In today’s class, we worked on the introduction to moles. A mole is defined as 6.02 x 1023 (Avogadro's number)
particles [Avogadro's number corresponds to the number of atoms as there are in
12g of 12C]. These particles are the smallest units in the sample and could be
made of atoms (sodium), ions
(fluoride), molecules (water), or 'formula units' (potassium chloride).
1 mole of different substances all have different masses. For
example, 1 mole of water does not weigh the same as 1 mole of sodium. Due to
the size of their smallest particles, the mass of one mole varies.
The equation that can be used to calculate moles is as follows:
Moles = Mass/Molar mass
To calculate the number
of particles:
# of particles = # of moles/Avogadro's number
How many moles are present in 18g of H2O?
1.
Add up the molar mass of H2O
H=1; O=16 à 16+2(1) =18
The total molar mass is 18
2. Divide the actual mass by the molar
mass
18/18= 1 mole
There is 1 mole of H2O in 18g.
How many water molecules is this?
Water molecules are the particles à use
the number of particles equation
# of particles= 1 x 6.02 x 1023
= 6.02 x 1023 water molecules
How many hydrogen atoms?
In each H2O molecule, there are two
hydrogen atoms.
Multiply
two by Avogadro's number to get the number of hydrogen atoms
2 x 6.02
x 1023 = 1.204 x 1024 hydrogen atoms
How many moles are there in 200g of CaCO3?
1.
Calculate molar mass
Ca=40; C=12; O=16 --> 40+12+16(3) =100
The total molar mass is 100
2.
Divide actual mass by molar mass
200/100= 2 moles of
Then, we performed a counting and weighing atoms lab. We were to weigh certain substances
in a weighing boat (trying to get approximately the same volume for each
compound) and then work out the number of moles in that amount of the
substance. Below is a section of the data table.*
|
Name
of substance
|
Molar
mass
|
Mass
of substance
(±.01)
|
Number
of moles
(calculated)
|
Type
of particles in sample
|
Number
of particles
(calculated)
|
|
Carbon
|
12
|
.20
|
.017
|
Atoms
|
1.0234 x 1022
|
|
Potassium chloride (KCl)
|
74.5
|
.31
|
.004
|
Formula units
|
2.408 x 1021
|
|
Sugar (C6H12O6)
|
180
|
.36
|
.002
|
Molecules
|
1.204 x 1021
|
*Results may vary depending on how much of
the substance was weighed
In conclusion, we learned what a mole is and how to calculate the
moles in a substance given its chemical formula and weight. We learned about
Avogadro’s number and its role in working out the number of particles in a
substance. Lastly, we learned to identify which type of particle is the
smallest.
Images from: education-portal.com;
www.bbc.co.uk; faculty.clintoncc.suny.edu; www.webelements.com;
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