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This is tangentially related to question 10 on this week's homework, but I couldn't figure out how to read the diagram to find out the chemical formula of the 2-butanone so I just googled the molar mass. I'm assuming we won't be allowed to do this on exams, though, so is this something we'll go over later, or has it been covered already and I just missed it?
This was my biggest question from this week as well. I used the internet to find the necessary numbers to complete the problem, but was wondering if it was possible to do it any other way. If anyone has any insight it would be greatly appreciated!
With organic molecules such as the ones shown in Question 10, the “zig-zag” line refers to bonds between carbon atoms and each vertex including the points at either end of the zig-zag represents a single carbon atom. Since carbon can from 4 bonds, in organic molecules it is assumed that carbon fills its 4 bonds with hydrogen atoms unless otherwise shown (as in the case of the OH in 3‑methyl‑3‑hexanol, and the Br in 1‑bromopropane). This means vertices in the zig-zag of carbon atoms would also have bonds to 2 hydrogen atoms unless another element/atom/organic group is shown. Additionally, single carbon atoms at the end points of the zig-zag would be bonded to 3 hydrogen atoms as they are depicted to have one bond with another carbon to make the carbon chain. Double bonds and Triple bonds would be shown with additional lines between molecules (i.e. the two lines indicating a double bond between the O and the carbon in 2-butanone and the alternating double lines depicted in the chemical structure drawing of a benzene ring). The molar mass can be found by figuring out the number of carbons and hydrogens in the carbon chain based on the number of additional bonds formable by the carbon atoms and multiplying by their respective molar masses. Also, add the molar mass of any other organic group, or element bonded to the chain (i.e. organic acid (COOH), Br, O, OH, COO).
I recall Professor Lavelle stating that on exams, you will be given either the molar mass of the molecule or the molecular formula in order to find the molar mass (or the mass of each element in the molecule, either in percentages or grams).
The structure in that problem can be read as though each point between lines that doesn't have a letter associated with it is a carbon atom. Then, depending on the number of bonds each carbon atom has, you add enough hydrogens to each carbon atom to make a total of four bonds.
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