Question #0b2e8

1 Answer
Mar 12, 2015

The first thing you must do is determine exactly how much acetic acid you get from 25.0 g of vinegar.

Now, you could eyeball it and say that, because vinegar is 5% acetic acid, 25 grams of vinegar would have 4 times less acetic acid than 100 g of vinegar, which means you get roughly 1.25 g of acetic acid to work with (because 100 g of vinegar would have 5 g of acetic acid).

However, vinegar is 5% acetic acid by volume, which means you get 5 g of acetic acid per 100 mL of vinegar. Since vinegar has a density of 1.01 g/mL, that mass of vinegar would have a volume of

25.0 g vinegar1 mL1.01 g=24.75 mL vinegar

Using the 5% percent concentration by volume you know you have, that much volume of vinegar would contain

24.75 mL vinegar5 g acetic acid100 mL vinegar=1.2375 g acetic acid

To determine how many molecules of acetic acid are present in that many grams, you need to figure out how many moles you have; this is done by using acetic acid's molar mass of 60.05 g/mol

1.2375 g1 mole60.05 g=0.0206 moles acetic acid

Because 1 mole of any substance contains exactly 6.0221023 molecules of that substance - this is know as Avogadro's number- the number of molecules of acetic acid will be

0.0206 moles6.0221023molecules1 mole=1.241022molecules

SIDE NOTE If you were supposed to use vinegar's 5% acetic acid concentration as being by mass, use the 1.25 g mass as a starting point to figure out the number of moles first, and then the number of molecules.