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### Topic: Calculating number of ions  (Read 22960 times)

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#### steph_r

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##### Calculating number of ions
« on: July 25, 2008, 09:18:49 AM »
Hi there!
Just wondering whether i could have some assistance with this quesiton.

Calculate the number of ions present altogether in 25.0mL (0.025L) of 0.050M aluminium chloride (AlCl3)

I worked out the following:
The amount (in mol) of aluminium chloride: 1.3 x 10^ -3
The amount (in mol) of aluminium ions: (1.3 x 10^ -3) x 1 = 1.3 x 10^-3
The amount (in mol) of chloride ions: (1.3 x 10^ -3) x 3 = 3.9 x 10^ -3

I just don't know how to go about answering the question above.
Help would be greatly appreciated. Thanks

#### Astrokel

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##### Re: Calculating number of ions
« Reply #1 on: July 25, 2008, 09:25:56 AM »
hey steph_r

you are right and one more step to the answer and that is to covert to no. of ions for each species and sum them up

good luck
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#### steph_r

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##### Re: Calculating number of ions
« Reply #2 on: July 25, 2008, 09:35:15 AM »
Would i be able to have some assistance with that? That is, converting to no. of ions? I'll be able to add them up..

Im just a little bit confused..

Thank you for your help and patience, Astrokel

#### Astrokel

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##### Re: Calculating number of ions
« Reply #3 on: July 25, 2008, 09:44:55 AM »
hey,

No. of particles or ions = no of moles x Avogadro's constant

Avogadro's constant = 6.02 x 10^23
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#### steph_r

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##### Re: Calculating number of ions
« Reply #4 on: July 25, 2008, 09:50:06 AM »
Yes.. ive come across that formula, but ive always said: number of particles, instead of number of ions. I think thats why i got a little confused.. but not your fault

So, do i use N = n/Na for both:
The amount (in mol) of aluminium ions: 1.3 x 10^-3, and
The amount (in mol) of chloride ions:  3.9 x 10^ -3

and then add them together? Is that what you mean?

Thank you once again

#### Astrokel

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##### Re: Calculating number of ions
« Reply #5 on: July 25, 2008, 09:56:18 AM »
hey,

yes, but N=n/Na? sorry but i don't understand your notation for the formula. No of particles in general means ions, molecules, atoms...
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#### steph_r

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##### Re: Calculating number of ions
« Reply #6 on: July 25, 2008, 09:59:19 AM »
Sorry,
At school we use:
N = n / NA, meaning :

no. of particles = no. of mole / Avogadro's constant

#### Astrokel

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##### Re: Calculating number of ions
« Reply #7 on: July 25, 2008, 10:04:17 AM »
hey

The formula is wrong, should be

hey,

No. of particles or ions = no of moles x Avogadro's constant

Avogadro's constant = 6.02 x 10^23
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### steph_r

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##### Re: Calculating number of ions
« Reply #8 on: July 25, 2008, 10:06:43 AM »
Thank you, Astrokel! I can't believe it was just a silly mistake..

Thank you for your help.. i really appreciate it!!

#### P

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##### Re: Calculating number of ions
« Reply #9 on: July 25, 2008, 10:12:10 AM »

At school we use:
N = n / NA, meaning :
no. of particles = no. of mole / Avogadro's constant

It is right if you take:

n = number of particles/molecules/ions
N = No. of moles
NA = Avagadro's number

I think you just mixed up the definitions of N and n.

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#### steph_r

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##### Re: Calculating number of ions
« Reply #10 on: July 26, 2008, 03:46:44 AM »

At school we use:
N = n / NA, meaning :
no. of particles = no. of mole / Avogadro's constant

It is right if you take:

n = number of particles/molecules/ions
N = No. of moles
NA = Avagadro's number

I think you just mixed up the definitions of N and n.

Yes, i think i did mix them up. At least now i won't forget.  Thank you!

#### Mitch

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##### Re: Calculating number of ions
« Reply #11 on: July 27, 2008, 05:29:40 AM »
Remember Avogadro's number is easiest to remember in units of inverse mols (mol-1) at this level of chemistry.
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#### calcium

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##### Re: Calculating number of ions
« Reply #12 on: July 28, 2008, 08:54:49 AM »
Remember Avogadro's number is easiest to remember in units of inverse mols (mol-1) at this level of chemistry.

can u expand on that idea please

#### Astrokel

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##### Re: Calculating number of ions
« Reply #13 on: July 28, 2008, 09:16:20 AM »
hey!

What Mitch is saying is that Avogadro's constant actually mean there are approximately 6.02 x 10^23 particles PER MOLE. Therefore the unit is in inverse mole.
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!