Formula Mass and Molar Mass of Compounds
Summary
TLDRThis 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
🧪 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.
📚 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.
🔍 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.
Mindmap
Keywords
💡Formula Mass
💡Molar Mass
💡Atomic Mass Unit (AMU)
💡Molecular Mass
💡Molecular Weight
💡Avogadro's Number
💡Ionic Compounds
💡Mole Concept
💡Sodium Chloride (NaCl)
💡Chemical Formula
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
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