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207 g of lead combines with oxygen to form 239 g of a lead oxide. Use this information to work out the formula of the lead oxide (Relative atomic masses: Pb = 207 u and O = 16 u ).

  1. 239 - 207 = 32 g
  2. n = m M


    207 207 = 1 mol


    32 16 = 2 mol
  3. The mole ratio of Pb : 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 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 g · mol - 1 .
  1. In 100 g of acetic acid, there is 39,9 g C , 6,7 g H and 53,4 g O

  2. n = m M

    n C = 39 , 9 12 = 3 , 33 mol n H = 6 , 7 1 = 6 , 7 mol n O = 53 , 4 16 = 3 , 34 mol
  3. Empirical formula is CH 2 O

  4. The molar mass of acetic acid using the empirical formula is 30 g · 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 C 2 H 4 O 2 or CH 3 COOH

Aluminium trichloride ( 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: AlCl 3 · n H 2 O . A learner heated some aluminium trichloride crystals until all the water had evaporated and found that the mass after heating was 2,8 g . The mass before heating was 5 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:
    2,8 133 : 2,2 18 = 0,021 : 0,12
    Next we do the following:
    0,021 1 0,021 = 1
    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.

Khan academy video on molecular and empirical formulae - 1

Khan academy video on mass composition - 1

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 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 g of zinc combines with 6,4 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 g · mol - 1 . Deduce the empirical and molecular formula.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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
Mukesh Reply
Properties of longitudinal waves
Sharoon Reply

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Source:  OpenStax, Siyavula textbooks: grade 10 physical science [caps]. OpenStax CNX. Sep 30, 2011 Download for free at http://cnx.org/content/col11305/1.7
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