanillin is 63.15% carbon, 5.30% hydrogen, and the rest oxygen, assume we have 100 grams of vanillin. Therefore, we have:
- Carbon: 63.15 g
- Hydrogen: 5.30 g
- Oxygen: 100 g - (63.15 g + 5.30 g) = 31.55 g
2. Determine the number of moles of each element:
To do this, we need to calculate the number of moles by dividing the mass of each element by their respective atomic masses.
- Carbon:
Number of moles of carbon = mass of carbon (g) / atomic mass of carbon (g/mol) = 63.15 g / 12.01 g/mol ≈ 5.26 mol
- Hydrogen:
Number of moles of hydrogen = mass of hydrogen (g) / atomic mass of hydrogen (g/mol) = 5.30 g / 1.01 g/mol ≈ 5.25 mol
- Oxygen:
Number of moles of oxygen = mass of oxygen (g) / atomic mass of oxygen (g/mol) = 31.55 g / 16.00 g/mol ≈ 1.97 mol
3. Divide each number of moles by the smallest number of moles:
To find the simplest, whole-number ratio of the atoms, we divide each of the above numbers of moles by the smallest number of moles (in this case, 1.97 mol).
- Carbon: 5.26 mol / 1.97 mol ≈ 2.67 ≈ 3 (rounded to the nearest whole number)
- Hydrogen: 5.25 mol / 1.97 mol ≈ 2.66 ≈ 3 (rounded to the nearest whole number)
- Oxygen: 1.97 mol / 1.97 mol = 1
4. Write the empirical formula:
Based on the ratio obtained in the previous step, the empirical formula of vanillin is C3H3O.
5. Determine the molecular formula using the molar mass:
To find the molecular formula, we need to compare the empirical formula mass to the molar mass given.
- Empirical formula mass:
The empirical formula mass can be calculated by adding the atomic masses of all the atoms in the empirical formula:
Empirical formula mass = (atomic mass of carbon × number of carbon atoms) + (atomic mass of hydrogen × number of hydrogen atoms) + (atomic mass of oxygen × number of oxygen atoms)
Empirical formula mass = (12.01 g/mol × 3) + (1.01 g/mol × 3) + (16.00 g/mol × 1) = 37.05 g/mol
- Determine the molecular formula:
To obtain the molecular formula, divide the molar mass of the compound by the empirical formula mass and multiply the subscripts in the empirical formula.
Molecular formula = (molar mass of vanillin) / (empirical formula mass)
Molecular formula = 152 g/mol / 37.05 g/mol ≈ 4.10
Since we cannot have fractional subscripts in a chemical formula, we need to round the value obtained. Multiplying all the subscripts by 5, we get:
Molecular formula = C15H15O5
Therefore, the empirical formula of vanillin is C3H3O and its molecular formula is C15H15O5.
63.15 % Carbon
5.30 % Hydrogen
100 - (63.15+5.30) = 31.55 % Oxygen
To do this, divide each mass percentages with the corresponding weights of the elements to get the moles of each:
63.15 / 12 = 5.26
5.30 / 1 = 5.30
31.55 / 16 = 1.97
Now, divide all by the smallest, in this case, by 1.97,
5.26 / 1.97 = 2.67
5.30 / 1.97 = 2.69
1.97 / 1.97 = 1
Then multiply each by their atomic weights, and add:
(2.67 * 12) + (2.69 * 1) + (1 * 16) = 50.73
Then divide the given mass by the sum:
152 / 50.73 = 2.996
Finally, we multiply this by the empirical number of moles of each:
C: 2.67*2.996 = 7.99932, which is approximately 8
H: 2.69*2.996 = 8.059, which is approximately 8
O: 1*2.996 = 2.996, which is approximately 3
Therefore, vanillin is C8H8O3.
Hope this helps~ :)