Calculating Mole Grade 10 | Part 1
Summary
TLDRThis chemistry lesson focuses on calculating moles using the formula n = m/M, where n is the number of moles, m is the given mass, and M is the molar mass. Examples are provided for CO2, H2O, and H2SO4 to demonstrate how to find moles from mass and vice versa. The instructor also introduces a triangle method to rearrange the formula for different calculations, including determining mass from moles and molar mass.
Takeaways
- 🔍 The formula n = m/M is used to calculate the number of moles (n), where m is the given mass and M is the molar mass.
- 📚 The molar mass (M) is the mass of one mole of a substance, which can be found on the periodic table and is measured in grams per mole.
- 🧪 Examples are used to demonstrate how to calculate the number of moles in a given mass of a substance, such as CO2, H2O, and H2SO4.
- 📈 The molar mass of a compound is calculated by summing the atomic masses of all the atoms in the compound's formula.
- ⚖️ For CO2, the molar mass is calculated as 12 (carbon) + 2*16 (oxygen) = 44 grams per mole.
- 💧 For H2O, the molar mass is 2*1 (hydrogen) + 16 (oxygen) = 18 grams per mole.
- 🌊 For H2SO4, the molar mass is 2*1 (hydrogen) + 32 (sulfur) + 4*16 (oxygen) = 98 grams per mole.
- 🔄 The formula can be rearranged to solve for different variables, such as calculating mass when given moles or molar mass.
- 📉 The concept of a 'triangle' is introduced to help remember the relationships and rearrangements of the formula n = m/M.
- 🔢 Practice problems are provided to reinforce learning and apply the formula in various scenarios, including calculating mass from moles and vice versa.
Q & A
What does the formula n = m/M represent?
-The formula n = m/M represents the relationship between the number of moles (n), the mass (m), and the molar mass (M) of a substance.
What is the difference between the lowercase 'm' and uppercase 'M' in the context of the formula?
-In the formula, the lowercase 'm' represents the given mass of a substance, while the uppercase 'M' represents the molar mass of that substance.
How is the molar mass of CO2 calculated?
-The molar mass of CO2 is calculated by adding the atomic mass of one carbon atom (12) and two oxygen atoms (16 each), resulting in a total of 44 grams per mole.
What is the molar mass of H2O?
-The molar mass of H2O is calculated by adding the mass of two hydrogen atoms (1 each) and one oxygen atom (16), resulting in a total of 18 grams per mole.
How many moles are in 88 grams of CO2?
-Using the formula n = m/M, and knowing the molar mass of CO2 is 44 grams per mole, there are 2 moles in 88 grams of CO2.
What is the molar mass of H2SO4?
-The molar mass of H2SO4 is calculated by adding the mass of two hydrogen atoms (1 each), one sulfur atom (32), and four oxygen atoms (16 each), resulting in a total of 98 grams per mole.
How many moles are in 54 grams of H2O?
-Using the formula n = m/M, and knowing the molar mass of H2O is 18 grams per mole, there are 3 moles in 54 grams of H2O.
How many moles are in 49 grams of H2SO4?
-Using the formula n = m/M, and knowing the molar mass of H2SO4 is 98 grams per mole, there are 0.5 moles in 49 grams of H2SO4.
How can the formula n = m/M be rearranged to solve for mass (m)?
-To solve for mass (m), the formula can be rearranged to m = n * M, where n is the number of moles and M is the molar mass.
How can the formula n = m/M be rearranged to solve for molar mass (M)?
-To solve for molar mass (M), the formula can be rearranged to M = m/n, where m is the mass and n is the number of moles.
What is the mass of 3 moles of CO2?
-Using the rearranged formula m = n * M, and knowing the molar mass of CO2 is 44 grams per mole, the mass of 3 moles of CO2 is 132 grams.
Outlines
🔬 Chemistry Lesson: Understanding Moles and Molar Mass
This paragraph introduces the concept of moles and molar mass in chemistry. The distinction between lowercase 'm' for mass and uppercase 'M' for molar mass is clarified. The formula n = m / M is introduced, where n represents the number of moles, m is the given mass, and M is the molar mass. The molar mass of CO2 is calculated as an example, highlighting the importance of using the periodic table to find the mass of individual elements (carbon = 12, oxygen = 16) and summing them to find the molar mass of the compound (44 g/mol). The process is repeated for H2O and H2SO4, emphasizing the method of calculating moles from given mass and vice versa.
📐 Using the Triangle Method to Manipulate Chemical Formulas
The paragraph explains how to use a triangle method to rearrange the formula n = m / M to solve for different variables. It demonstrates how to isolate n, m, or M by manipulating the formula accordingly. The method is applied to calculate the mass of a given number of moles, such as determining the mass of 3 moles of CO2. The molar mass of CO2 is used again (44 g/mol), and the calculation results in 132 grams for 3 moles. The lesson continues with more examples, including calculating the mass of 9 moles of NaOH, where the molar mass is found by adding the atomic masses of sodium (23), oxygen (16), and hydrogen (1), resulting in 40 g/mol.
🧪 Calculating Moles from Given Mass: An Example with CaCO3
The final paragraph focuses on calculating the number of moles from a given mass, using the formula n = m / M. The example provided is 50 grams of calcium carbonate (CaCO3). The molar mass of CaCO3 is calculated by summing the atomic masses of calcium (40), carbon (12), and three oxygen atoms (3 x 16), resulting in 100 g/mol. Using the formula, the calculation shows that 50 grams of CaCO3 is equivalent to 0.5 moles. This section reinforces the concept of molar mass and its application in determining the quantity of a substance in terms of moles.
Mindmap
Keywords
💡Mole (n)
💡Mass (m)
💡Molar Mass (M)
💡CO2
💡H2O
💡Formula
💡Periodic Table
💡Atomic Mass
💡Mole Concept
💡Stoichiometry
💡Example Problems
Highlights
Introduction to the formula n = m/M, where n stands for moles, m for mass, and M for molar mass.
Explanation of the difference between lowercase 'm' for mass and uppercase 'M' for molar mass.
Molar mass is the mass of a substance per mole, measured in grams per mole.
Example calculation of moles in 88 grams of CO2 using the formula n = m/M.
Calculation of molar mass for CO2 as 44 grams per mole.
Explanation of how to calculate moles when given mass and molar mass.
Example calculation of moles in 54 grams of H2O using the formula n = m/M.
Calculation of molar mass for H2O as 18 grams per mole.
Example calculation of moles in 49 grams of H2SO4 using the formula n = m/M.
Calculation of molar mass for H2SO4 as 98 grams per mole.
Introduction to the concept of using a triangle to rearrange the formula for different calculations.
Explanation of how to calculate mass when given moles and molar mass.
Example calculation of mass in three moles of CO2.
Calculation of mass for three moles of CO2 as 132 grams.
Example calculation of mass for nine moles of NaOH.
Calculation of molar mass for NaOH as 40 grams per mole.
Example calculation of moles in 50 grams of CaCO3.
Calculation of molar mass for CaCO3 as 100 grams per mole.
Final example calculation of moles in 50 grams of CaCO3 resulting in 0.5 moles.
Transcripts
hey guys hope you're well so this lesson
is all going to be about this formula
over here so the n stands for mole the
now you see there's a small M and
there's a capital M don't confuse those
okay so the small m is the mass
or let's say the given Mass okay this
will all make sense when we do some
examples that's the given mass and then
the capital M is called
molar mass
okay and what that is is it's the mass
on the periodic
table
and it's measured in grams
per mole so you write it like that okay
this will make sense as we do some
examples so what I want us to do now is
answer the following question
so this question says how many moles are
there in 88 grams of CO2 okay now by the
way this given mass is also measured in
grams so what we can do is we use this
formula over here okay so we set n
equals to M over capital M now look how
easy this is they gave us 88 grams so
that is the small M the small m is the
given mass and so you're going to say 88
over now to calculate this part over
here this is the mass on the periodic
table so if you look at CO2 well what we
can see is that that is going to be one
carbon atom okay so it's one carbon atom
plus and then there's two oxygens over
here so two oxygens okay and so that
would be one carbon atom which has a
mass of 12. and then two oxygens would
now oxygen has a mass of 16.
so if you work this out correctly you
should get 44.
and then remember that the units of
capital M would be
um
grams per mole so you're going to say
grams per mole and so you're gonna go
put that number down here at the bottom
and then if you had to calculate this
you're going to end up with two
mole
so here's another example and then as we
go along in this lesson I'm going to
give you more questions like this but
then I'm also going to start changing
the questions up where you're going to
have to start using this formula in
different ways
so it says how many moles are there in
54 grams of H2O okay so we're going to
say n equals to M over capital M now
remember that the small m is the given
Mass
the Big M is the molar mass
which is from the periodic table
and then n is the mole so we're going to
say uh n is equal to another given mass
is 54. that's what they gave us 54.
now the molar mass you have to go get
that on the periodic table so this is
H2O so that means
um the the molar mass of H2O would be
there's two hydrogens there's two
hydrogens
and there is one oxygen one oxygen and
so the mass of that would be 2
multiplied by one
plus 1 multiplied by oxygen which is 16.
and if you had to work that out you
would get 18 and then the the units is
grams per mole so I need to say I need
to say 18 grams per mole so I put a 18
over there and if you had to go work
this out you'd end up with three mole
here's another one so how many moles are
there in 49 grams of h2so4 okay so we
know that to calculate moles you're
going to say n equals to M over capital
M now remember small m is the given Mass
which must always be measured in grams
and then the capital M is the molar mass
which is the mass that you get on the
periodic table
and then n is the mole okay so the given
mass is 49.
now h2so4 so what that is is
um to work out the molar mass of h2so4
well there is
um two hydrogens so two hydrogens there
is one sulfur atom okay so let's just
write that a bit better one sulfur atom
and four oxygen atoms four oxygens and
so to work out the mass that would be
two times one because each hydrogen has
a mass of one
um one multiplied by sulfur's mass which
is 32 and then four oxygens each oxygen
has a mass of Sixteen and if you had to
go calculate that
you end up with 98 now the units of that
is grams per mole so you could put 98
over there and if you had to go
calculate that you're going to get 0
comma five
Mo now in the next questions I'm going
to show you um the next question coming
up after this one how to change this
formula and use it in different ways
okay so let's do that
so what we can do is we can make a
triangle so you know the triangles that
I've showed you in previous chapters
like maybe in electricity we've got
these triangles where we've got a v i r
or maybe you've seen other ones like WV
and Q or maybe you've seen uh q i and T
for example now when we have triangles
like that it makes it easier to work
with them okay and to do different
things so here you see this one's at the
top so the one that's at the top is
always the top part of the triangle okay
and then the other two you could just
put at the bottom so the end you could
put there and then the capital M you
could put there so now
you could make a whole bunch of
different formulas let's say you're
trying to get this one by itself
well
we know that if that one's at the top
then the other two at the bottom are
next to each other so you would multiply
them like that okay or maybe
you want to get this one by itself well
that one you wouldn't really need to get
because that one's the one that's on the
periodic table okay but let's just say
maybe they gave you a weird question uh
where oh no I don't think they'll do
that so don't worry about that one and
then obviously to work out this one over
here
oh no let me actually go back to this
one they could sometimes do something
weird where they give you like a made-up
molecule that is not on the periodic
table
and then they ask you to calculate this
part
well to do that you'll just say
um this is at the top and this is at the
bottom so that's at the top that's at
the bottom and then lastly
if we need to calculate this one well we
know how to do that one already because
this m is at the top
and then the Big M is at the bottom and
then you just get back to this formula
over here okay so you need to know how
to use all three of these and so for the
remainder of this lesson I'm going to
give you some questions
um that's going to help you practice the
different types
so here's our next question so it says
determine the mass
in three moles of CO2 okay so we know
that we've got these formulas okay now
we know that n stands for mole the small
m stands for mass or given Mass if they
give you a mass and then capital M is
the molar mass
now remember that the molar mass is the
one that is on the periodic table so
they want us to calculate
the the the mass
not the molar mass that just means the
normal Mass so that's this one okay so
we need to get a formula with this one
and so that's over here
and so we could say that that mass is
equal to the number of moles multiplied
by the molar mass so that's going to be
equal to 3 because they said there's
three moles multiplied now the molar
mass is from the periodic table so to
calculate the molar mass of CO2
well there is going to be one carbon
atom one carbon atom and then there's
going to be two oxygen atoms so the mass
would be 1 times 12.
plus 2 times the mass of oxygen which is
16 and that's going to give you 44 grams
per mole so you can put 44 of here and
if you had to go work that out
you would end up with 132 grams
oh just like that yeah you're just going
to say 132 grams you're not going to say
grams per mole the only time you say
grams per moles when you're working out
the capital M which we've just done here
on the periodic table so for this one
you just say grams okay let's do some
more examples
this one says determine the mass of 9
mole of NaOH so if we have our triangle
over here
then if they want us to calculate mass
well that's this one over here so that's
going to be n multiplied by capital M
okay so we're going to use that formula
and so the number of moles is nine
and then to get the
um to get the sorry you need to get the
mass on the periodic table so n
a whoopsie why am I writing so weird n a
o h well that's going to be 1 in a atom
you can see one in a plus one oxygen
plus one hydrogen plus one hydrogen and
so that's going to be the mass of n a 23
the mass of oxygen 16 and the mass of
hydrogen is one so that's going to be 40
grams
per mole and so we could say 9 times 40
and that's going to be 360 grams
here's our last question so it says how
many moles are there in 50 grams of
CaCO3 okay so if we have that triangle
then they want the number of moles now
so they want this so number of moles is
equal to whatever's at the top divided
by the capital M which is molar mass
so they remember that n is Mo
m is the given Mass
and here they've given it to us and then
capital M is the molar mass molar mass
which is on the periodic table periodic
table so we're going to say n equals to
M over capital M and so the mass is
going to be 50.
to go work out the molar mass of calcium
carbonate or CaCO3
then that's going to be one calcium atom
one calcium
plus one carbon
plus three oxygens
okay and so that's going to be one
calcium which is 40 grams
per mole plus one carbon which is 12.
plus three oxygens now each oxygen is
16. so if you had to go calculate this
you get a hundred
grams
per mole so that's going to be over a
hundred and so if you had to go work
this out you're going to end up with
zero comma five
mole
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