Final answer:
To find the percentages of aluminum and magnesium in the alloy through gravimetric analysis, the mass of Al in Al₂O₃ and Mg in MgO must be calculated using their molecular weights based on the mass of the precipitate and ignited mixture. Unfortunately, without the molar masses or stoichiometric details, a numerical answer cannot be provided.
Step-by-step explanation:
To calculate the percentage by weight (% w/w) of aluminum (Al) and magnesium (Mg) in the alloy, we will perform gravimetric analysis based on the data provided. We begin with a 0.611 g sample of an alloy which after being dissolved and treated to prevent interferences, is treated with 8-hydroxyquinoline to produce a mixed precipitate of Al(C₉H₆NO)₃ and Mg(C₉H₆NO)₂ weighing 7.815 g. Upon ignition, this converts to Al₂O₃ and MgO, which weighs 1.002 g.
The masses of pure Al and Mg in the precipitate are equivalent to the masses of Al₂O₃ and MgO in the ignited sample. To find the percentage of Al in the alloy, we calculate the mass of Al in Al₂O₃ using its molecular weight, and then we determine the mass percentage of Al in the original sample. Similarly, to find the percentage of Mg, we calculate the mass of Mg in MgO using its molecular weight, and subsequently calculate its mass percentage in the original sample. The sum of the percentages of Al and Mg should be 100% as they are the only two metals present in the alloy. It is important to account for stoichiometry in the conversion from Al(C₉H₆NO)₃ and Mg(C₉H₆NO)₂ to Al₂O₃ and MgO.
Unfortunately, without the molar masses or additional information on the stoichiometry of the reactions, we are unable to provide a numerical answer for the percentages. In practical applications, these values would be determined by using the known molar masses of the compounds involved in the reaction.