Formula Mass and Molar Mass of Compounds

Summary

This educational video explains the concepts of formula mass and molar mass of compounds. It illustrates how to calculate the formula mass of a compound like formaldehyde (CH2O) by summing the atomic masses of its constituent elements. The video also clarifies that molar mass, expressed in grams per mole, is numerically equivalent to the formula mass in AMU. It demonstrates converting mass to moles using molar mass and then to the number of molecules or formula units using Avogadro's number, exemplified with sodium chloride.

Takeaways

• 🔍 The video discusses the concept of formula mass and molar mass of compounds, using glucose tablets as an example.
• 📐 Formula mass is analogous to atomic mass for elements, representing the average mass of a molecule or formula unit of a compound.
• 🔬 The unit for formula mass is the atomic mass unit (AMU), which is defined as one twelfth of the mass of a carbon-12 atom.
• 📝 Formula mass is calculated by summing the products of the number of atoms of each element in a compound and their respective atomic masses.
• 🌐 Synonyms for formula mass include molecular mass and molecular weight, all referring to the same concept.
• 🧪 Molar mass is the mass of one mole of a compound, typically expressed in grams, and is numerically equivalent to the formula mass in AMU.
• 🔄 To find the number of molecules or formula units in a sample, one can convert the mass of the compound to moles using molar mass, then to the number of entities using Avogadro's number.
• 📚 Avogadro's number (6.022 x 10^23) represents the number of entities in one mole of a substance.
• ⚖️ An example is provided to calculate the number of sodium chloride formula units in a given mass, illustrating the process of converting mass to moles and then to formula units.
• 📈 The video emphasizes the importance of understanding molar mass and formula mass to count molecules by weighing a sample of a compound.

Q & A

What is formula mass, and how is it similar to atomic mass?

Formula mass is the average mass of a molecule (for molecular compounds) or a formula unit (for ionic compounds) expressed in atomic mass units (AMU). It is analogous to the atomic mass of an element, which represents the average mass of an atom in AMU.

What are the synonyms for formula mass?

Synonyms for formula mass include molecular mass and molecular weight. These terms can be used interchangeably and always refer to the same concept.

How do you calculate the formula mass of a compound?

To calculate the formula mass, you multiply the number of atoms of each element in the compound by its atomic mass, then sum the results for all elements in the formula.

What is the formula mass of formaldehyde (CH2O)?

The formula mass of formaldehyde (CH2O) is 30.0260 AMU. This is calculated by adding the atomic mass of carbon (12.0107 AMU), hydrogen (1.00794 AMU × 2), and oxygen (15.9994 AMU).

What is molar mass, and how is it related to formula mass?

Molar mass is the mass of one mole of a compound, typically expressed in grams per mole. It is numerically equivalent to the formula mass of the compound but is measured in grams rather than AMU.

What is Avogadro's number, and why is it important in molar mass calculations?

Avogadro's number is 6.022 × 10^23, representing the number of atoms, molecules, or formula units in one mole of a substance. It allows us to relate the molar mass of a substance to the actual number of particles present in a sample.

How do you convert the mass of a compound into the number of molecules or formula units?

First, convert the mass of the compound into moles using its molar mass. Then, use Avogadro's number to convert the number of moles into molecules or formula units.

How do you calculate the molar mass of sodium chloride (NaCl)?

The molar mass of NaCl is calculated by adding the atomic masses of sodium (22.989770 grams per mole) and chlorine (35.453 grams per mole), which results in 58.443 grams per mole.

How can you calculate the number of formula units in a given mass of NaCl?

First, convert the mass of NaCl from kilograms to grams. Then, divide by the molar mass of NaCl to get the number of moles. Finally, multiply the number of moles by Avogadro's number to get the number of formula units.

What is the result of calculating the number of formula units in 1.254 kg of NaCl?

The number of formula units in 1.254 kg of NaCl is approximately 1.292 × 10^25 formula units. This is determined by converting the mass to moles using the molar mass of NaCl and then using Avogadro's number to find the total formula units.

Outlines

00:00

🧪 Understanding Formula Mass and Molar Mass

The video begins by introducing the concepts of formula mass and molar mass of compounds. It explains that formula mass is analogous to atomic mass for elements, representing the average mass of a molecule in molecular compounds or a formula unit in ionic compounds. The unit for formula mass is the atomic mass unit (AMU), which is defined as one twelfth of the mass of a carbon-12 atom. The video also clarifies that molecular mass, molecular weight, and formula mass are interchangeable terms. The process of calculating the formula mass of a compound involves multiplying the number of atoms of each element in the compound's chemical formula by their respective atomic masses and then summing these products. An example calculation for formaldehyde (CH2O) is provided, resulting in a formula mass of 30.0260 AMU. The video then transitions into discussing molar mass, which is the mass of one mole of a compound, often expressed in grams.

05:00

📚 Molar Mass and Counting Molecules

This section of the video script delves into the relationship between molar mass and formula mass, stating that they are numerically equivalent, with molar mass expressed in grams per mole. The script uses the example of formaldehyde to illustrate that if the formula mass is 30.0260 AMU, then the molar mass is 30.0260 grams per mole. The video then explains how to use molar mass to count the number of molecules in a sample of a compound. The process involves converting the mass of the compound to moles using the molar mass and then using Avogadro's number to find the number of molecules or formula units. An example is given where the number of sodium chloride formula units in a 1.254 kg sample is calculated. The calculation starts by converting kilograms to grams, using the molar mass of sodium chloride (found by adding the molar masses of sodium and chlorine), and then applying Avogadro's number to find the number of formula units.

10:03

🔍 Calculating Formula Units of Sodium Chloride

The final paragraph of the script provides a detailed example of calculating the number of sodium chloride formula units in a given mass of the compound. It walks through the process of converting the mass of sodium chloride from kilograms to grams, using the molar mass to find the number of moles, and then applying Avogadro's number to determine the number of formula units. The calculation ensures that all units cancel out appropriately, leaving only the number of formula units. The video encourages viewers to perform these calculations on their own to solidify their understanding. The final answer provided is 1.292 x 10^25 formula units of sodium chloride, demonstrating the practical application of the concepts discussed in the video.

Keywords

💡Formula Mass

Formula mass refers to the average mass of one molecule of a molecular compound or one formula unit of an ionic compound. It is calculated by summing the atomic masses of all the atoms in the chemical formula. In the video, formula mass is used to demonstrate how to calculate the mass of a compound like glucose tablets, which is essential for understanding the amount of substance in a sample.

💡Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is numerically equivalent to the formula mass in atomic mass units (AMU). The video explains that molar mass is crucial for determining the number of molecules in a given mass of a compound, such as calculating the number of glucose molecules in tablets.

💡Atomic Mass Unit (AMU)

The atomic mass unit (AMU) is a unit of mass that quantifies mass on an atomic or molecular scale. It is defined as one twelfth of the mass of a carbon-12 atom. The video uses AMU to express both atomic and formula masses, highlighting its importance in chemical calculations.

💡Molecular Mass

Molecular mass is a term synonymous with formula mass, referring to the mass of a molecule. The video script uses 'molecular mass' interchangeably with 'formula mass' to describe the mass of a molecule like glucose, emphasizing the calculation process for compounds.

💡Molecular Weight

Molecular weight is another term for formula mass or molecular mass, indicating the weight of a molecule. In the video, it is mentioned as a synonym, used to describe the calculation of the mass of a compound like formaldehyde (form alahh).

💡Avogadro's Number

Avogadro's number is approximately 6.022 x 10^23, representing the number of entities (atoms, molecules, etc.) in one mole of a substance. The video discusses how Avogadro's number is used to convert moles to the number of molecules or formula units, such as calculating the number of sodium chloride formula units.

💡Ionic Compounds

Ionic compounds are formed by the electrostatic attraction between positively and negatively charged ions. The video distinguishes ionic compounds from molecular compounds by emphasizing that they form formula units rather than discrete molecules, as in the case of sodium chloride.

💡Mole Concept

The mole is a fundamental concept in chemistry that represents a collection of a specific number of particles, with that number being Avogadro's number. The video script mentions the importance of understanding the mole concept for calculating the number of molecules in a compound.

💡Sodium Chloride (NaCl)

Sodium chloride, commonly known as table salt, is used as an example of an ionic compound in the video. It is used to demonstrate how to calculate the number of formula units in a given mass, showcasing the application of molar mass and Avogadro's number.

💡Chemical Formula

A chemical formula represents the elemental composition of a compound, such as glucose (C6H12O6) or sodium chloride (NaCl). The video explains how to use the chemical formula to calculate the formula mass by multiplying the atomic masses of the constituent elements by their respective quantities.

Highlights

Introduction to formula mass and molar mass for compounds using glucose as an example.

Formula mass is analogous to atomic mass but applies to molecules or ionic compounds.

Formula mass is measured in atomic mass units (AMU), the same unit used for atomic mass.

AMU is defined as one-twelfth of the mass of a carbon-12 atom.

Formula mass, molecular mass, and molecular weight are synonyms and represent the same concept.

To calculate the formula mass, multiply the number of atoms of each element in the compound by its atomic mass and sum the results.

Example: Calculating the formula mass of formaldehyde (CH2O) by adding the atomic masses of carbon, hydrogen, and oxygen.

The formula mass of formaldehyde is calculated as 30.0260 AMU.

Molar mass refers to the mass in grams of one mole of a compound and is numerically equivalent to the formula mass in AMU.

One mole contains Avogadro’s number of molecules or formula units (6.022 × 10^23).

Example: Calculating the molar mass of sodium chloride (NaCl) by summing the molar masses of sodium and chlorine.

The molar mass of NaCl is calculated as 58.443 grams per mole.

Steps to convert mass of a compound to the number of formula units by first finding moles, then using Avogadro's number.

Example: Calculating the number of formula units in a 1.254 kg sample of sodium chloride.

Final answer: 1.292 × 10^25 formula units of sodium chloride, showing the complete process of converting mass to the number of formula units.

Transcripts

hey everyone in this video we're going

to talk about the formula mass and molar

mass of compounds so shown in this

Photograph here are a few glucose

tablets and remember when when we were

studying the atomic mass and the molar

mass of elements we were able to take a

sample of an element and just by

weighing it we could figure out how many

atoms are in that sample well using

formula mass and molar mass for

compounds we can actually do the same

thing uh with a with a compounds just

like these glucose tablets here we can

actually weigh these glucose tablets and

then using a couple of Handy Dandy

calculations we can figure out how many

molecules of glucose are in a given

sample of glucose or any compound for

that matter so the formula mass of a

compound is very much analogous to the

atomic mass of an element the formula

mass is actually the average mass of a

molecule in the case of molecular

compounds or formula unit in the case of

ionic compounds and the unit for formula

mass is the atomic mass unit or AMU and

you might be familiar with the AMU the

AMU is the same unit that we use to

express the atomic mass of elements and

remember the AMU is defined as one 12th

of the mass of a carbon 12 atom so

that's very important and a couple of

synonyms for formula mass are molecular

mass and molecular weight so anytime you

throw around either of these terms

molecular mass molecular weight or

formula mass you're always talking about

the same thing no matter which term you

use and to get the formula mass to

calculate the formula mass of any

compound what you're going to do is the

following you're going to take the

number of atoms in the first element of

your chemical formula and you're going

to multiply it by the atomic mass of

your first element and then you're going

to take that product and you're going to

add that to the product of the number of

atoms in the second element of your

chemical formula time the atomic mass of

your second element and then you're

going to keep going until you run out of

elements in your chemical formula so

with that in mind let's do an example

where we calculate the formula mass of a

compound so this says to calculate the

formula mass of form Malahide which has

the formula

ch2o so let's go ahead and do that so

what we're going to do is we're going to

take the atomic mass of our first

element which is carbon and the atomic

mass of carbon is 12

0.107

AMU and we're going to multiply it by

the number of atoms in the in the uh the

number of carbon atoms so that's just

one so we can just leave that alone and

then we're going to add that to the

atomic mass of hydrogen which is

1.00794 AMU so

1.00794

AMU and we're going to multip mly that

by two the number of hydrogen atoms in

form

Malahide and then finally we're going to

add the molar M excuse me the atomic

mass of oxygen which is

15.9994 AMU so

15.9994

amuu times the number of oxygen atoms

which again is one so we can just leave

that alone and if you carry this

calculation out yourself which I highly

encourage then the answer you're going

to arrive at is

30

0260

AMU so this is

the formula mass of form alahh and this

is how you would go about calculating

the formula mass of any

compound so with that in mind I'd like

to talk about the molar mass of a

compound and the molar mass of a

compound is the mass which is usually

given in grams of one mole of a compound

so if you're unfamiliar with the mole it

might be a good time to brush up on the

mole concept which I do have a video for

I'll uh I'll provide a link for it down

there in the uh description box but

again so yeah the formula mass is the

mass of one mole of a compound and

remember that one mole of anything is

avagadro's number of that thing

avagadro's number being

6.022 * 10^ 2 3 so if I have a mole of

toothpicks that's

6.022 * 10 23rd toothpicks any mole of

anything is always going to be 6.022 *

10 23rd of that thing so for instance if

I have a mole of formaly as I saw

earlier that's going to be 6.022 * 10

23rd form Malahide molecules and the uh

the beautiful thing the nice thing about

the molar mass is that it's actually

numerically equivalent to the

corresponding compounds formula mass in

AMU so uh for instance we saw earlier

that the uh the formula mass of form

Malahide was 30.02 60 AMU uh that means

that the average form Malahide molecule

has a mass of 30.02 60 AMU and that also

means that the molar mass of formaly so

the mass of one mole 6.022 * 10 23rd of

form alhy molecules is

30.02 60 G so we say that the molar mass

of formaly is 30.02 60 grams per

mole so with the molar mass and the uh

formula mass we can actually we're in a

position now where we can count

molecules by weighing a sample of a

compound so we can start with the mass

and we can get all the way to the number

of molecules in that sample so we're not

really going to do it directly because

uh we need a couple of steps along the

way uh we're going to do it in a

two-step process what we're going to do

is we're going to start with the mass of

the compound and we're going to convert

that to the number of moles of the

compound we're going to accomplish that

by using the molar mass of the compound

and then once we have the mol uh the

amount of the compound in moles we can

actually convert that to the number of

molecules or formula units in the case

of bionic compounds uh using avagadro's

number so let's go through an example

where we do this whole thing so the

example says to calculate the number of

sodium chloride formula units in a 1.254

kilogram sample of sodium chloride

remember sodium chloride is an ionic

compound so it doesn't necessarily form

molecules per se so the correct

terminology is Formula units so that's

why i' I've included that in the example

uh so again so what we're going to do is

we're going to start with our given

information which is our

1.254 kilograms so it's

1.254 kilogram

of

Na

oops 1.254 kilograms of

NAC and the molar mass like I said it's

usually given in grams per mole so we

got to take that kilograms and we got to

convert it to

grams so one kilogram of

NAC kilo is the uh is the prefix that

corresponds to 10 the 3 so that means

that one kilogram of a NAC is going to

be 10 the 3 or

1,00 gr of

Na

CL so now that we have grams of NAC we

can use the molar mass of NAC which is

again is going to be given in grams per

mole so what I'm going to do is I'm

going to put grams of NAC on the

bottom and I'm going to put one mole of

Na CL on

top so now what we have to do is we

actually have to calculate the molar

mass of NAC so what you're going to do

is you're going to refer to your

periodic table and you're going to see

those atomic masses of NAC or of of

sodium and chlorine rather and those

atomic masses are going to be equivalent

to to the corresponding elements molar

masses in grams per mole so we're simply

going to add those together okay so the

molar mass of sodium is it right here

the molar mass of sodium is

22

89770 and this is grams per

mole and we're going to add that to the

molar mass of chlorine which is

35.453 gam per mole

and once we add those together we're

going to carry it out to three decimal

places which is the fewest and that's

going to give us 58.4

43 gr per

mole so what I'm going to do is I'm

going to stick that 58.4 43 grams per

mole in right here so instead of writing

it a second time I'm just going to draw

that little arrow there so we know what

we're talking about here so now we have

converted to moles of sodium chloride

but we're not quite finished yet we have

to take that moles uh and we have to

convert it to formula units and we do so

again using avagadro's number so I'm

going to put my one mole of NAC on the

bottom and I'm going to put my avagadro

number on top which is that

6022 time 10 to the 23r

formula units of sodium chloride so um

it's going to be I'll just put it in up

here formula units which I'll just

abbreviate Fu of

NAC whoops let me try that

again have to write really

small

okay so let's go ahead and make sure all

of our units cancel so we have kilograms

canceling with kilograms we have grams

can canceling with gr moles canceling

with moles and we're left with nothing

but formula units of sodium chloride and

that's going to give us our final answer

is going to be again I encourage you to

do these calculations on your own so uh

please pause the video and do it

yourself before you look at the uh

before you look any further and your

final answer is going to be 1.

292 * 10

25th formula unit

of sodium

chloride so there you have it it's very

very similar to uh calculating the uh

the amount of atoms of a sample of a

given element uh all you have to do is

the only extra step you would have to do

is just add together the uh the molar

masses of your individual elements that

compose your compound so all right I

hope this video helped you out a little

bit and um take it easy