formula units [ENDORSED]

[Natalie_Martinez_1I]

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?

[Ismail 1F]

Yes, you can use Avogadro's number to convert to formula units.

[LilianKhosravi_1H]

Yeah I had the same question but I think it just means number of atoms.

[Tiffany Tufenkjian 1E]

I had this question too, I don't think it will be unclear like this on the test.

[Kelly Zhang 1L]

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.

[Saachi_Kotia_4E]

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.

[Chem_Mod]

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

[Yiwen Chen-3G]

Yes I think I have the same problem. Thanks for answers above!

[Abby-Hile-1F]

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.

[Sarah Zhao 4C]

Formula units is the equivalent of molecules for different compounds.

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

[Yousif Jafar 1G]

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.

[Madeline Lequang 1G]

Does anybody know what unit "pm" is? I'm doing the homework right now and I'm not sure what it stands for.

[Sophia Ding 1B]

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.

[Simran Athwal-Dis 3A]

Hello! I had a question regarding atomic masses. Do we round the atomic masses on the periodic table or leave them as is?

[Rosha Mamita 2H]

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

[Zack Barta 3I]

Thank you!

[305008749]

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.

[Simran Athwal-Dis 3A]

Thank you for the feedback!

[Danny Elias Dis 1E]

What was the unit of measurement only used by chemists, also known as 10 to the -10 power?

[Simran Athwal-Dis 3A]

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?

[davidbakalov_lec2_2L]

I believe the unit you are thinking of is the Ãngström, 1Ã = 10^(-10).

[BenJohnson1H]

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

[Henry Dudley 1G]

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.

[Henry Dudley 1G]

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.

[Sapna Ramappa 1J]

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. :)

[Roberto Gonzalez 1L]

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?

[Jordan Lo 2A]

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?

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

[Dhwani Krishnan 1G]

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?

[Elizabeth Kim 4E]

Any ionic or covalent solid compound not just salts

[Daniel Bowen 3I]

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

[Andreana Vetus 1A]

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.

[Andreana Vetus 1A]

I have a simple question regarding basic chemistry:

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

[LG2019]

So is the term 'formula units' only relevant when talking about compounds?

[Rami_Z_AbuQubo_2K]

Wait, so when it is talking about formula units, it does not specifically mean atoms/molecules, right?

[Chem_Mod]

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.

[Dina Geotas 4A]

Yes I think you just use Avogadro's number to find the number of atoms or molecules!

[inlovewithchemistry]

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!

[404817859]

I believe a formula unit is the empirical formula incase that makes it easier to understand

[NatBrown1I]

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.

[Anusha 1H]

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.

[Simran Athwal-Dis 3A]

Hi, I had a quick question. How do we check how many times we posted on Chemistry Community? Do we go on our profile?

[Simran Athwal-Dis 3A]

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!

[Simran Athwal-Dis 3A]

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!

[Simran Athwal-Dis 3A]

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!

[Yvonne Du]

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.

[lukezhang2C]

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!

[Jessica Dharmawan 1G]

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.

[Arlene Linares 3A]

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?

[Simran Athwal-Dis 3A]

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

Thank You!

[Simran Athwal-Dis 3A]

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.

[Simran Athwal-Dis 3A]

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?

[Hilda Sauceda 3C]

The numbers on the numerator are constants which will always be given and they are found on the "constants and Equations" worksheet.

[905096106]

Formula Units are the same thing as molecules except for compounds with ionic bonds.

[Zack Barta 3I]

Thanks!

[Jennifer Lathrop 1F]

Yes, it just means number of atoms which means you use 6.022x10^23

[Celine Hoh 2L]

Yes, which is the Avogadro Number.

[Aria Soeprono 2F]

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.

[Simran Athwal-Dis 3A]

[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!

[taywebb]

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)

[Simran Athwal-Dis 3A]

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?

[Arlene Linares 3A]

For the midterm, does anyone knows how much the units are worth when graded?

[Zubair Ahmed 1L]

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.

[Zack Barta 3I]

Thanks

[Zack Barta 3I]

Thanks

[Zack Barta 3I]

Thanks

[Arlene Linares 3A]

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

[Danny Elias Dis 1E]

Are degrees (used to describe bond angles) an SI unit?

[105002507]

no, degrees are not an si unit. Si unit would be a radian

[904837647]

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.

[kim 2I]

Usually answers should be written in the same unit as the unit presented in the question. Since the unit difference was only a conversion (L to mL), I think both answers would be acceptable as long as the numerical value is correct.