How do you determine the formula mass of a compound?

Answer 1

If you use an IR spectra you can determine the functional groupd of the compound,(hydroxyl, ester, ketones, etc.)After which, using the NMR spectra you can determine the strcuture of the hydrocarbon part of the compound (whether rings, double bonds, etc.)

Answer 2

It's very easy. First of all we test the given sample in laboratory to know about its constitution. Let's discuss it by taking an example:-

Suppose the constitution of a compound is given as below:-

C = 92.4%, H = 7.6%

let's assume that the sample is 100 gram. so the weight of carbon is 92.4 gram & that of hydrogen is 7.6 gram. Now it's we must make sure that is the total of weights of constituents 100 or not? If it is not 100, it means there is an another element in the compound, and this is always oxygen in case of hydrocarbons.

Step 1st :- Find out the number of moles of each element

number of moles = weight of the element/Atomic Mass

number of moles of C = 92.4/12 = 7.7 moles

number of moles of H = 7.6/1 = 7.6 mole

Step 2nd:- Find out the relative ratio of the moles:- It is simply done by dividing all by the smallest one

C = 7.7/7.6 = 1.01

H = 7.6/7.6 = 1

Step 3rd:- If the ratio is not whole numbers the multiply all the numbers by a smallest integer number to make them whole numbers.

Here in this case both are nearly whole numbers. so there is need to multiply these numbers.

C = 1

H = 1

Step 4th:- Write the empirical formula

C1H1

step 5th:- Find the weight of empirical formula

1*12 + 1*1 = 13

now if the molecular weight is given then the molecular formula can be written easily.

molecular weight = ( empirical formula weight)n

for example the molecular weight is 78.

n = 78/13 = 6

so the molecular formula is = C6H6

Answer 3

in formula mass look at your Periodic Table and find the elements from you compound.

in ex: H20 ----- it has two H and one O

1 element H has 1g x 2 = 2g

1 element o has 16 g x 1 = 16g

add them up = 18g all together

there is 2g of H and 18g of O in one compound of H2O

Just dont over think it man, Im sure you`ll do fine

***The formula mass of a compound or element is the sum of the atomic masses given in the formula of the substance per the Periodic Table (An Introduction to Physical Science, 12th Edition, bu Shippman, Wilson, .and Todd)

Answer 4

Find the mass of each atom within the compound and multiply this by their subscript. Do this for each atom and add them together at the end to get the total mass of the compound.

Example: H2SO4

mass H= 1.01g

mass S= 32g

mass O= 16g

Total mass = 2(H) + S + 4(O) = 98.02g

Answer 5

To determine the formula mass of a compound, you need to calculate the sum of the atomic masses of all the elements present in the compound, taking into account the number of atoms of each element. This information can be found by referring to the periodic table for the atomic masses of each individual element.

Answer 6

By knowing its valency