Solve for the unknown quantity.

(3.0%) (100 mL

V1 = --------------= 10 mL

30.0

10 mL of 30.0 % alcohol must be added to a 100 mL volumetric flask and q.s.

to the mark with water in order to attain a concentration of 3.0 %.

Solution via dimensional analysis:

Calculate the amount of solute in the final (diluted) solution.

1 dL

3.0 mL

100 mL X ------X -------- = 3.0 mL alcohol

100 mL dL

Multiply the amount of solute needed in the final solution times the percent

concentration of the original solution, used appropriately as a factor.

dL

3.0 mL alcohol X -------------- = 0.10 dL

30.0 mL alcohol

Expressing the volume of original solution in milliliters yields the same results

as before.

100 mL

0.10 dL X -------- = 10 mL

dL

A key for this particular type of problem is that in most instances the problem

refers to the preparation of a dilute solution from a concentrated stock.

Another key is in the fact that this type of problem will have either two

concentrations and one volume or two volumes and one concentration.

c. **Example 2**. How much 0.100 Eq/L Ca(OH)2 can be prepared from 10.0 mL

of 6.00 mol/L Ca(OH)2?

Solution. Read the problem carefully and determine the relationship that will

allow you to solve the problem for the unknown quantity.

MD0837

6-7

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