Final answer:
To calculate the number of moles of a substance, use its mass and molar mass to find the moles. For MgSO4 in a mixture, the moles of MgSO4 correspond to those of BaSO4 precipitated using stoichiometry. The mass percent of MgSO4 is then derived from the moles of MgSO4 and the total mass of the mixture.Correct answer is option C.
Step-by-step explanation:
To calculate the number of moles of a substance using its mass, one must use the molar mass of the substance. The molar mass is the mass of one mole of a substance and is given in grams per mole (g/mol).
The student is asked to determine the mass percent of MgSO4 in a mixture. Given a precipitate mass of 0.6168 g of BaSO4, we need to relate this to moles of MgSO4 using stoichiometry since MgSO4 reacts with Ba(NO3)2 to form BaSO4. However, without the stoichiometric relationship from the balanced chemical equation, we cannot complete this calculation. Therefore, assuming an equation MgSO4(aq) + Ba(NO3)2(aq) → BaSO4(s) + Mg(NO3)2(aq), each mole of BaSO4 formed indicates the presence of one mole of MgSO4 originally in the mixture.
Using the molar mass of BaSO4 (233.43 g/mol), the moles of BaSO4 in the precipitated sample can be calculated:
Number of moles = mass of BaSO4 / molar mass of BaSO4
Number of moles = 0.6168 g / 233.43 g/mol
Once the number of moles of BaSO4 is found, this equals the number of moles of MgSO4 in the original sample since the ratio is 1:1. Then, the mass percent of MgSO4 can be determined using the total mass of the sample (0.4550 g).