What is the molecular formula of ascorbic acid if its empirical formula?

Postby Joslyn_Santana_2B » Sat Sep 24, 2016 9:48 pm

Just realized this was covered in the video module.
Sorry about that, and thank you for taking your time with the explanation!

Page 2

Postby Joslyn_Santana_2B » Sat Sep 24, 2016 9:48 pm

Just realized this was covered in the video module.
Sorry about that, and thank you for taking your time with the explanation!

Page 3

If you know the percent composition and the molar mass of a compound, here's how you can determine its molecular formula.

A compound's molar mass tells you what the exact mass of 1 mole of that compound is. In your case, you know that ascorbic acid has a molar mass of 176.1 g/mol.

This means that 1 mole of ascorbic acid has a total mass of 176.1 g. Let's assume that you have a 176.1-g sample of ascorbic acid. According to ascorbic acid's percent composition, every 100 g of acid will contain 40.92 g carbon, 4.58 g hydrogen, and 54.50 g oxygen.

This means that your 176.1-g sample will contain

#176.1cancel("g") * "40.92 g C"/(100cancel("g")) = "72.06 g C"#

#176.1cancel("g") * "4.58 g H"/(100cancel("g")) = "8.065 g H"#

#176.1cancel("g") * "54.50 g"/(100cancel("g")) = "95.97 g O"#

To get the number of moles each element contributes to 1 mole of ascorbic acid, simply divide these numbers by each element's molar mass

#"For C": (72.06cancel("g"))/(12.0cancel("g")/"mol") = 6.005 ~= 6#

#"For H": (8.065cancel("g"))/(1.01cancel("g")/"mol") = 7.985 ~= 8#

#"For O": (95.97cancel("g"))/(16.0cancel("g")/"mol") = 5.998 ~= 6#

Therefore, the molecular formula of ascorbic acid is

#C_6H_8O_6#

One mole of ascorbic acid contains 6 moles of carbon, 8 moles of hydrogen, and 6 moles of oxygen.

Yes,the molecular and empirical formulae of one substance can be same.