Start with the balanced equation
#M_text(r):color(white)(mmmmll)18.02color(white)(mml)"63.01#
#color(white)(mmm)"3NO"_2 + "H"_2"O" → "2HNO"_3 + "NO"#
Calculate the moles of #"HNO"_3#
#"Moles of HNO"_3 = 57.9 color(red)(cancel(color(black)("g HNO"_3))) × ("1 mol HNO"_3)/(63.01 color(red)(cancel(color(black)("g HNO"_3)))) = "0.9189 mol HNO"_3#
Calculate the moles of #"H"_2"O"#
#"Moles of H"_2"O" = 0.9189 color(red)(cancel(color(black)("mol HNO"_3))) × ("1 mol H"_2"O")/(2 color(red)(cancel(color(black)("mol HNO"_3)))) = "0.4595 mol H"_2"O"#
Calculate the mass of #"H"_2"O"#
#"Mass of H"_2"O" = 0.4595 color(red)(cancel(color(black)("mol H"_2"O"))) × ("18.02 g H"_2"O")/(1 color(red)(cancel(color(black)("mol H"_2"O")))) = "8.28 g H"_2"O"#
