a magnesium halide salt has the formula MgX2. A 0.593g sample of MgX2 was dissolved in 100mL of deionized water, followed by the addition of excess NaOH. The precipitate of Mg (OH)2 was filtered, washed, and dried. The precipitate was found to have a mass of 0.187g. what is the percent by mass of Mg in the original unknown compound ?

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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 !