If you weighed 5.0 grams of PLA, how many moles of LA monomer residues do you have?
To determine the number of moles of LA monomer residues in 5.0 grams of PLA (polylactic acid), we need to use the molar mass of lactic acid (LA) and the formula weight of PLA.
Here are the necessary steps to calculate the number of moles:
1. Find the molar mass of lactic acid (LA). The molar mass of lactic acid is approximately 90.08 g/mol. It can be calculated by adding the atomic masses of each element in the compound: C₃H₆O₃.
- Carbon (C) has an atomic mass of approximately 12.01 g/mol.
- Hydrogen (H) has an atomic mass of approximately 1.01 g/mol.
- Oxygen (O) has an atomic mass of approximately 16.00 g/mol.
So, the molar mass of lactic acid is: (3 * 12.01) + (6 * 1.01) + (3 * 16.00) = 90.08 g/mol.
2. Determine the formula weight of PLA. The empirical formula of PLA is (C₆H₄O₂)n, where n represents the number of repeating units. The formula weight of PLA can be calculated by multiplying the molar mass of lactic acid by the number of repeating units. Therefore, the formula weight of PLA is 90.08 g/mol * 2 = 180.16 g/mol (assuming there are two repeating units of lactic acid in PLA).
3. Calculate the number of moles of PLA. To do this, divide the mass of PLA by its formula weight. In this case, the mass is 5.0 grams.
Number of Moles = Mass (in grams) / Formula Weight (in grams per mole)
Number of Moles = 5.0 g PLA / 180.16 g/mol PLA = 0.0277 moles
Therefore, if you weighed 5.0 grams of PLA, you would have approximately 0.0277 moles of LA monomer residues.