Why do people use the formula n1V1=n2V2 when performing dilution calculations?

Question

I'm talking about where c=n/V. Where c=concentration in moles/L, n=number of moles, V=volume in litres...

Answer 1

It simplifies the calculation of how much of something to add to a volume of something else to give a concentration of the first something in the second something. Units can be whatever you like - moles, gm/L etc

Answer 2

First of all , I want to say that your formula is incorrect. It should be M1V1 = M2 V2. Let me first explain where this formula comes from.

In the formula, 1 stands for "the initial state" that is before dilution and 2 stands for "the final state" that is after dilution.
Although we talk about the dilution, because your question involves this situation, the same formula can also be used for the solutions to be concentrated by evaporating some of the solvent.

The term " concentration" is to used to express the amount of solvent in a definite amount of a solution. There are various ways of expressing the concentration. The most frequently used one is the "molarity" (M) which gives the number of moles of the solute in 1 liter of the solution;
M = moles of solute / liter of solution
M = n / V

Suppose, you have 400 mL of a solution which contains 2 moles of dissolved table salt. The molarity of the solution will be;
M = 2 mol / 0.4 L = 5 M

If you add 600 mL of water to this solution, only the volume of the solution and consequently the molarity of the solution changes. The number of mole of the solute does not change. We didn't add table salt, we add only water. Since the number of moles of solute does not change during dilution;

Before dilution; n = M1V1
After dilution; n = M2V2

Therefore, the left sides of the two equations will be equal:
M1V1 = M2V2

The difference between V2 - V1 will give you the volume of the solvent to be added to obtained the desired molarity M2.

The same formula can also be used to concentrate the solutions by evaporating the solvent. During evaporation only the some portion of solvent is evaporated, the number of moles of the dissolved solute does not change.

But in this case, V1 > V2 and the difference V1 - V2 will give you the volume of solvent to be evaporated to obtain the desired molarity M2.

Answer 3

N1v1 N2v2 Formula

Answer 4

n is concentration, V is volume, nV is total amount of stuff. This does not change, so

starting amount = final amount

or, in symbols,

n1V1 = n2V2

There is a version of this which you can use for titration problems:

M1V1e1 = M2V2e2

where M is molarity, V volume (again), e number of equivalents (H+ or OH- in acid-base titrations,electrons transferred in oxidation-reduction) per formula unit. For example, e is 1 for HCl but 2 for H2SO4.

Answer 5

pv=k, const,boyle's law
V/ T= k, const,Charles law
n/v=k,Avogadroe's law
combining,PV=nRT,gas eqn
so acc.to Avogadroe's law
n1/v1=k=n2/v2
n1v2=n2v1,if 'n' is the no. of moles
In the case of dilute solns,N1V1=N2V2,where 'N' the normality,
eg,N1=IN,V1=4ml,N2=0.1N,V2=_
N1V1=N2V2
1into 4=0.1 into V2
V2=4/0.1=0.4ml

Answer 6

I'm with you...crazy isn't it.