设浓硫酸的体积为x,500mL=500cm3x?1.84g∕cm3×98%=500cm3×1.14g/cm3×20%x=63.2cm3=63.2mL加水的体积为:(500cm3×1.14g/cm3-63.2cm3×1.84g/cm3)÷1g/cm3=453.7cm3=453.7mL答:需要63.2mL浓硫酸,需要加水453.7mL.