Moles!

[Mallory_Podosin_1H]

I am VERY rusty on the whole concept of moles...and I am finding it difficult to grasp other concepts without fully understanding moles. Does anyone have any advice on what/how to study and review moles? For example - when to use Avogadro's number, what molar mass is for etc. Any good youtube video suggestions or sections of the textbook with the most explanation?

[Sophia_Kiessling_2L]

Bozeman AP chem videos are very helpful!

[janeane Kim4G]

I have almost no chem experience so i might confuse you more lol but I got it down through the equations.
Molar mass of an element is usually measured in g/mol. One mole is the # of atoms in 12g of carbon12, but it’s also Avogadro’s number. (6.02 x10^23). So for example, the molar mass of C on the periodic table is 12.011g/mol. Meaning 6.022 x 10^23 atoms of Carbon weight approx 12.011 grams.
When asked about the amt of moles, you do (mass/molar mass) you will see the grams cancel out, leaving only the moles. For example, in a compound that is 50% C, you would make 50% into 50g out of 100. The molar mass (g/mol) of C is 12.011 so, there would be 4.16 moles of C in the compound.
(50g/12.011g/mol=4.16mol)
You use Avogadros # to find the amount of molecules or formula units in said compound. So, if there are 4.16 moles of C, you would multiply 4.16 by 6.02 x 10^23 to get 2.50 x 10^24 total atoms of C.

TLDR: basically just try to remeber that moles=mass/molar mass, and if 6.02 x 10^23 is involved it usually means they’re looking for the sheer number of atoms.

[deepto_mizan1H]

Definitely check out videos regarding concepts of moles and matter, but I can try to give a short description. A mole is the concept of a certain amount of a compound or element, usually defined by Avogadro's number (6.022*10^23), which tells us about how many particles (atoms, molecules) of whatever we are considering is in one mole of it. This number is derived from the number of atoms in 12g of Carbon-12, which applies to the rest as a standard. The molar mass is defined as the total mass of one mole of such substance, which can be used a nifty conversion factor to find out how much of a compound or element you have. Simply divide your substance amount (in grams) by the molar mass of your substance, and you will be able to find not only how many moles you have, but the number of particles. This also extends to Molarity, (M) the concept of moles of solute divided by volume. TL;DR: Moles are a way for us to conceptualize a standard amount of a substance, to which we can perform further measurements.

[Manya Bali 4E]

Just like 12 inches make up 1 foot, 6.022 x 10^23 (Avogadro’s number) atoms make up one mole of atoms.

Molar mass is the number of grams in one mole of a substance. On the periodic table under carbon, you can see the atomic mass of carbon which is 12.01 atomic units. This relates to moles because every one mole of carbon atoms has a mass of 12.01 grams. This is why molar mass is also represented as grams/mole.

I think this video shows all the steps you would need to solve a chemistry problem using these terms very clearly: https://www.youtube.com/watch?v=MHA7PPX9Glk.

Hope this helps!

[Isabel Bellon 4F]

Same here! I watched Tyler DeWitt's videos on moles and it really cleared it up for me

First video: https://www.youtube.com/watch?v=wI56mHUDJgQ

[Emilee Hosking 1D]

My only previous chem class was my sophomore year so even stoichiometry feels foreign. I had asked few friends who are good at chem about converting grams to moles using stoichiometry, and they have done it a few different ways but got the same answer. Does anyone have any good tips on how to set up a stoichiometry problem that converts grams to moles?

[Mallory_Podosin_1H]

My only previous chem class was my sophomore year so even stoichiometry feels foreign. I had asked few friends who are good at chem about converting grams to moles using stoichiometry, and they have done it a few different ways but got the same answer. Does anyone have any good tips on how to set up a stoichiometry problem that converts grams to moles?

Hi Emilee -
So I did some studying and was able to figure it out! My main trick is to always write down units and it really helps me keep things straight in my head. In converting from grams to moles, you have to use the molar mass which is basically the weight of the molecule. For example CO₂ is C (12.011) + O (15.999) + O (15.999) which equals 44.009. The units are grams/moles.

Using stoichiometry to go from grams to moles:
Start with grams (for example 10g of CO₂)
10g/1 * molar mass with grams on the bottom to cancel with 10g
so:
10g/1 * 1 mol/44.009g = .2mol CO₂

Hope this makes sense! But basically keep track of what units of what molecule you're working with and it will be clearer/easier to understand. Also - I write everything out in fractions and cross out my units as they cancel.