Citric acid, the compound responsible for the sour taste of lemons, has the following elemental composition: C, 37.51%; H, 4.20%; O, 58.29%. Calculate the empirical formula of citric acid.
so i did that and got C6H8O7 but now i need to find the molecular formula and i know you have to find 'n' by dividing the mass of the compound by the mass of the empirical formula.
so the mall of the ef is 192g. they didn't give me a mass of the compound so should i assume its 100g??
i did that and get 'n' to be like .5 but you can't multiply the ef by .5 to get the molecular formula because 'n' has to be a whole number right??
what am i doing wrong?
No, assuming the mass is 100 g is not the way to go. You MUST have some more information in the problem. One way is to give information for elevation of boiling point or depression of freezing point to determine the molar mass of the compound. For gases the problem often gives density; of course this is not a gas. What other information is given in the problem?
What does mall of the ef mean? That's the information you need.
192/192 = 1 so n = 1
To find the molecular formula of citric acid, you first need to calculate the empirical formula, which you correctly determined to be C6H8O7.
Now, to find the molecular formula, you need to know the molar mass of citric acid. Unfortunately, the question does not provide the exact mass of the compound. Assuming it to be 100g might not necessarily be accurate, as the molar mass could vary.
To proceed, you'll need to know the molar mass of the empirical formula, which you calculated to be 192g.
Divide the molar mass of the compound by the molar mass of the empirical formula:
Molar mass of compound / Molar mass of empirical formula = n
For now, let's consider that you obtained n as 0.5.
However, you correctly pointed out that n should ideally be a whole number to get the molecular formula. In this case, 0.5 does not provide a whole number.
This indicates that your assumption for the molar mass of the compound (100g) might not be accurate. You need to find the correct molar mass of the compound to proceed further.
To find the molar mass of the compound, you can use experimental data or additional information. If you have the compound's molar mass, you can re-calculate n by dividing the actual molar mass by the empirical molar mass.
Once you have the correct value of n, round it to the nearest whole number (if it's not already a whole number) and multiply the subscripts of each element in the empirical formula by this value to get the molecular formula.