# 15.1 Stoichiometry and composition  (Page 2/5)

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$207\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of lead combines with oxygen to form $239\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of a lead oxide. Use this information to work out the formula of the lead oxide (Relative atomic masses: $\mathrm{Pb}=207\phantom{\rule{2pt}{0ex}}\mathrm{u}$ and $\mathrm{O}=16\phantom{\rule{2pt}{0ex}}\mathrm{u}$ ).

1. $239-207=32\phantom{\rule{2pt}{0ex}}\mathrm{g}$
2. $n=\frac{m}{M}$

$\frac{207}{207}=1\phantom{\rule{2pt}{0ex}}\mathrm{mol}$

Oxygen

$\frac{32}{16}=2\phantom{\rule{2pt}{0ex}}\mathrm{mol}$
3. The mole ratio of $\mathrm{Pb}:\mathrm{O}$ in the product is 1:2, which means that for every atom of lead, there will be two atoms of oxygen. The formula of the compound is $\mathrm{PbO}{}_{2}$ .

Vinegar, which is used in our homes, is a dilute form of acetic acid. A sample of acetic acid has the following percentage composition: 39,9% carbon, 6,7% hyrogen and 53,4% oxygen.

1. Determine the empirical formula of acetic acid.
2. Determine the molecular formula of acetic acid if the molar mass of acetic acid is $60\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ .
1. In $100\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of acetic acid, there is $39,9\phantom{\rule{2pt}{0ex}}\mathrm{g}\phantom{\rule{2pt}{0ex}}\mathrm{C}$ , $6,7\phantom{\rule{2pt}{0ex}}\mathrm{g}\phantom{\rule{2pt}{0ex}}\mathrm{H}$ and $53,4\phantom{\rule{2pt}{0ex}}\mathrm{g}\phantom{\rule{2pt}{0ex}}\mathrm{O}$

2. $n=\frac{m}{M}$

$\begin{array}{ccc}\hfill {n}_{C}& =& \frac{39,9}{12}=3,33\phantom{\rule{2pt}{0ex}}\mathrm{mol}\hfill \\ \hfill {n}_{H}& =& \frac{6,7}{1}=6,7\phantom{\rule{2pt}{0ex}}\mathrm{mol}\hfill \\ \hfill {n}_{O}& =& \frac{53,4}{16}=3,34\phantom{\rule{2pt}{0ex}}\mathrm{mol}\hfill \end{array}$
3. Empirical formula is $\mathrm{CH}{}_{2}\mathrm{O}$

4. The molar mass of acetic acid using the empirical formula is $30\phantom{\rule{2pt}{0ex}}\mathrm{g}·\mathrm{mol}{}^{-1}$ . Therefore the actual number of moles of each element must be double what it is in the empirical formula.

The molecular formula is therefore $\mathrm{C}{}_{2}\mathrm{H}{}_{4}\mathrm{O}{}_{2}$ or $\mathrm{CH}{}_{3}\mathrm{COOH}$

Aluminium trichloride ( ${\mathrm{AlCl}}_{3}$ ) is an ionic substance that forms crystals in the solid phase. Water molecules may be trapped inside the crystal lattice. We represent this as: ${\mathrm{AlCl}}_{3}·n{\mathrm{H}}_{2}\mathrm{O}$ . A learner heated some aluminium trichloride crystals until all the water had evaporated and found that the mass after heating was $2,8\phantom{\rule{2pt}{0ex}}\mathrm{g}$ . The mass before heating was $5\phantom{\rule{2pt}{0ex}}\mathrm{g}$ . What is the number of moles of water molecules in the aluminium trichloride?

1. We first need to find n, the number of water molecules that are present in the crystal. To do this we first note that the mass of water lost is $5-2,8=2,2$ .

2. The next step is to work out the mass ratio of aluminium trichloride to water and the mole ratio. The mass ratio is:

$2,8:2,2$
To work out the mole ratio we divide the mass ratio by the molecular mass of each species:
$\frac{2,8}{133}:\frac{2,2}{18}=0,021:0,12$
Next we do the following:
$0,021\frac{1}{0,021}=1$
and
$\frac{0,12}{0,021}=6$
So the mole ratio of aluminium trichloride to water is:
$1:6$

3. And now we know that there are 6 moles of water molecules in the crystal.

## Moles and empirical formulae

1. Calcium chloride is produced as the product of a chemical reaction.
1. What is the formula of calcium chloride?
2. What percentage does each of the elements contribute to the mass of a molecule of calcium chloride?
3. If the sample contains $5\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of calcium chloride, what is the mass of calcium in the sample?
4. How many moles of calcium chloride are in the sample?
2. $13\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of zinc combines with $6,4\phantom{\rule{2pt}{0ex}}\mathrm{g}$ of sulphur. What is the empirical formula of zinc sulphide?
1. What mass of zinc sulphide will be produced?
2. What percentage does each of the elements in zinc sulphide contribute to its mass?
3. Determine the formula of zinc sulphide.
3. A calcium mineral consisted of 29,4% calcium, 23,5% sulphur and 47,1% oxygen by mass. Calculate the empirical formula of the mineral.
4. A chlorinated hydrocarbon compound was analysed and found to consist of 24,24% carbon, 4,04% hydrogen and 71,72% chlorine. From another experiment the molecular mass was found to be $99\mathrm{g}·\mathrm{mol}{}^{-1}$ . Deduce the empirical and molecular formula.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
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
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
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
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
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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
Properties of longitudinal waves