How do I derive the emperical and molecular formula for the compound?

Question

A sample of a compound containing C,O, and silver (Ag) weighed 1.372g. On analysis it was found to contain 0.288g O and 0.974g Ag. The molar mass of the compound is 308.8g/mol.

Answer 1

1) you can find the percent composition of the C, O, and Ag in the compound (i.e. % O = massO/massTotal=0.288g/1.372g=Y)
*Y*100% being the percent oxygen. Do this for the rest of the elements.

2) now that you've done this, you have the percent composition of each element in grams. Since the empirical formula is the ratio of the various elements, in moles, divide each percentage by its molecular weight (g/mol from periodic table). This will give the relative mole ratios of the elements in the compound.

3) now divide each molar amount by the lowest of the three molar amounts. This will give the ratio of each element present in the compound. This is your empirical formula. NOTE: THE RATIOS MUST BE WHOLE NUMBERS. if they are not, multiply them by like 2 or 3 or what ever it takes to get them to be whole numbers. you can round like 2.1 to 2 or 2.9 to 3 but you cannot round like 3.5 or 3.6.

4) To determine the molecular formula, you first find the total weight of the empirical formula. Then you solve the below expression:

(weight_empirical formula)*x=weight_molecular formula

x should then be an integer number. The molecular formula is the empirical formula multiplied by this number.

ex. if empirical formula is C2OAg and x = 2, molecular formula would be C4O2Ag2. THIS IS JUST AN EXAMPLE

Answer 2

Silver Molecular Weight

Answer 3

First find the mass of C

mass of C = 1.372 - 0.288 - 0.974 = 0.11 g

Then calculate the moles of each substance dividing each mass with the Atomic Weight of the element:

Ag: 0.974/108 = 9*10^(-3) mol
C: 0.11/12 = 9*10^(-3) mol
O: 0.288/16 = 18*10^(-3) mol

Now divide by the smallest value:

Ag: 9*10^(-3)/9*10^(-3) = 1 mol
C: 9*10^(-3)/9*10^(-3) = 1 mol
O: 18*10^(-3)/9*10^(-3) = 2 mol

So the empirical formula is: (AgCO2)v

Evaluate the molar mass:

Mr = (108 + 12 + 2*16)v = 152v

But Mr = 308, so 152v = 308, v = 2 approx. So the molecular formula of the substance is:

Ag2C2O4 (probably is the silver oxalic salt: AgOOC-COOAg)

Answer 4

you must find how many mole each weight of your elements contains by dividing the weight by molecular weight,, then after you get that you must know the ratio by dividing each mole by the smallest mole value you got,, so that can give you the emperical formula of your compound,, then you must know the emperical formula wieght by adding the formula weights of each element and divide the molar mass by the value you got ,,that can show you the ratio between molar mass and emperical formula and this ratio value must multiply by the number of atoms in your emperical formula so you can have the molecular formula of your molecule