Posted by Jason on .
You mix 19.5 gallons of a mixture containing 12 wt% NaCl (sol'n density = 1.0837 g/cm^3) with V2gallon sol'n that is 20 wt% NaCl (sol'n density = 1.1453 g/cm^3). Needed mixture is 19 wt% NaCl
Whats the V2 in gallons?
(all solutions are in water so just dealing with NaCl)

Chemistry 
Gaurav,
V1 =19.5gellon=2113.2cm^3
TM1 =2113.2*1.0837= 22900.9 g
M1= 12*TM1= 2748.1 g
V2 =?
TM2 =V2*1.1453
M2 = 20*V2*1.1453
V3=V1+V2 (mixing of two solutions)
Conservation of mass:
M3=M1+M2,
M3= 12*V1*1.0837 + 20*V2*1.1453 ....I
TM3 = TM1+TM2,
M3 = 19*TM3
= 19*(V1*1.0837 + V2*1.1453) ......II
equate equation I and II
(you have value of V1, so its just 1 variable equation)
V2= 129.158 gellons Ans