The equation can also be used to calculate mass and molar mass, using the following equations:
$$m=n\times M$$
and
$$M=\frac{m}{n}$$
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
$127\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .
$$n=\frac{m}{M}$$
$$n=\frac{127}{63,55}=2$$
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?
$$m=n\times M$$
M
${}_{\mathrm{Na}}=22,99\phantom{\rule{2pt}{0ex}}\mathrm{g}\xb7\mathrm{mol}{}^{-1}$
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 (
$\mathrm{HNO}{}_{3}$ ), it means you have
$6,022\times {10}^{23}$molecules of nitric acid in the sample. This also means that there are
$6,022\times {10}^{23}$atoms of hydrogen,
$6,022\times {10}^{23}$atoms of nitrogen and (
$3\times 6,022\times {10}^{23}$ )
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.
${\mathrm{N}}_{2}+3{\mathrm{H}}_{2}\to 2\mathrm{N}{\mathrm{H}}_{3}$
In this reaction, 1 mole of nitrogen reacts with 3 moles of hydrogen to produce 2 moles of ammonia.
Calculate the molar mass of
$\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ .
According to the balanced equation, 1 mole of
$\mathrm{BaCl}{}_{2}$ will react with 1 mole of
$\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ . Therefore, if
$0,0096\phantom{\rule{2pt}{0ex}}\mathrm{mol}$ of
$\mathrm{BaCl}{}_{2}$ react, then there must be the same number of moles of
$\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ that react because their mole ratio is 1:1.
According to the balanced equation, 2 moles of
$\mathrm{HCl}$ are produced for every 1 mole of the two reactants. Therefore the number of moles of
$\mathrm{HCl}$ produced is (
$2\times 0,0096$ ), which equals
$0,0096\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ .
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
$56\phantom{\rule{2pt}{0ex}}\mathrm{g}$ sample of iron sulphide (
$\mathrm{FeS}$ )
How many
moles of
$\mathrm{FeS}$ are there in the sample?
How many
molecules of
$\mathrm{FeS}$ 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.
More advanced calculations
Calculate the molar mass of the following chemical compounds:
$\mathrm{KOH}$
$\mathrm{FeCl}{}_{3}$
${\mathrm{Mg(OH)}}_{2}$
How many moles are present in:
$10\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of
$\mathrm{Na}{}_{2}$ SO
${}_{4}$
$34\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of
$\mathrm{Ca(OH)}{}_{2}$
$2,45\times 10{}^{23}$ molecules of
$\mathrm{CH}{}_{4}$ ?
For a sample of
$\mathrm{0,2}\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ of potassium bromide (
$\mathrm{KBr}$ ), calculate...
the number of moles of
${\mathrm{K}}^{+}$ ions
the number of moles of
${\mathrm{Br}}^{-}$ ions
You have a sample containing
$3\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ of calcium chloride.
What is the chemical formula of calcium chloride?
How many calcium atoms are in the sample?
Calculate the mass of:
$3\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ of
$\mathrm{NH}{}_{4}\mathrm{OH}$
$\mathrm{4,2}\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ of
$\mathrm{Ca}\left(\mathrm{NO}{}_{3}\right){}_{2}$
$\mathrm{96,2}\phantom{\rule{2pt}{0ex}}\mathrm{g}$ sulphur reacts with an unknown quantity of zinc according to the following equation:
$\mathrm{Zn}+\mathrm{S}\to \mathrm{ZnS}$
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:
${\mathrm{CaCl}}_{2}+{\mathrm{H}}_{2}{\mathrm{CO}}_{3}\to {\mathrm{CaCO}}_{3}+2\mathrm{HCl}$ If you want to produce
$10\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of calcium carbonate through this chemical reaction, what quantity (in g) of calcium chloride will you need at the start of the reaction?
Questions & Answers
how do you translate this in Algebraic Expressions
In this morden time nanotechnology used in many field .
1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc
2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc
3- Atomobile -MEMS, Coating on car etc.
and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change .
maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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The fundamental frequency of a sonometer wire streached by a load of relative density 's'are n¹ and n² when the load is in air and completly immersed in water respectively then the lation n²/na is