Solving Weight/Volume Problems (cont)

b. Example 2. How many milliliters of solution can be prepared from 62.5 mg of

K2SO4 if the desired concentration is 12.5 mg/dL?

Solution. Read the problem carefully and determine what the problem is

asking for.

Total volume of solution expressed in milliliters.

Ratio and proportion is well suited for solving this type of problem.

Set the problem up with respect to the considerations discussed in Appendix A

concerning ratio and proportion.

12.5 mg

62.5 mg

-------- = --------

1 dL

x dL

Solve for the unknown quantity.

(12.5 mg)(x dL) = (62.5 mg)(1 dL)

(62.5 mg)(1 dL)

-------------- = x dL = 5.00 dL

12.5 mg

To completely satisfy the problem, convert deciliters to milliliters.

100 mL

5.00 dL X -------- = 500 mL

1 dL

c. Example 3. What is the prepared by adding 50.0 g CaCO3 to a 250.0 mL

flask and adjusting the volume to the mark?

Solution. Read the problem carefully and determine what the problem is

asking for.

Percent (Solving this type of problem involves expressing the mass of solute

per unit volume.

Since the unit volume is deciliters the first step in problem solving would be to

convert the given volume in milliliters to deciliters.

1 dL

250.0 mL X -------- = 2.50 dL

100 mL

MD0837

2-10