## When to use MiVi=MfVf

Faisal Alshamaa - 1L
Posts: 31
Joined: Fri Apr 06, 2018 11:01 am

### When to use MiVi=MfVf

Hello,
I'm having some difficulty determining when to use the M(initial) x V(initial) = M(final) x V(final) equation in problems. Is there any way to know to use this equation in a type of problem? What kind of problems is it used for?
Thanks!

Sarah Brecher 1I
Posts: 31
Joined: Fri Apr 06, 2018 11:02 am

### Re: When to use MiVi=MfVf

So it depends on what you're given. If you're given 2 different molarities and 1 volume and are asking for the other volume, use this equation. It also works if you're given 2 different volumes and 1 molarity and asked to find the molarity. You would use the equation M= moles/volume when you're only given 2/3 of those values and asked to solve for an unknown.

Bijal Luhar
Posts: 33
Joined: Fri Apr 06, 2018 11:03 am

### Re: When to use MiVi=MfVf

One of the best ways to know when to use an certain equation is to write out was is given in the problem. For example, if they give you a volume and concentration and want you to find the concentration when you have a certain amount of volume. Then it would be safe to assume M1V1=M2V2. Basically just see what you are given and plug in to see if it makes sense!

NabilaNizam-1K
Posts: 30
Joined: Fri Apr 06, 2018 11:04 am

### Re: When to use MiVi=MfVf

Faisal Alshamaa - 1L wrote:Hello,
I'm having some difficulty determining when to use the M(initial) x V(initial) = M(final) x V(final) equation in problems. Is there any way to know to use this equation in a type of problem? What kind of problems is it used for?
Thanks!

You can use this equation to find either molarity/concentration and volume of the solution needed during dilution. Just remember to convert any data given in the question into M and V before plugging them into the equation. The basic idea of this equation is that the number of moles before and after dilution will remain the same.

Harmonie Ahuna-1C
Posts: 30
Joined: Fri Apr 06, 2018 11:01 am

### Re: When to use MiVi=MfVf

Are there some cases where you'll have to use both the M=n/v and MiVi=MfVf equations in a problem?

Chiara Berruto 1K
Posts: 29
Joined: Fri Apr 06, 2018 11:01 am

### Re: When to use MiVi=MfVf

Harmonie Ahuna-1C wrote:Are there some cases where you'll have to use both the M=n/v and MiVi=MfVf equations in a problem?

This wouldn't be likely to happen because the first equation is used to find molarity when given the moles and volume of a solution. If you know the moles of the solution then you wouldn't need to use the second formula because moles of a solution don't change in a dilution.

Anna De Schutter - 1A
Posts: 66
Joined: Wed Feb 21, 2018 3:01 am

### Re: When to use MiVi=MfVf

I'm not too sure that there would exist a case where you would need to use both equations.

However, if for example you are giving n(final) and M(final) as well as M(initial), you could use M=n/V to find V(final) and then the equation M(initial)*V(initial)=M(final)*V(final) to find V(initial).
You could also just write n(final)=M(initial)*V(initial) to find V(initial).

Hope this helps! :)
Anna De Schutter - section 1A

Mjay 1F
Posts: 6
Joined: Fri Apr 06, 2018 11:02 am

### Re: When to use MiVi=MfVf

Was there a problem like this on last week's test? Because some of my friends said that they used it but I still don't know how it would be applied.

Chem_Mod
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Joined: Thu Aug 04, 2011 1:53 pm
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### Re: When to use MiVi=MfVf

The dilution formula is best used when you are diluting a solution having a certain concentration and you want to find out how the concentration of that particular solution has been diluted after increasing the volume of the solution. The final concentration only talks about how the original concentration has been diluted to and does not take factors of other contents (any extra salts or molecules) that are added during a dilution process if there were any.

The TAs will hopefully go over the exam briefly when the exam is returned, if not please ask during office hours if you are still unsure.