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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: SpottedAng on September 11, 2004, 07:16:10 PM

Title: Finding out the number of electrons in a charge
Post by: SpottedAng on September 11, 2004, 07:16:10 PM

I've been attempting to find out how to do this in my chemistry books for hours and no avail...

If you are given a certain charge of an electron sample, how do you find out how many electrons are in that specific sample?  And after you find the number of electrons, how do you go about finding the mass? Thank you!!

Title: Re:Finding out the number of electrons in a charge
Post by: Demotivator on September 11, 2004, 07:36:23 PM

What do you mean by electron sample? give an example.

Title: Re:Finding out the number of electrons in a charge
Post by: Donaldson Tan on September 12, 2004, 12:16:27 AM

If you are thinking along the line of an anion, eg. Cl^-

1- would means the chlorine atom gains one additional electron. In its neutral charge state, it has 17 electrons already. Hence, the chloride anion would have 18 electrons in total.

Since the mass of an electron is 1/1840 of the mass of a proton, adding an electron hardly changes the atomic mass.

Title: Re:Finding out the number of electrons in a charge
Post by: SpottedAng on September 12, 2004, 01:27:45 PM

All the question says is:

A sample of electrons is found to have a total charger of -5.4475X10^10 C. How many electrons are in this sample?


I still can't find it in the book!!  ???

Title: Re:Finding out the number of electrons in a charge
Post by: Demotivator on September 12, 2004, 01:45:26 PM

Ok
There are 96500 Coulombs of charge per mole of electrons.
5.4475X10^10 C/96500 C/mole = 5.65x10^5 moles of electrons.
One electron has mass of 9.109X10^-31 kg
One mole = 6.022X10^23 electrons
So you can figure the total mass.

Title: Re:Finding out the number of electrons in a charge
Post by: SpottedAng on September 12, 2004, 08:05:03 PM

I'm still confused... I'm not trying to figure out the mass... I need to figure out how many electrons there are..

Thank you for all the help, I just get confused really easy when it comes to calculations.  :-\

Title: Re:Finding out the number of electrons in a charge
Post by: Demotivator on September 12, 2004, 10:39:52 PM

There are 96500 Coulombs of charge per mole of electrons.
5.4475X10^10 C/96500 C/mole = 5.65x10^5 moles of electrons.
Each mole has 6.022X10^23 electrons.
Therefore
number of electrons =  5.65x10^5 moles x 6.022X10^23 electrons/mole = 3.4x10^29 electrons

Title: Re:Finding out the number of electrons in a charge
Post by: Donaldson Tan on September 13, 2004, 12:21:24 AM

Quote from: SpottedAng on September 12, 2004, 01:27:45 PM

A sample of electrons is found to have a total charger of -5.4475X10^10 C. How many electrons are in this sample?

Faraday's Constant, F, corresponds to the total charge of 1 mole of electrons.

F = 96500 Columb Per Mole

No. Of Moles of Electron In The Sample
= Total Charge / Faraday's Constant
= 5.4475X10^10 / 96500

No. of Electrons In The Sample
= No. of Moles X Avagadro's Constant
= (5.4475X10^10 / 96500) X (6.023X10^23)

Title: Re:Finding out the number of electrons in a charge
Post by: ssssss on September 13, 2004, 04:47:41 AM

Quote from: SpottedAng on September 12, 2004, 01:27:45 PM

All the question says is:

A sample of electrons is found to have a total charger of -5.4475X10^10 C. How many electrons are in this sample?


I still can't find it in the book!!  ???

Ok if you want a more simple way.

As you know charge on one electron in 1.6x10^-19c,so 1st calculate the number of electrons by Dividing the number the charge by charge on 1e and then calculate the Moles.1 mole of e = 6.023x10²³ e.

But this will be somewhat more time consuming.