Why is it desirable to know the exact concentration of solutions rather than whether the are concentrated or dilute?

Answer 1

Because it's not open to interpretation.

If I ask you for a "long stick" and you come back with something 4' long and I look at you like you're an idiot and say "I said a long stick" because I had something in the 10' range in mind, then that was a waste of your time, right? And you have every right to be miffed at me for not being specific enough the first time.

However, if I ask you for a stick at least 8' long and you come back with that 4' long stick, then I have every right to look at you like you're an idiot and be miffed at you for ignoring very clear instructions.

As it turns out, "concentrated" and "dilute" do have specific implied meanings in chemistry; "concentrated" means "exactly as it came out of the stock bottle" and "dilute" is frequently assumed to be 6 M (which isn't all that dilute; for a lot of common acids, for example, it represents between a 1:1 and 1:2 mixture of the stock solution with water) . However, unless you're a chemist yourself, you may not know this, and assume that you don't need to worry too much about spilling "dilute" sulfuric acid on yourself, when in fact it's a cause for serious concern.

Answer 2

Because if you are dealing with a specific chemical compound you may be talking about a substance which changes properties and effectiveness based on even small variations in concentration.

If you have no idea the degree of concentration than you have no idea of the effectiveness the mixture is going to have.

The difference in even 1 part per million can be the difference between life and death with toxic chemicals that need to be closely regulated.

Or even lets just talk about cooking where life and death are not at stake, the difference in diluting a volume of salt in water is the difference between a delicious tasting piece of food and attempting to drink salt water.

Just because you diluted the salt with water, doesn't make it taste good, but knowing that you concentrated it to an exacting standard which is known to be safe for eating may produce something delicious.

The bigger question is why wouldn't you want to know the exact concentration of a solution? It's not safe to guess and the results may be inedible.

Answer 3

Knowing the molarity is more meaningful because by knowing it you can not only know if it is diluted or concentrated, but also the actual concentration.