You want to purify 10.0 g of benzoic acid that has been contaminated with 0.2 g of salicylic acid According to the Merck Index, water solubilities of the two compounds are as follows:

Benzoic acid H20 Solubility (g/10 mL) Salicylic acid H20 Solubility (g/10 ml) Temperature (°C)
0.029 0.020 20
0.221 80
0.680 95

a. What volume of boiling water (mL) is needed to dissolve the 10.0 g of benzoic acid?
b. When the water is cooled back to room temperature what percentage of the original benzoic acid and salicylic acid remain in solution?

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 !