Question

2. (Exercise 4.1.6) A liquid adhesive consists of a polymer dissolved in a solvent. The amount of polymer in the solution is important to the application. An adhesive dealer receives an order for 3000 lb of an adhesive solution containing 13% polymer by weight. On hand are 500 lb of 10% solution and very large quantities of 20% solution and pure solvent. Calculate the weight of each that must be blended together to fill this order. Use all of the 10% solution.

Answer 1

Answer:

800 lb of pure solvent , 1700 lb of 20% solution and 500 lb of 10% solution will be mixed to form 3000 lb of 13 % solution .

Explanation:

3000 lb of 13% solution is required .

Total adhesive in weight = 3000 x .13 = 390 lb of adhesive

Available = 500 lb of 10% solution = 50 lb of adhesive

Rest = 390 - 50 = 340 lb required .

rest mass of solution = 3000 - 500 = 2500 lb

mass of adhesive required = 340 lb

Let the mass  of 20% required be V

mass of adhesive = .20 V

.20 V = 340

V = 1700

rest of the volume = 2500 - 1700 = 800 lb which will be of pure solvent

So 800 lb of pure solvent , 1700 lb of 20% solution and 500 lb of 10% solution will be mixed to form 3000 lb of 13 % solution .

Answer 2

To form 3000 lb of 13 % solution we need 800 lb of pure solvent, 1700 lb of 20% solution, and 500 lb of 10% solution.

Required wieghts of each solution:

The required solution is 3000 lb of 13% solution

Total adhesive = 3000 x 0.13 = 390 lb

Available adhesive = 500 lb of 10% solution = 50 lb

The required adhesive  = 390 - 50 = 340 lb

The rest mass of solution is = 3000 - 500 = 2500 lb

If we assume the weight of 20% solution required to be W, then:

mass of adhesive = 0.20 W

0.20 W = 340

W = 1700 lb of 20% solution

Remaining volume = 2500 - 1700 = 800 lb

So, the pure solvent has a weight of 800 lb.

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