Achemist needs 90 milliliters of a 72% solution but has only 68% and 77% solutions available. find how many milliliters of the 68% solution should be mixed with the 77% solution to get the desired strength.

Mix 50 mL of the 68% solution with 40 mL of the 77% solution to make 90 mL of the 72% solution.

Explanation:

Let the volume required of the 68% solution be mL. The volume of the 68% solution and the 77% solution shall add up to 90 mL. Thus the volume required of the 77% solution shall be mL.

The amount of solute in the 72% solution will be:

.

The mL of the 68% solution will contribute:

.

The mL of the 77% solution will contribute:

.

The two values shall add up to . That is:

.

.

.

In other words, there need to be

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.