### Avogadro's Number?

Posted:

**Thu Oct 03, 2019 1:08 pm**I know avogadros number is 6.022 x 10^-23, and it is a constant. I'm just unsure when I should be using it in an equation because most problems do not tell you when to use it.

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=26&t=46074

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Posted: **Thu Oct 03, 2019 1:08 pm**

I know avogadros number is 6.022 x 10^-23, and it is a constant. I'm just unsure when I should be using it in an equation because most problems do not tell you when to use it.

Posted: **Thu Oct 03, 2019 1:13 pm**

Avogadro's number is 6.022*10^23 (not -23). You use the number when converting moles to molecules/atoms.

Posted: **Thu Oct 03, 2019 1:21 pm**

Think of Avogadro's Number as having the units atoms (or molecules or formula units) per mol for when you're doing dimensional analysis.

Posted: **Thu Oct 03, 2019 1:24 pm**

Avogadro's number should be used if a problem asks for formula units, atoms, or molecules. To convert something to molecules or formula units, multiple moles by Avogadro's number. An example of this would be problem E.9 parts a and b.

Posted: **Thu Oct 03, 2019 1:48 pm**

When you are asked to convert to formula units, atoms, or molecules, use avogadro's number.

Posted: **Thu Oct 03, 2019 2:10 pm**

It's important to know Avogadro's number because it's equivalent to the number of atoms in a single carbon 12, and normalized as a way to measure a single mole.

Whenever we need Avogadro's number, I think it will be given to us, but most regularly you'll need to use it in order to convert from moles to number of atoms.

Whenever we need Avogadro's number, I think it will be given to us, but most regularly you'll need to use it in order to convert from moles to number of atoms.

Posted: **Thu Oct 03, 2019 4:14 pm**

As the previous answers mentioned, it's just a specific name for the number 6.022 x 10^23. Generally you would just think of it as a mole.

Posted: **Thu Oct 03, 2019 4:21 pm**

Avogadro's Number is used to convert from moles to actually number of atoms and vise versa. If a problem asks for specifically the number of atoms (not in moles), then you will need to multiply the moles by Avogadro's number. If you need to convert from actual number of atoms to moles then simply divide the number by Avogadro number.

Posted: **Thu Oct 03, 2019 9:50 pm**

How do you know when to multiply using Avogadro's number and when to divide?

Posted: **Thu Oct 03, 2019 9:53 pm**

Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number.

Posted: **Thu Oct 03, 2019 10:37 pm**

PriscillaLi_3G wrote:How do you know when to multiply using Avogadro's number and when to divide?

Generally, you use Avogadro's number (6.022 X 10^23 atoms/mol) when you are trying to do a mole-to-molecules/atoms/formula units conversion. When solving a problem, it always helps me to write out the units to see where the units can cancel out. For example, if I have the molar mass of oxygen (16.00 g/mol) and I want to figure out how many atoms are in this, I would divide by Avogadro's number because the unit, mol, would cancel out this way.

Posted: **Thu Oct 03, 2019 10:40 pm**

IreneGi4C wrote:Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number.

I'm not that sure if we will need to know it for this class, but I heard that Lavelle does give constants on exams, but I'm still not 100% sure. From my experience in high school, Avogadro's number was something we were expected to memorize though.

Posted: **Thu Oct 03, 2019 10:41 pm**

IreneGi4C wrote:Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number.

I don't know if we'll be given the number but honestly we use Avogadro's number often enough in calculations that it'll become second nature to you after just doing a few problems.

Posted: **Thu Oct 03, 2019 11:23 pm**

IreneGi4C wrote:Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number.

I don't think we need to memorize the number for the test, I think Lavelle mentioned having a front sheet on tests with the constants and equations.

Posted: **Thu Oct 03, 2019 11:44 pm**

If you are not sure when to use Avogadro's number I recommend solving E17. The number will be used in part c of the question and could potentially give you a better understanding. Hope this helps!

Posted: **Thu Oct 03, 2019 11:47 pm**

Avogadros number is a constant, 6.022 x 10^23. It describes the number of atoms, molecules, or "things" in a mole. Typically you use this constant when the question asks you to find the number of molecules OR atoms in a mol.

Take the number of mols derived from the problem and use dimensional analysis and multiply by avigardros number over(divided by) mols

Take the number of mols derived from the problem and use dimensional analysis and multiply by avigardros number over(divided by) mols

Posted: **Thu Oct 03, 2019 11:53 pm**

Avogadro's number is 6.022*10^23 and it can be used to convert moles to atoms