Chemistry 2006

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Chemistry 2006

• Session1

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• Any questions??
• For these sessions to really work, you need to be
  prepared and HONEST.
• I want you to leave HOPING you get questions like
  we are doing tonight
• You should be 100 confident with this content
• So get it sorted. Ask NOW

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Empirical formula calculation

• A compound was found to contain 0.4248g Carbon,
  0.1062g Hydrogen 0.285g Oxygen.
• What is the empirical formula

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Did you get it?

• C2H6O

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Taking it further

• A hydrocabon, with a relative molecular mass of
  56 was found to contain 0.12g of carbon and 0.02g
  of hydrogen.
• What is the empirical formula?
• What is the molecular formula?
• Name a possible compound with this molecular
  formula

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The answers

• Empirical formula is CH2
• Molecular formula is C4H8
• Compounds could be butene or cyclobutane

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Nuclear equations

• Complete the following equations
• 216 84Po ? ____ 42a
• The decay of 3215P by beta emission
• What will I be left with after 23892U has
  undergone an alpha decay, followed by a beta
  decay and finally another alpha decay?

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Answers

• A) 21282Pb
• B) 3216S 0-1ß
• C) 23089Ac
• Next- Define the term isotope

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A question about isotopes

• A mass spectrum provides data about the relative
  abundance of 3 isotopes of magnesium. Calculate
  the relative atomic mass of magnesium to two
  decimal places
• m/z value of peak abundance
• 24 78.6
• 25 10.1
• 26 11.3

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Did you get it?

• 24.33!
• (24 x 78.6 25 x 10.1 26 x 11.3)/100

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• The half life of iodine-235 is 6.5 hours. How
  long will it take for a 100g sample to decay to
  12.5g?
• Strontium-90 has a half-life of 28 years. What
  will be left after 84 years?

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• 1) 19.5 hours- 3 half lifes!!
• 2) 12.5 - 3 half lifes!!
• Why is the knowledge of a half life of any
  isotope with a medical application essential to
  its application?
• Name a use for a radioactive tracer

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• Define the term relative atomic mass
• Give the symbol, including mass number and proton
  number, for the isotope which has a mass number
  of 34 and which has 18 neutrons in each nucleus

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Still going strong?

• Now complete the past paper question provided.
• More next week! You need to write your revision
  notes for the rest of EL- and Ill provide more
  brain teasers next week- with no guarantee I
  wont revisit some of todays topics- so be
  ready.
• Finally if you have any suggestions or comments
  (good or bad) let me know- its for your benefit
  after all!