Molarity and Dilution of a Solution

[Brandon Padilla 2L]

How do you figure out problems where you aren't given 3 out of the 4 values? I know how to figure it out when you have at least 3 values from the initial and final moles and initial and final volumes, but sometimes there are problems where only 2 are seemingly given and I don't know how to approach them. Am I missing something?

[Sarah Lesmeister 2F]

you would use the M=n/V formula when you're only given 2 values.

[Elaine Steinberg 3H]

In order to use the equation Minitial[*]Vintial = Mfinal[*]Vfinal, you can only solve for one unknown, not 2.
If you're looking at a specific problem definitely ask!

[Hayley Vu]

It might be that the MinitialVinitial=MfinalVfinal formula is not used to solve your problem. The only other type of problem I can think of is the one where you're given the initial moles of solute, initial volume of water, and an amount of water that is added to that initial amount of water, and you are asked to find the molarity of the final solution. In this case, you would total up the final amount of water and use the M=n/liters to find the molarity of your final solution.

[Jocelynn Franco 1L]

It might be that the MinitialVinitial=MfinalVfinal formula is not used to solve your problem. The only other type of problem I can think of is the one where you're given the initial moles of solute, initial volume of water, and an amount of water that is added to that initial amount of water, and you are asked to find the molarity of the final solution. In this case, you would total up the final amount of water and use the M=n/liters to find the molarity of your final solution.

So then would we use M=n/liters first, then MinitialVinitial=MfinalVfinal?

[Rachel Fox - 3F]

What I usually do in this case is to get as many terms in the equation MinitialVinitial=MfinalVfinal using the information given and often the equation M=n/liters as well. Information such as moles and liters usually is given if the molarity isn't given or something like the moles can be derived from the question (such as if the problem gives you grams and molecular mass instead of moles directly). Then, there are usually enough values at that point to find three of the four variables in the equation, which then makes it easier to solve.

[405566265]

with the given molarity value you can actually get 2 values out of it! you are given the moles of solute over one liter of solution (mol/L) which is molarity (M). You can potentially use that for Vinitial

[Marie Khijniak 2E]

In order to be able to calculate the dilution of a solution, you have to use the equation M(initial)V(initial) = M(final)V(final). To be able to use this equation, you have to be given three out of the four values, since it is impossible to solve for two unknowns in this case. There might be more information given in the problem that may allow you to calculate the second volume or molarity (it may not be given to you directly as a value). If not, then the problem is missing something.