Edexcel CHEMISTRY DOUBTS!!!!

[raimunts]

hello. are polar and non-polar molecules in Unit 1 syllabus? Can someone please briefly explain them if they are.

[Kim]

hello. are polar and non-polar molecules in Unit 1 syllabus? Can someone please briefly explain them if they are.

well they are not there
polar molecule- is a molecule where the bonded electrons are shared unequally.the bonded atoms are different wid different electronegativities
non polar-is a molecule where the bonded electrons are shared equally.bonded atoms are the same wid same electronegativities
 all assymetrical molecules are polar
in symmetrical molecules the dipoles cancel each other out so the molecule is non polar

[raimunts]

Polarity has got something to do with why compounds with low electronegatitvity behave like covalent compounds even though they are ionic?

[Kim]

yes

[raimunts]

6CH01, JAN 2009, Q. 23 (bi)
While applying Hess's law, why is H1= 2*H2 - H3 [why is H2 multiplied by 2?]

[Kim]

6CH01, JAN 2009, Q. 23 (bi)
While applying Hess's law, why is H1= 2*H2 - H3 [why is H2 multiplied by 2?]

because there are 2 moles of KHCO3

[raimunts]

because there are 2 moles of KHCO3

thanx! uv answered about 6 questions of mine just tonight [and prolly many more to come]...i owe my chemistry A (hopefully A) to this site nd u ppl!

[raimunts]

17 Which of the following gas samples occupies the greatest volume at the same
   temperature and pressure?
   [Relative atomic masses: H = 1; C = 12; O = 16; F = 19; Ne = 20]
      A    1 gram of ethane
      B    1 gram of oxygen
      C    1 gram of fluorine
      D    1 gram of neon

Answer in mark scheme is D. Neon. Isn't Number of moles = Mass/Molar mass, and more moles mean greater volume, so shouldnt Oxygen having least Molar mass occupy greatest volume>

[raimunts]

Oh no need. I got it. Oxygen and Fluorine are diatomic. So neon is ryt.

[Meticulous]

First you have to calculate number of moles.

mol= mass/Ar...and take care Ar of oxygen is 32, not 16.

then multiply the mole by 24 dm³

[Meticulous]

Ooops. Didnt see your last post.

[raimunts]

2 Chlorine has two isotopes with relative isotopic mass 35 and 37. Four m/z values are
  given below. Which will occur in a mass spectrum of chlorine gas, Cl2, from an ion
  with a single positive charge?
       A    35.5
       B    36
       C    71
       D    72

Any idea?

[raimunts]

3 The human body contains around 0.025 g of iodine molecules, I2. Which of the
  following shows the number of iodine atoms in 0.025 g of I2?
  The Avogadro constant is 6.02 × 1023 mol–1.
             0.025
                   × 6.02 × 1023
        A
             126.9
             0.025
                   × 6.02 × 1023
        B
             253.8
             253.8
                   × 6.02 × 1023
        C
             0.025
             126.9
                   × 6.02 × 1023
        D
             0.025

6PH01. Jan 2010 Q.2 and Q.3. The mark scheme answers seem weird

[Meticulous]

first you find the number of moles:

mass/mr of iodine molecules,

the multiply by 2 because there are 2 iodine atoms in each mole.

the 2 cancels out with the Mr.

[Uchia]

and for your previous question

the possible peaks on the mass spectrometer would be (Cl35 Cl35)+, (Cl37 Cl37)+, (Cl35 Cl37)+     well calculate the mr and see which one is given

35+35 = 70
37+37 =74
35 + 37 =72

so 72 is the right answer