How to find the empirical forumula (chemistry) ?

Question

What is the empirical formula for caffeine, ,it has 49.5% C, 5.15% H, 28.9% N, 16.5% O, molar mass is 195g/mol.

TY

Answer 1

Here goes:

C = 49.5%
H = 5.15%
N = 28.9%
O = 16.5%

Mr = 195g/mol

Divide each element percentage by its atomic mass:
C = 49.5/12 = 4.125
H = 5.15/1 = 5.15
N = 28.9/14 = 2.06
O = 16.5/16 = 1.03

Divide each ratio by the smallest one (1.03) and round to the nearest whole number:
C = 4.125/1.03 = 4
H = 5.15 / 1.03 = 5
N = 2.06/1.03 = 2
O = 1.03/1.03 = 1

Hence empirical formula: C4H5N2O with a molar mass of 97

But molecular mass of caffeine = 195

So to find the conversion factor 195/97 = 2 (nearest whole number)

So we can also find the molecular formula of caffeine = 2 x C4H5N2O = C8H10N4O2.

Answer 2

Assume that you have 100 grams of the compound. From the percent compositions, in 100 grams of the compound, you would have 49.5 g of carbon, 5.15 grams of hydrogen, 28.9 grams of nitrogen and 16.5 grams of oxygen.

Divide each of those masses by the respective atomic weights of each atom to convert the masses into moles. That will give you 4.125 moles C, 5.15 moles H, 2.06 moles N, and 1.03 moles oxygen. Next, divide all of those by the smallest, giving you a molar ratio of 4 C to 5 H to 2 N to 1 O. Those ratios are the ratios of the elements in the empirical formula:
C4H5N2O

The empirical formula has a mass of about 97. Since the molar mass of caffeine is 195, you can conclude that the molecular formula (NOT the empirical formula) is C8H5N4O2.

Answer 3

For ease of calculation, assume 100 grams total
divide the mass of each element by its atomic weight: 49.5/12.011, 5.15/1.008, 28.9/14.008, 16.5/16
and get 4.12, 5.109, 2.063, 1.03 (the ratios of C, H, N, and O respectively)
Find the least common denominator = 1.03
C=4.12/1.03=4
H=5.109/1.03=5
N=2.063/1.03=2
O=1.03/1.03=1
C4H5N2O is the empirical formula and the MW is 97
However, you were given that the MW was 195, so the molecular formula was 2x the empirical formula, or C8H10N4O2

Answer 4

it is percent to mass-
C 49.5% = 49.5g, etc
Mass to moles-
Convert the mass of the element to Moles using the molar mass of each element
49.5g divided by the molar mass of Carbon
etc.
Divide by small-
take the smallest amount of moles and divide each elements moles by that amount
Times til whole-
if you come up with a decimal find the number needed to make it a whole number and multiply the number of all the elements by that number.
the numbers you have left over are your emperical formula

to find the molecular formula you take the molar mass you have (195 g/mol) and divide it by the molar mass of the empirical formula. it will always be a whole number and then you multiply the empirical formula amounts by that number and there is your molecular formula!

Hope i helped!

Answer 5

1. If the empirical formula is HO it is correct to say H1O1. They have the same subscipts of 1. Therefore you can multiply those supcripts by any number. So look at your answers and which one has both of the subscripts the same? 2. You can figure out the name of Mg by looking at a periodic table. ClO is hypochlorite. So put the two together and you get your answer. 3. What are the Element symbols for Titanium and Carbon? Since they both have the same charge but one is positve and the other is negative then the subscripts are one for both elements. 4. 2H2 + O2 → 2H2O you have 4 moles of H2, 2 moles of O2 on the reactant side; you have 4 moles of h2, 2 moles of O2 on the product side; now you decide if it is true. 5.Fe3O4 + 4H2 → 3Fe + H2O You have 3 moles of Fe, 4 moles of O2, 8 moles of H2 on the reactant side; you have 3 moles of Fe, 1 mole of O2, 2 moles of H2 on the product side. decide if it is true. 6. CaC2 + 2H2O → Ca(OH)2 + C2H2 you have 1 mole of Ca, 2 moles of C, 4 moles of H2, 2 moles of O2; you have 1 mole of Ca; 2 moles of C, 4 moles of H2, 2 moles of O2; decide if it is true. 7. Based on the last three problems that I explained I think you should be able to figure out the last question. I did not give you direct answers because you should give them a try first. Sorry if you did not like my answers.

Answer 6

damn, i just finished chem lol and i cant remember without the equations. they are like n=mass of something/ molar mass and then empirical formula=(something)n. use ur book, sorry. if u provide the equations i could probably help.