A solution is made using 200.0 mL of methanol (density 0.7920 g/mL) and 693.1 mL of water (density 1.000 g/mL). What is the mass percent of the methanol

18.6% by mass MtOH

Explanation:

Solution composition = 200ml MtOH + 693.1 ml H₂O

= (200ml MtOH)(0.792g MtOH/ml MtOH) + (693.1 ml H₂O)(1.000g H₂O/ 1 ml  H₂O)

= 158.4 g MtOH + 693.1 g H₂O = 851.5 g

mass% MtOH = (158.4g MtOH/851.5g Solution) x 100% = 18.6% by mass MtOH

the dissolution of polymer can be thermodynamically described in 2 steps.