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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

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
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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