Chemistry help needed. Mass percent question?

first... empirical formula = lowest whole number ratios of atoms in the formula.

next, here's the logic we follow to solve the problem

.. (1) assume 100g of the compound

.. (2) convert %'s and and 100g to mass of each element

.. (3) convert masses to moles.. (formulas are in MOLE ratios)

.. (4) simplify the mole ratios to get the empirical formula

here we go

************

steps 1,2,3 combined... (you can do them 1 at a time if you wish)

.. moles H = 100g acid x (1.75g H / 100g acid) x (1 mole H / 1.008g H) = 1.736

.. moles S = 100g acid x (56.14g S / 100g acid) x (1 mole S / 32.06g S) = 1.751

.. moles O = 100g acid x (42.11g O / 100g acid) x (1 mole O / 16.00g O) = 2.632

step 4.. to simplify, we use a trick. We divide all mole values by whichever is the lowest. That forces at least 1 of the numbers to = 1 and the rest to = 1 or be > 1.. (this makes it easier to predict fractions if we need to simplify further). We can do this because we only care about the RATIOS.. not the absolute values. Remember they're based on that 100g we assumed.

so.. the lowest mole value = 1.736 therefore

.. mole H = 1.736 / 1.736 = 1

.. mole S = 1.751 / 1.736 = 1

.. mole O = 2.632 / 1.736 = 1.5 = 3/2

so to get rid of the 3/2 we double everything and get this empirical formula

.. H2S2O3

Treat the percentage compositions as masses so you have 1.75g H 56.14g S and 42.11g O.

Work out how many moles you have of each using the formula

Moles=mass divided by Ar.

Divide each number of moles calculated by the smallest amount to obtain ratio.

Should always be whole numbers so multiply everything in the ratio by 2 if you end up with something like 1.5 for example.