 Conversions Mass - Mole - Numbers

Avogadro's number, the mole concept, formul weights and molar mass allow us to convert among masses, moles and number of atoms or molecules. For example suppose we have 25 g of acetic acid (C2H4O2). The molar mass of acetic acid is 60 g/mol. we can ask the following questions for 25 g of acetic acid:

• How many moles of acetic acid is this?
• How many moles of carbon ?
• How many moles of hydrogen ?
• How many moles of oxygen ?
• How many total moles of atoms ?
• How many carbon atoms ?
• How many hydrogen atoms ?
• How many oxygen atoms ?
• How many total atoms ?
• We can answer these questions in the following way:

 How many moles of acetic acid? = 25 g x (1 mol acetic acid/60 g) = 0.417 mol How many moles of carbon? = 2x0.417 mol = 0.834 mol of C How many moles of hydrogen? = 4x0.417 mol = 1.67 mol of H How many moles of oxygen? = 2x0.417 mol = 0.834 mol of O How many total moles of atoms? = 8x0.417 mol = 3.34 mol of atoms How many carbon atoms? = 0.834 mol x(6.022x10^+23/mol) = 5.02x10^+23 C atoms How many hydrogen atoms? = 1.67 mol x(6.022x10^+23/mol) = 1.01x10^+24 C atoms How many oxygen atoms ? = 0.834 mol x(6.022x10^+23/mol) = 5.02x10^+23 O atoms How many total atoms? = 3.34 mol x(6.022x10^+23/mol) = 2.01x10^+24 total atoms

Alternatively, we could have started with a number of molecules, and then convert this number to number of C atoms, mass of C atoms, moles of C atoms, total moles etc.. The procedure for this calculation is similar to that above..

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C101 Class Notes
Prof. N. De Leon   