Dilution Problems - Chemistry Tutorial - YouTube

hello and welcome to the chemistry solution this tutorial is on dilution

problems when you are diluting a more concentrated solution you're increasing

the volume but the number of moles of solute in the original solution stays

the same so the initial concentration times the initial volume will equal the

final concentration times the final volume sometimes you see this written m1

times v1 equals m2 times v2 and m1 times v1 equals the molarity of the first

solution times its volume which equals m2 times v2 which is the molarity of the

second solution times its volume it's just another way of writing initial and

final and if you look at that given equation initial and if you look at the

first equation initial concentration times the initial volume you know that

if your initial concentration is in moles per liter what's really important

is that your initial and final concentrations or m1 and m2 must have

the same units and your initial and final volumes or v1 and v2 must also

have the same units if you have concentrations in molarity moles per

liter your volume does not necessarily need to be in liters but your initial

volume and your final volume need to have the same units just as your initial

and final concentrations must have the same units if you're asked to solve a

problem where either your volumes have different units or your concentrations

have different units it's going to be necessary to convert one or the other in

order to arrive at concentrations or volumes that have the same units in

order to use this equation let's look at an example how many milliliters of a 2.5

molar NaOH solution are required to make 525 milliliters

of 0.15 molar naoh solution we know that the molarity of something times its

volume will equal the molarity of our other solution times its volume let's

write down the information that we're given our first concentration is 2.5

molar but were asked how many milliliters of that solution are

required so we don't know the first volume the final volume that we want to

arrive at is 525 milliliters with a final concentration of 0.15 zero molar

because our concentrations have the same units of molar we can plug these values

into our equation in order to solve for the volume of our first solution we need

to divide each side by 2.5 molar this allows units of molar to cancel out

and we're left with the volume of our 2.5 molar solution required to be equal

to 0.15 zero times 525 divided by 2.5 and because the units of molar cancelled

out we're left with units of milliliters so the volume of 2.5 molar naoh required

in this problem is 31.5 milliliters let's try another example if 45

milliliters of a six molar HCl solution are diluted to a final volume of 0.25 0

ly ters what is the final concentration again we will use the equation M 1 V 1

equals M 2 V 2 and I think it's helpful to always write down first the

information that you're given the molarity of our first solution is 6

molar and the volume that we have of it is 45 milliliters we're asked what the

concentration would be when we dilute the initial solution to 0.25 0 ly turfs

so our second molarity is unknown and that's the value that we'll be solving

for but if you look at the two volumes given you'll see that one volume is

given a milliliter and one volume is given in litres now it

doesn't matter if we convert volume 1 to liters or if we convert volume 2 to

milliliters but we need to change one of them so that they have the same units

but let's look and see what would happen if we just plugged in our values the way

they were we would set up our problem according to our given equation in order

to solve for m2 we would need to divide by 0.25 liters but what you'll see is on

the left side of your equation milliliters and liters won't cancel out

and we need the volume units on the left hand side to cancel in order to be left

with an appropriate unit of concentration so like I said it doesn't

matter if we change milliliters to liters or liters to milliliters but in

this case I'm going to change volume two which is 0.25 zero liters to milliliters

and I will use my volume and milliliters to plug into our m1 v1 equals m2 v2

equation now when we divide each side by 2.5 times 10 to the second milliliters

units of milliliters will cancel out and we'll be left with a concentration in

molar so in this case the final concentration after we've diluted 45

milliliters of a 6 molar solution to 0.25 zero letters will be one point zero

eight molar thanks for watching the chemistry

solution we hope you enjoyed this tutorial

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