The concentration of SO42– ions in a 60.0 mL sample of seawater is determined by adding a solution of BaCl2 and precipitating the SO42– as BaSO4. After the precipitate is filtered from the solution, it is dried and weighed. If the mass of BaSO4 recovered is 0.448 g, what is the sulfate concentration of the seawater sample? Express your answer in mmol/L.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !