45 pounds of soda ash is dissolved in 155 gal of water to produce a desired concentration. How many pounds of soda ash are needed to make the same desired concentration if exactly 100 gal of water is used?

• A. 69.75
• B. 14.5
• C. 3.4
• D. 29.0

Answer: (D)

Maintaining the same concentration means the soda ash amount scales with the amount of water. The required mass is proportional to the water volume: 45 lb × (100 gal / 155 gal) = 4500/155 ≈ 29.0 lb. So about 29.0 pounds are needed. This assumes concentration is treated as pounds per gallon of water and that solution volume changes are negligible.