Mole questions (1 Viewer)

[slip]

is n=mv a mole equation,

if so is it moles=mass x volume???

 

[CM_Tutor]

Originally posted by slip
is n=mv a mole equation,

if so is it moles=mass x volume???

It's not an equation I recognise. The ones used in the HSC are:

n = m / M .......... ie moles = mass / molar mass

C = n / V .......... ie concentration = moles / volume

n = N / N_A .......... ie moles = number of formula units / Avogadro constant

n(GAS) = V(GAS) / V_1mol .......... ie moles of gas = volume of gas / volume of 1 mol of gas at the given T, P

 

[slip]

ok thanks

 

[nike33]

n = mv

n = mol.
m = [H+] molarity
v = volume

 

[Xayma]

Molarity usually uses M instead of m (of course Molar Mass can also use M). m normally ='s mass. And that is just a rearragenment of c=n/V since concentration=molarity

 

[CM_Tutor]

And so, for clarity, it is (IMO) better to talk of concentration rather than molarity. (Especially if you are going on to some sort of biologically slanted degree, as you may then deal with molality, and it can be easy to confuse molarity and molality. )

 

[nike33]

ahh i remember reading something with molality in it, is it in the hsc course? also mind explaining what it is?

 

[CM_Tutor]

Nike33: No, molality is not in the HSC course, but since you asked for a definition, here are the ones from General Chemistry by PW Atkins

concentration: See molar concentration.

molality: The number of moles of solute per kilorgam of solvent.

molarity: Molar concentration.

molar concentration: The number of moles of solute per liter of solution.

 

[velox]

what?? My teacher is teaching me al this molarity stuff, so i dont need to know it?

 

[CM_Tutor]

Wrx, molarity, with an 'r' is in the course, molality, with an 'l' is not.

 

[cko]

Originally posted by nike33
n = mv

n = mol.
m = [H+] molarity
v = volume

doesn't [H+] just mean concentration?
so the equation is basically n=cv...?

 

[CM_Tutor]

Originally posted by cko
so the equation is basically n=cv...?

Yes - that's what Xayma was saying in his post.

 

[velox]

oh ic, easy to get confused as said in ur thread

 

[~*HSC 4 life*~]

can somebody explain what this C1V1=C2V2 equation is for? i've only ever used it once in my life and it was never taught to me

 

[CM_Tutor]

It is for dilutions, and dilutions only.

So, for example, to answer questions like:

1. If 25.00 mL of 0.4875 molL^-1 oxalic axid is diluted to 375.0 mL, what will be the new concentration?

2. How much water should I add to 12.3 mL of 1.057 molL^-1 sulfuric acid to make a 0.200 molL^-1 solution?

etc...

 

[Xayma]

If the number of moles in each solution is equal.

Then concentration*volume is the same in each solution.

For example in titrations if they react in a one to one ratio you can speed up the process of finding the unknown by using that formula if you knew the concentration of the standard solution.