Hello, Monica,
Rememer the definition of Molar. Molar means moles/liter. A 1.00M [capital M is generally used to represent Molar. A small m is demeaning to the unit (from the unit himself) , but, more importantly, it be confused with other units such as meter (m).]
As I was starting to say, a 1.00M iron nitrate solution has 1 mole of iron nitrate in 1 liter of solvent, generally water. 10ml of a 1.0M solution would have:
(1.0 moles/liter)*(10 ml)*(0.001 liter/ml) = 0.01 mole
[We needed to covert 10ml to 0,01 liters to be able to cancel the units]
We have 0.01 mole of iron nitrate in 10ml of solution when another 90ml of water is added, bringing the total volume to 100 ml, or 0.100 liter. The new concentration, in Molar, would be:
0.01 mole iron nitrate/0.10 liter.
The final concentration is thus 0.1M iron nitrate.
I just described the basic thinking behind Molarity and dilutions, but there exists a handy relationship when doing simple dilutions. It is
M1V1 = M2V2
M1 and V1 are the initial molarity and volume, while M2 and V2 are the final values. In this case, a simple dilution, we have:
M1V1 - M2V2 and we want to find M2, rearrange:
M2 = (M1V1)/V2
M2 = (1.00M)*(10ml)/(100ml)
M2 = 0.1 M
Since the volume units cancel, we don't need to convert to liters, an added bonus. It is best to understand the basic approach I firsty described, since the simplified equation won't be as useful in more complex problems. Bit M1V1 = M2V2 is easy to remember, and fast when time is important. Keep in mind the basic concept of moles of solute moving from one place to another and you'll be able to confirm that the simpler equation is warranted for a particular problem.
Bob
