# 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.

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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Good
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