To find the mass of Na+ in sodium sulfate (Na2SO4), we need to consider the molar ratios of Na+ in the compound. In Na2SO4, there are 2 Na+ ions for every 1 Na2SO4 unit. The molar mass of Na2SO4 is 142 g/mol, so in 25 g of Na2SO4, there are about 8.8 g of Na+.