Empirical Formulae From Percentage Composition | Chemical Calculations | Chemistry | FuseSchool

00:04:33
https://www.youtube.com/watch?v=5xVTw6LFG2E

Summary

TLDRThis video lesson covers the difference between empirical and molecular formulas and teaches how to derive them. The molecular formula of a compound indicates the types of atoms present and their exact count, while the empirical formula provides the simplest ratio of these atoms. An example with a compound of nitrogen and hydrogen is used, where the molecular formula is N2H4 and the empirical formula is NH2. The process involves calculating from percentage composition by mass: dividing the percentages by atomic masses, finding the simplest ratio, and using the empirical formula to find the molecular formula by factoring in the molecular mass.

Takeaways

  • 🔍 Empirical formula shows simplest ratio of atoms.
  • 🧪 Molecular formula gives exact number of atoms.
  • 📊 Use percentage composition to find empirical formula.
  • 🔢 Ratio simplification is key in empirical formula.
  • 🔀 Empirical to molecular formula conversion involves molecular mass.
  • 📉 Nitrogen and hydrogen example illustrates concept.
  • 📏 Empirical mass helps find the molecular formula.
  • 💡 Understand atomic composition through formulas.
  • 🔬 Chemistry formulas reveal elemental structure.
  • 🧮 Calculate elements' ratios accurately.

Timeline

  • 00:00:00 - 00:04:33

    This video covers the differences between empirical and molecular formulas and guides on how to derive them from percentage composition. Using hydrazine (N2H4) as an example, it explains that the molecular formula indicates both the types and the exact number of atoms present, while the empirical formula shows the types and the simplest ratio of those atoms. For empirical formulas derived from mass percentages, the method involves calculating the ratio of atoms by dividing percentage over atomic mass and simplifying results. In contrast, deriving the molecular formula involves multiplying the empirical formula by a whole number determined by dividing molecular mass by empirical mass, exemplified through computations.

Mind Map

Video Q&A

  • What is the difference between the molecular formula and empirical formula?

    The molecular formula indicates the types and exact number of each atom in a compound, while the empirical formula shows the simplest ratio of the elements.

  • How do you calculate the empirical formula from percentage composition by mass?

    First, list the elements with their respective percentage compositions. Then divide each by its atomic mass and find the simplest ratio.

  • How is the molecular formula derived from the empirical formula?

    The molecular formula is the empirical formula multiplied by a whole number (n), determined by dividing the molecular mass by the empirical mass.

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  • 00:00:10
    [Music]
  • 00:00:14
    in this video you're going to learn the
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    difference between empirical formula and
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    molecular formula how to find the
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    empirical formula from percentage
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    composition by mass and how to find
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    molecular formula from the empirical
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    formula consider the compound hydren its
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    molecular formula is
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    n2h4 but its empirical formula is
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    nh2 the molecular formula of a compound
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    tells us two things one the types of
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    atom in the molecule in this case
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    nitrogen and hydrogen and two how many
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    types of each atom in this case there
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    are two nitrogen atoms and four hydrogen
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    atoms the EMP empirical formula of a
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    compound also tells us two things one
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    the types of atoms in the molecule in
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    this case nitrogen and hydrogen and two
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    the simplest ratio of each type of atom
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    the ratio of nitrogen to hydrogen in
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    hydrogene is 2: 4 making the simplest
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    ratio
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    1:2 the best way to find the empirical
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    formula from percentage composition by
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    mass is to go over a question upon
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    analysis the percentage composition by
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    mass of a compound was found to be
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    87.5% nitrogen and 12.5% hydrogen now
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    calculate the empirical formula firstly
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    we have a column for each element n for
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    nitrogen and H for hydrogen then under
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    each element we put the percentage
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    composition by mass so that's
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    87.5% for nitrogen and 12 .5% for
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    hydrogen we then divide these
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    percentages by the relative atomic mass
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    of each element so that's 14 for
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    nitrogen and one for hydrogen doing this
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    calculation gives us
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    6.25 for nitrogen and 12.5 for hydrogen
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    we then divide these numbers by the
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    smallest of the two which is
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    6.25 and this gives us the ratio of 1 to
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    2 1 and two is the smallest possible
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    ratio so the empirical formula is n H2
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    but how do we find the molecular formula
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    the molecular mass for this compound is
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    32 the molecular formula is the
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    empirical formula time n where n is the
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    number by which we have to multiply the
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    empirical formula in order to get the
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    molecular formula I have coined the
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    phrase empirical Mass to describe the
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    mass of the empirical formula so in this
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    case we have nitrogen which is 14 plus
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    hydrogen which is 2 giving us 16 now
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    just as the molecular formula is the
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    empirical formula time n the molecular
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    mass is the empirical mass time n so
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    molecular mass of 32 is n * the
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    empirical Mass 16
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    therefore n is 32 / 16 or 2 so now
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    molecular formula is the empirical
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    formula time n so that's nh2 * n or nh2
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    * 2 which gives us N2
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    H4 so to recap the mular formula tells
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    us the types of atoms in a molecule and
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    their exact number and the empirical
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    formula tells us the types of atoms in
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    the molecule and their simplest
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    ratio
Tags
  • Empirical Formula
  • Molecular Formula
  • Chemistry
  • Percentage Composition
  • Atomic Mass