# 0.9 Quantitative aspects of chemical change  (Page 4/10)

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Calculate the number of atoms there are in a sample of aluminium that weighs $80,94\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

1. $n=\frac{m}{M}=\frac{80,94}{26,98}=3\phantom{\rule{2pt}{0ex}}\mathrm{moles}$
2. Number of atoms in 3 mol aluminium $=3×6,022×10{}^{23}$

There are $18,069×10{}^{23}$ aluminium atoms in a sample of $80,94\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .

## Some simple calculations

1. Calculate the number of moles in each of the following samples:
1. $5,6\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of calcium
2. $0,02\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of manganese
3. $40\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of aluminium
2. A lead sinker has a mass of $5\phantom{\rule{2pt}{0ex}}\mathrm{g}$ .
1. Calculate the number of moles of lead the sinker contains.
2. How many lead atoms are in the sinker?
3. Calculate the mass of each of the following samples:
1. $2,5\phantom{\rule{2pt}{0ex}}\mathrm{mol}$ magnesium
2. $12\phantom{\rule{2pt}{0ex}}\mathrm{mol}$ lithium
3. $4,5×10{}^{25}$ 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 ( $\mathrm{HNO}{}_{3}$ ), it means you have $6,022×{10}^{23}$ molecules of nitric acid in the sample. This also means that there are $6,022×{10}^{23}$ atoms of hydrogen, $6,022×{10}^{23}$ atoms of nitrogen and ( $3×6,022×{10}^{23}$ ) 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 $\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ .

1. Hydrogen $=1,008\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ ; Sulphur = $=32,07\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ ; Oxygen $=16\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$

2. ${M}_{\left({H}_{2}S{O}_{4}\right)}=\left(2×1,008\right)+\left(32,07\right)+\left(4×16\right)=98,09\phantom{\rule{2pt}{0ex}}\mathrm{g}·{\mathrm{mol}}^{-1}$

Calculate the number of moles there are in $1\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ of $\mathrm{MgCl}{}_{2}$ .

1. $n=\frac{m}{M}$
1. Convert mass into grams
$m=1\mathrm{kg}×1 000=1 000\phantom{\rule{2pt}{0ex}}\mathrm{g}$
2. Calculate the molar mass of $\mathrm{MgCl}{}_{2}$ .
${M}_{\left({\mathrm{MgCl}}_{2}\right)}=24,31+\left(2×35,45\right)=95,21\phantom{\rule{2pt}{0ex}}\mathrm{g}·{\mathrm{mol}}^{-1}$
2. $n=\frac{1000}{95,21}=10,5\phantom{\rule{2pt}{0ex}}\mathrm{mol}$

There are $10,5\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ of magnesium chloride in a $1\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ sample.

Barium chloride and sulphuric acid react according to the following equation to produce barium sulphate and hydrochloric acid.

${\mathrm{BaCl}}_{2}+{\mathrm{H}}_{2}{\mathrm{SO}}_{4}\to {\mathrm{BaSO}}_{4}+2\mathrm{HCl}$

If you have $2\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of $\mathrm{BaCl}{}_{2}$ ...

1. What quantity (in g) of $\mathrm{H}{}_{2}\mathrm{SO}{}_{4}$ will you need for the reaction so that all the barium chloride is used up?
2. What mass of $\mathrm{HCl}$ is produced during the reaction?
1. $n=\frac{m}{M}=\frac{2}{208,24}=0,0096\phantom{\rule{2pt}{0ex}}\mathrm{mol}$
2. 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.

3. $m=n×M=0,0096×98,086=0,94\phantom{\rule{2pt}{0ex}}\mathrm{g}$

4. 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 ( $2×0,0096$ ), which equals $0,0096\phantom{\rule{2pt}{0ex}}\mathrm{moles}$ .

5. $m=n×M=0,0192×35,73=0,69\phantom{\rule{2pt}{0ex}}\mathrm{g}$

how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
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
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
how did you get the value of 2000N.What calculations are needed to arrive at it
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Good
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP