The equation can also be used to calculate mass and molar mass, using the following equations:
and
The following diagram may help to remember the relationship between these three variables. You need to imagine that the horizontal line is like a 'division' sign and that the vertical line is like a 'multiplication' sign. So, for example, if you want to calculate 'M', then the remaining two letters in the triangle are 'm' and 'n' and 'm' is above 'n' with a division sign between them. In your calculation then, 'm' will be the numerator and 'n' will be the denominator.
Calculate the number of moles of copper there are in a sample that weighs
.
There are 2 moles of copper in the sample.
You are given a 5 mol sample of sodium. What mass of sodium is in the sample?
M
Therefore,
The sample of sodium has a mass of
.
Calculate the number of atoms there are in a sample of aluminium that weighs
.
Number of atoms in 3 mol aluminium
There are
aluminium atoms in a sample of
.
Some simple calculations
Calculate the number of moles in each of the following samples:
of calcium
of manganese
of aluminium
A lead sinker has a mass of
.
Calculate the number of moles of lead the sinker contains.
How many lead atoms are in the sinker?
Calculate the mass of each of the following samples:
magnesium
lithium
atoms of silicon
Molecules and compounds
So far, we have only discussed moles, mass and molar mass in relation to
elements . But what happens if we are dealing with a molecule or some other chemical compound? Do the same concepts and rules apply? The answer is 'yes'. However, you need to remember that all your calculations will apply to the
whole molecule . So, when you calculate the molar mass of a molecule, you will need to add the molar mass of each atom in that compound. Also, the number of moles will also apply to the whole molecule. For example, if you have one mole of nitric acid (
), it means you have
molecules of nitric acid in the sample. This also means that there are
atoms of hydrogen,
atoms of nitrogen and (
)
atoms of oxygen in the sample.
In a balanced chemical equation, the number that is written in front of the element or compound, shows the
mole ratio in which the reactants combine to form a product. If there are no numbers in front of the element symbol, this means the number is '1'.
e.g.
In this reaction, 1 mole of nitrogen reacts with 3 moles of hydrogen to produce 2 moles of ammonia.
Calculate the molar mass of
.
Hydrogen
; Sulphur =
; Oxygen
Calculate the number of moles there are in
of
.
Convert mass into grams
Calculate the molar mass of
.
There are
of magnesium chloride in a
sample.
Barium chloride and sulphuric acid react according to the following equation to produce barium sulphate and hydrochloric acid.
If you have
of
...
What quantity (in g) of
will you need for the reaction so that all the barium chloride is used up?
What mass of
is produced during the reaction?
According to the balanced equation, 1 mole of
will react with 1 mole of
. Therefore, if
of
react, then there must be the same number of moles of
that react because their mole ratio is 1:1.
(answer to 1)
According to the balanced equation, 2 moles of
are produced for every 1 mole of the two reactants. Therefore the number of moles of
produced is (
), which equals
.
(answer to 2)
Group work : understanding moles, molecules and avogadro's number
Divide into groups of three and spend about 20 minutes answering the following questions together:
What are the units of the mole? Hint: Check the definition of the mole.
You have a
sample of iron sulphide (
)
How many
moles of
are there in the sample?
How many
molecules of
are there in the sample?
What is the difference between a mole and a molecule?
The exact size of
Avogadro's number is sometimes difficult to imagine.
Write down Avogadro's number without using scientific notation.
How long would it take to count to Avogadro's number? You can assume that you can count two numbers in each second.
Khan academy video on the mole - 1
More advanced calculations
Calculate the molar mass of the following chemical compounds:
How many moles are present in:
of
SO
of
molecules of
?
For a sample of
of potassium bromide (
), calculate...
the number of moles of
ions
the number of moles of
ions
You have a sample containing
of calcium chloride.
What is the chemical formula of calcium chloride?
How many calcium atoms are in the sample?
Calculate the mass of:
of
of
sulphur reacts with an unknown quantity of zinc according to the following equation:
What mass of zinc will you need for the reaction, if all the sulphur is to be used up?
What mass of zinc sulphide will this reaction produce?
Calcium chloride reacts with carbonic acid to produce calcium carbonate and hydrochloric acid according to the following equation:
If you want to produce
of calcium carbonate through this chemical reaction, what quantity (in g) of calcium chloride will you need at the start of the reaction?
Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you.
Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
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