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### formula units

Posted: Sun May 06, 2018 7:52 pm
I was looking back at the fundamentals and I kept seeing the phrase "formula units." When a question asks you to find a quantity in terms of formula units does that just mean in terms of atoms?

### Re: formula units

Posted: Sun May 06, 2018 8:27 pm
Yes, you can use Avogadro's number to convert to formula units.

### Re: formula units

Posted: Sun May 06, 2018 8:37 pm
Yeah I had the same question but I think it just means number of atoms.

### Re: formula units

Posted: Sun May 06, 2018 9:39 pm
I had this question too, I don't think it will be unclear like this on the test.

### Re: formula units

Posted: Tue Oct 02, 2018 11:14 am
Hello hello! I just had a quick question regarding formula units. What is the difference between number of atoms and formula units? For section E's homework 9b, the number of atoms and formula units came out to be different answers.

### Re: formula units

Posted: Tue Oct 02, 2018 11:23 am
The way I understand it is:
formula units can mean atoms or molecules, depending on what the question is asking for. For example, if you need to find the number of formula units in a a certain mass of H2O, you calculate the number of H2O molecules. But if it asks you to find the number of hydrogen atoms in a certain mass of H2O, then you calculate the number of H atoms.

### Re: formula units  [ENDORSED]

Posted: Tue Oct 02, 2018 11:24 am
See my answers here:

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=26&t=32772&p=105307&sid=eed5351ba46c7edaa654177d564c3d71&sid=7e485d68778fbf5e6e0db05b8d384ba2#p105307

Formula units apply to salts. Incorrect to refer to NaCl as a molecule or molecular formula.
NaCl is a salt and its formula is referred to as a formula unit.
In this formula unit there are two atoms.

For the salt MgCl2 its formula unit has 3 atoms.

And also read this post:

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=156&t=32737&sid=7e485d68778fbf5e6e0db05b8d384ba2

### Re: formula units

Posted: Tue Oct 02, 2018 10:40 pm
Yes I think I have the same problem. Thanks for answers above!

### Re: formula units

Posted: Wed Oct 03, 2018 7:08 pm
I was unsure about what the problems meant by formula units as well, but I just treated it as sort of a synonym for "molecule". So one of the problems asked how many formula units of a compound are in 5.15 g, I just found how many molecules would be in 5.15 g, using Avogadro's number.

### Re: formula units

Posted: Wed Oct 03, 2018 9:48 pm
Formula units is the equivalent of molecules for different compounds.

Molecules are for molecular compounds. Formula units are for atomic compounds.

### Re: formula units

Posted: Wed Oct 03, 2018 11:45 pm
Moles are just a measurement kind of like a dozen. You can define what the moles, or dozen, is of so it could be atoms, molecules, formula units, or donuts. The number is the same regardless of what thing its describing.

### Re: formula units

Posted: Wed Oct 03, 2018 11:47 pm
Does anybody know what unit "pm" is? I'm doing the homework right now and I'm not sure what it stands for.

### Re: formula units

Posted: Thu Oct 04, 2018 12:15 am
I think the "pm" you're referring to is the measurement unit of a picometer, which is 10^-12! So to convert that to the unit of a meter which most questions have been using, you would multiply your answer by 10^12.

### Rounding Up

Posted: Thu Oct 04, 2018 6:16 pm
Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is?

### Re: formula units

Posted: Thu Oct 04, 2018 6:22 pm
I believe we dont need to round up the atomic masses in the periodic table, the reason being it would make our calculated answers for problems slightly less accurate than the real answers

### Re: formula units

Posted: Thu Oct 04, 2018 7:47 pm
Thank you!

### Re: formula units

Posted: Thu Oct 04, 2018 8:39 pm
My TA said to not round the atomic masses given on the periodic table, just use them as is. One of the few times that it's safe to round, is when you are trying to find the empirical formula for a compound because that's when you really want the whole numbers.

### Re: Rounding Up

Posted: Thu Oct 04, 2018 10:19 pm
Thank you for the feedback!

### Re: formula units

Posted: Thu Oct 04, 2018 10:21 pm
What was the unit of measurement only used by chemists, also known as 10 to the -10 power?

### Solution Concentration

Posted: Thu Oct 04, 2018 10:33 pm
How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out?

### Re: formula units

Posted: Thu Oct 04, 2018 11:27 pm
I believe the unit you are thinking of is the Ãngström, 1Ã = 10^(-10).

### Re: formula units

Posted: Fri Oct 05, 2018 2:00 am
From what I understand, "formula units" can be somewhat interchangeable with molecules. For example, how many formula units of H20 are in 2g of water?
the answer would be 6.7x10^22 formula units

### Re: formula units

Posted: Fri Oct 05, 2018 2:17 am
Sophia Ding 1D wrote:I think the "pm" you're referring to is the measurement unit of a picometer, which is 10^-12! So to convert that to the unit of a meter which most questions have been using, you would multiply your answer by 10^12.

You're right the picometer is 10^-12 and you would multiply by 10^12 to get meters but the question that is being referred to just asks for length meaning the conversion is arbitrary.

### Re: formula units

Posted: Fri Oct 05, 2018 2:20 am
Danny Elias Dis 1E wrote:What was the unit of measurement only used by chemists, also known as 10 to the -10 power?

The unit that is 10^-10 is the Angstrom which has the symbol Å.

### Re: Rounding Up

Posted: Fri Oct 05, 2018 7:12 am
Simran Athwal-Dis 3A wrote:Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is?

We can calculate everything with the atomic masses given on the periodic table, and then we can round after we consider significant figures at the end of the problem! This will allow us to have more accurate results. :)

### Re: formula units

Posted: Fri Oct 05, 2018 9:47 am
The "formula units" phrasing throws me off a bit for a question where I am trying to find the "formula units of compound" in a certain amount of grams. Do I just set it up as conversion from grams to moles using molecular weight and solve for the moles of the compound as a whole?

### Re: formula units

Posted: Fri Oct 05, 2018 9:58 am
I'm also confused about formula units. Are they synonymous with "parts" within a salt? Why and when would a chemist use the word formula unit in place of the word atom?

Chem_Mod wrote:See my answers here:

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=26&t=32772&p=105307&sid=7e485d68778fbf5e6e0db05b8d384ba2&sid=7be8fc103320c58b2eb3a9da4183dc33#p105307

Formula units apply to salts. Incorrect to refer to NaCl as a molecule or molecular formula.
NaCl is a salt and its formula is referred to as a formula unit.
In this formula unit there are two atoms.

For the salt MgCl2 its formula unit has 3 atoms.

And also read this post:

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=156&t=32737&sid=7be8fc103320c58b2eb3a9da4183dc33

### Re: formula units

Posted: Fri Oct 05, 2018 5:20 pm
Are salts the only compounds for which you use Formula Units as opposed to Molecule? Or is any compound with 2 different elements a Formula Unit?

### Re: formula units

Posted: Fri Oct 05, 2018 5:23 pm
Any ionic or covalent solid compound not just salts

### Re: Rounding Up

Posted: Fri Oct 05, 2018 5:27 pm
Simran Athwal-Dis 3A wrote:Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is?

I would leave them as is and you can round using significant figures at the end of the problem

### Re: Solution Concentration

Posted: Fri Oct 05, 2018 6:51 pm
Simran Athwal-Dis 3A wrote:How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out?

These things are stated in the problem, whether it is explicit or implicit. It helps to identify what the numbers mean in the given problem, and record them accordingly as you read. There should only be one of these answers missing, in which you would manipulate the equation M[initial]*V[initial]=M[final]]*V[final].

For example:

What volume of 0.0368 M of KMnO4 is needed to prepare 250ml of 1.50*10^-3 M of KMnO4?

From this we know that we are trying to find a volume of KMnO4. Note that the initial molarity is explicitly stated: 0.0368 M of KMnO4. The final volume we are trying to get is 250ml, which is also explicitly stated. The final molarity is given as 1.50*10^-3 M KMnO4. The missing value is the initial volume. Manipulate the previouslt stated equation to solve for V[initial]. Don't forget to convert mL to L, as Molairty is measured in Liters.

I hope this helps.

### Re: formula units

Posted: Fri Oct 05, 2018 7:05 pm
I have a simple question regarding basic chemistry:

How can you determine the reactants in a chemical reaction based off of the products?

### Re: formula units

Posted: Fri Oct 05, 2018 11:22 pm
So is the term 'formula units' only relevant when talking about compounds?

### Re: formula units

Posted: Sat Oct 06, 2018 3:26 pm
Wait, so when it is talking about formula units, it does not specifically mean atoms/molecules, right?

### Re: formula units

Posted: Sat Oct 06, 2018 3:58 pm
Formula units and molecules are pretty much the same, except formula units refer to ionic compounds (e.g.NaCl), and molecules refer to molecular compounds.
NaCl is the formula unit for table salt.
One cannot refer to NaCl as a molecular formula because NaCl is not a molecule.

### Re: formula units

Posted: Sun Oct 07, 2018 6:13 pm
Yes I think you just use Avogadro's number to find the number of atoms or molecules!

### Re: formula units

Posted: Sun Oct 07, 2018 7:44 pm
This thread is similar to a question I jsut asked. I'm just confused on when to use formula units and when to use other names, like ions, atoms, or molecules? Thanks!

### Re: formula units

Posted: Sun Oct 07, 2018 11:32 pm
I believe a formula unit is the empirical formula incase that makes it easier to understand

### Re: formula units

Posted: Mon Oct 08, 2018 10:18 am
Here's a pretty helpful flowchart I drew the other day to use whenever you try converting from a particular unit to another unit!

In order to get formula units from moles you would multiply by Avogadro's number (6.022 x 10^23) by the number of moles that you have.

Hope this helps.

### Re: formula units

Posted: Thu Oct 11, 2018 9:49 pm
You can use Avogadro's number for atoms, molecules, or formula units.
Formula Units apply to ionic compounds, molecules apply to molecular compounds, and you calculate atoms when in reference to elements.

Posted: Thu Oct 11, 2018 11:10 pm
Hi, I had a quick question. How do we check how many times we posted on Chemistry Community? Do we go on our profile?

### Re: Solution Concentration

Posted: Thu Oct 11, 2018 11:14 pm
Andreana Vetus 1A wrote:
Simran Athwal-Dis 3A wrote:How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out?

These things are stated in the problem, whether it is explicit or implicit. It helps to identify what the numbers mean in the given problem, and record them accordingly as you read. There should only be one of these answers missing, in which you would manipulate the equation M[initial]*V[initial]=M[final]]*V[final].

For example:

What volume of 0.0368 M of KMnO4 is needed to prepare 250ml of 1.50*10^-3 M of KMnO4?

From this we know that we are trying to find a volume of KMnO4. Note that the initial molarity is explicitly stated: 0.0368 M of KMnO4. The final volume we are trying to get is 250ml, which is also explicitly stated. The final molarity is given as 1.50*10^-3 M KMnO4. The missing value is the initial volume. Manipulate the previouslt stated equation to solve for V[initial]. Don't forget to convert mL to L, as Molairty is measured in Liters.

I hope this helps.

Thank you so much. It did help with the example you gave!

### Re: Rounding Up

Posted: Thu Oct 11, 2018 11:16 pm
Daniel Bowen 3I wrote:
Simran Athwal-Dis 3A wrote:Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is?

I would leave them as is and you can round using significant figures at the end of the problem

Thank You!

### Re: Rounding Up

Posted: Thu Oct 11, 2018 11:17 pm
Sapna Ramappa 3G wrote:We can calculate everything with the atomic masses given on the periodic table, and then we can round after we consider significant figures at the end of the problem! This will allow us to have more accurate results. :)

Thank you so much!

### Re: Solution Concentration

Posted: Thu Oct 11, 2018 11:19 pm
Simran Athwal-Dis 3A wrote:How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out?

I think most of the questions will state them if not, you can look for hints in the question. For example, if the question is adding water to dilute the molarity, you will know the higher molarity is the initial molarity because dilution means to decrease the molarity.

### Re:

Posted: Fri Oct 12, 2018 12:10 am
Simran Athwal-Dis 3A wrote:Hi, I had a quick question. How do we check how many times we posted on Chemistry Community? Do we go on our profile?

I think theres an option in profile which shows your posts!

### Re: formula units

Posted: Fri Oct 12, 2018 8:23 pm
I looked at formula units as the number of atoms/molecules, depending on what is given. I used Avogadro's number to find the formula units asked for in the problem.

### Re: formula units

Posted: Sat Oct 13, 2018 3:01 pm
Ismail 1F wrote:Yes, you can use Avogadro's number to convert to formula units.

so that will be the only number we use if it says that?

### Re: Re:

Posted: Sat Oct 13, 2018 10:44 pm
lukezhang wrote:I think theres an option in profile which shows your posts!

Thank You!

### Re: Solution Concentration

Posted: Sat Oct 13, 2018 10:47 pm
Andreana Vetus 1A wrote:These things are stated in the problem, whether it is explicit or implicit. It helps to identify what the numbers mean in the given problem, and record them accordingly as you read. There should only be one of these answers missing, in which you would manipulate the equation M[initial]*V[initial]=M[final]]*V[final].

For example:

What volume of 0.0368 M of KMnO4 is needed to prepare 250ml of 1.50*10^-3 M of KMnO4?

From this we know that we are trying to find a volume of KMnO4. Note that the initial molarity is explicitly stated: 0.0368 M of KMnO4. The final volume we are trying to get is 250ml, which is also explicitly stated. The final molarity is given as 1.50*10^-3 M KMnO4. The missing value is the initial volume. Manipulate the previouslt stated equation to solve for V[initial]. Don't forget to convert mL to L, as Molairty is measured in Liters.

I hope this helps.

Yes, this did indeed help me, especially when you gave the example.

### Re: formula units

Posted: Sat Oct 13, 2018 11:01 pm
Hello!
May someone explain more how e- structure give rise to light?

Also, during my lecture I had on Oct. 10th, Dr. Lavelle went over an example using the formula:
Wavelength= hc/E
He included the following:
(6.626 * 10^-34 Js)(3.00 * 10^8 m/s)/3.61 *10^19 J)
Where did he get his numerator is what I am asking?

### Re: formula units

Posted: Sun Oct 14, 2018 8:05 pm
The numbers on the numerator are constants which will always be given and they are found on the "constants and Equations" worksheet.

### Re: formula units

Posted: Tue Oct 16, 2018 2:34 pm
Formula Units are the same thing as molecules except for compounds with ionic bonds.

### Re: formula units

Posted: Tue Oct 16, 2018 3:37 pm
Thanks!

### Re: formula units

Posted: Tue Oct 16, 2018 6:56 pm
Yes, it just means number of atoms which means you use 6.022x10^23

### Re: formula units

Posted: Thu Oct 18, 2018 12:00 am
Yes, which is the Avogadro Number.

### Re: Solution Concentration

Posted: Fri Oct 19, 2018 1:55 pm
Simran Athwal-Dis 3A wrote:How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out?

In a problem that involves M1V1=M2V2 you must first identify which you are trying to solve for. If you are solving for final molarity, you know that the molarity the problem gives is the initial molarity. Of the two volumes, the one that comes first is usually the initial volume. If it does not state explicitly what the final volume is, you usually add the amount of water "added" to the solution to the initial volume to get the final volume.

### Re: Solution Concentration

Posted: Wed Oct 24, 2018 4:03 pm
AriaSoeprono4I wrote:[quote=In a problem that involves M1V1=M2V2 you must first identify which you are trying to solve for. If you are solving for final molarity, you know that the molarity the problem gives is the initial molarity. Of the two volumes, the one that comes first is usually the initial volume. If it does not state explicitly what the final volume is, you usually add the amount of water "added" to the solution to the initial volume to get the final volume.

Thank you so much!

### Re: formula units

Posted: Sun Oct 28, 2018 8:35 pm
I was confused about this as well. Thank you so much for the clarification! Does anyone know in what depth we need to know these bonds for the test? (just in terms of specific elements or molecules or even just sketching them out)

### Quantum #s?

Posted: Mon Oct 29, 2018 10:20 pm
Hello, I had a quick question. One of the quantum numbers, the one where you have to determine if it is +1/2 or -1/2. How do you figure out if it is +1/2 or -1/2 from only the periodic table? I know how to find the n, l, and ml, but not that specific one. May anyone help to explain?

### Re: formula units

Posted: Thu Nov 08, 2018 3:38 pm
For the midterm, does anyone knows how much the units are worth when graded?

### Re: formula units

Posted: Thu Nov 08, 2018 5:09 pm
Arlene Linares 3A wrote:For the midterm, does anyone knows how much the units are worth when graded?

I believe both units and sig figs are each worth one point.

### Re: formula units

Posted: Sat Nov 10, 2018 7:10 pm
Thanks

### Re: formula units

Posted: Sat Nov 10, 2018 7:10 pm
Thanks

### Re: formula units

Posted: Sat Nov 10, 2018 7:10 pm
Thanks

### Re: formula units

Posted: Tue Nov 13, 2018 2:54 pm
Zubair Ahmed 1E wrote:
Arlene Linares 3A wrote:For the midterm, does anyone knows how much the units are worth when graded?

I believe both units and sig figs are each worth one point.

Thank you

### Re: formula units

Posted: Fri Nov 23, 2018 11:15 pm
Are degrees (used to describe bond angles) an SI unit?

### Re: formula units

Posted: Sun Dec 02, 2018 12:55 pm
no, degrees are not an si unit. Si unit would be a radian

### Re: formula units

Posted: Sun Dec 09, 2018 2:22 am
Are their specific units that we should be using? I usually just follow the units given in the problem, but as I was working through one the answer was given in mL instead of L.