Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of 19.81 mg terephthalic acid produces 41.98 mg CO2 and 6.45 mg H2O. If 0.262 mol of terephthalic acid has a mass of 43.5 g, determine the molecular formula for terphthalic acid.
would i convert these to grams, making it look like this?
.01981g--> .04198g CO2 + .00645g H2O
um the percent of carbon in CO2 is 27.29%
and Hydrogen is 11.19% then i multiply it to get the grams... but idk what to do after that
Right. You will then have grams C and grams H. Note that the problem did not tell you how much O was in the sample. You find that by
0.01981 g - g C - g H = g Oxygen.
Now find moles.
moles C = g C/12.01 = ??
moles H = g H/1.008 = ??
moles O = g O/16 = ??
Now you want to fine the ratio of the moles to each other in small whole numbers. The easy way to do that is to divide the smallest number by itself thereby making sure that is 1.000. Then divide the other numbers by the same small number and round to whole numbers (don't round too much; i.e., if you end up with x.5 multiply everything by 2; if by x.25 multiply everything by 4 etc). That will give you the empirical formula. Using the empirical formula mass you can determine the molecular formula. I'll leave that for you but you can check back if you need additional assistance.
To determine the molecular formula of terephthalic acid, you would need to calculate the empirical formula first and then find the molecular formula by determining the ratio of empirical formula mass to the molar mass of the compound.
1. Start by converting the given masses of CO2 and H2O to moles:
Mass of CO2 = 0.04198 g
Molar mass of CO2 = 12.01 g/mol + 2 * 16.00 g/mol = 44.01 g/mol
Moles of CO2 = 0.04198 g / 44.01 g/mol = 0.0009527 mol
Mass of H2O = 0.00645 g
Molar mass of H2O = 2 * 1.01 g/mol + 16.00 g/mol = 18.02 g/mol
Moles of H2O = 0.00645 g / 18.02 g/mol = 0.0003584 mol
2. Calculate the moles of carbon and hydrogen in the terephthalic acid:
Moles of carbon = moles of CO2 = 0.0009527 mol
Moles of hydrogen = 2 * moles of H2O = 2 * 0.0003584 mol = 0.0007168 mol
3. To find the mole ratio of carbon to hydrogen, divide the moles of each element by the smallest value:
Moles of carbon / Moles of hydrogen = 0.0009527 mol / 0.0007168 mol ≈ 1.33
4. Multiply the ratio obtained in step 3 by an appropriate number to get whole numbers:
In this case, multiplying by 3 gives 1.33 * 3 ≈ 4
Therefore, the empirical formula for terephthalic acid is CH4O.
5. Finally, to determine the molecular formula, you need to compare the empirical formula mass to the molar mass of the compound:
Empirical formula mass = 12.01 g/mol (C) + 1.01 g/mol (H) + 16.00 g/mol (O) = 29.02 g/mol
Molecular formula mass = 43.5 g/mol (given in the question)
Molecular formula mass / Empirical formula mass = 43.5 g/mol / 29.02 g/mol ≈ 1.5
The ratio is approximately 1.5, so multiply the empirical formula by 2 to get the molecular formula:
Molecular formula = 2 * empirical formula = 2 * CH4O = C2H8O2
Therefore, the molecular formula of terephthalic acid is C2H8O2.