Epinephrine's noob chemistry question

[epinephrine]

Heya,

Decided to make my own thread for my year 11 chemistry questions so any help would be much appreciated!

Anyways first question:

1. 10.0g of NaOH was completely dissolved in water so that the final volume of solution was 200 ml. What is the concentration of         this solution?

[REBORN]

Is it 1.25M?

[ariawuu]

Concentration= n/V, whereby V is in litres
We know the volume (0.2L)
We need to find the moles of NaOH (n)
the equation for the n(NaOH)=m/M, whereby mass is in grams.
Sub in what we know; m= 10g, M= mass number of Na plus mass number of O plus mass number of H,refer to periodic table.

Work what n is then divide by 0.2 will give you your concentration.
Hope that was helpful.

[ariawuu]

Is it 1.25M?

yerp.

[epinephrine]

Haha thank you but why do we use C = n x V  , rather than using concentration = mass of solute / volume ?

[ariawuu]

im assuming its n/v not mass of solute/volume (but you can do that) just depending what the question is asking you to put the concentration in
eg find the concentration(m/v%) of this then you would use mass of solute/volume ^^

whats the answer at the back of your book?

EDIT: that was a good question, but if it's not asking you specifically for m/v% then you would assume its n/v

[tony3272]

Haha thank you but why do we use C = n x V  , rather than using concentration = mass of solute / volume ?

The formula for concentration is c=n/V rather than c=n x V. Using n rather than m is just so that it's units are in

[REBORN]

Haha thank you but why do we use C = n x V  , rather than using concentration = mass of solute / volume ?

it's c = n DIVIDED BY V.

You can find it your way but you'll get it in g/L...the king of concentration is M, molarity, n/L!

EDIT: Beaten.

[Lasercookie]

I think the reason is because n = c x V gives you the answer in Molars (1M = 1 mol/L) which is a nicer unit.

[ariawuu]

I think the reason is because n = c x V gives you the answer in Molars (1M = 1 mol/L) which is a nicer unit.

Haha thank you but why do we use C = n x V  , rather than using concentration = mass of solute / volume ?

it's c = n DIVIDED BY V.

You can find it your way but you'll get it in g/L...the king of concentration is M, molarity, n/L!

EDIT: Beaten.

Haha thank you but why do we use C = n x V  , rather than using concentration = mass of solute / volume ?

The formula for concentration is c=n/V rather than c=n x V. Using n rather than m is just so that it's units are in

probably was a typo....

[epinephrine]

Oh haha whoops my mistake it was a typo its supposed to be n= c x V and yeah it was a multiple choice question which had the answers in (M) so haha silly me I didn't see it 

Haha but thanks anyways guys !

[ariawuu]

yerp M is molarity (mols per litre)= concentration XD

and well done for creating your own chem thread

[epinephrine]

Ok I'm back again

2. calculate the molar concentration present in 1.55L of solution, which contains 1.223g of CaCl₂

Ok so I got 7.11 x 10^-3 but apparently thats wrong?

[REBORN]

I got the same answer...who said it was wrong?

[epinephrine]

Heinemann 1 textbook