urgent help need in chemistry please SAVE ME!!!!!

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Qer
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#1
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hi
i am stuck on these some questions need help

Which of these substances has permanent dipole-dipole attractions between
molecules?
[1 mark]
A CCl4
B C2F4
C (CH3)2CO
D CO2
Which of these samples of gas contains the largest number of molecules?
The gas constant R = 8.31 J K–1 mol–1
.
[1 mark]
A 5.0 × 10–4m3 at 1.0 × 106 Pa and 300 K
B 4.0 × 10–3m3 at 2.0 × 105 Pa and 400 K
C 3.0 × 101 dm3 at 3.0 × 104 Pa and 500 K
D 2.0 × 102 dm3 at 4.0 × 103 Pa and 600 K


please give me explanation also
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Rexx18
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(Original post by Qer)
hi
i am stuck on these some questions need help

Which of these substances has permanent dipole-dipole attractions between
molecules?
[1 mark]
A CCl4
B C2F4
C (CH3)2CO
D CO2
Which of these samples of gas contains the largest number of molecules?
The gas constant R = 8.31 J K–1 mol–1
.
[1 mark]
A 5.0 × 10–4m3 at 1.0 × 106 Pa and 300 K
B 4.0 × 10–3m3 at 2.0 × 105 Pa and 400 K
C 3.0 × 101 dm3 at 3.0 × 104 Pa and 500 K
D 2.0 × 102 dm3 at 4.0 × 103 Pa and 600 K


please give me explanation also
CCl4 can't be polar since all polar bonds cancel out.
C2F4 can't be polar for the same reason.
(CH3)2CO is polar due to the C=O bond.
CO2 can't be polar because it's linear and the polarities cancel out.

For the second part, use pV = nRT to find the number of moles of each one. The one with the most moles contains most molecules (you can multiply each mole by Avogadro's but you don't have to since all would be multiplied by the same constant so it makes no difference).
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Qer
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(Original post by Rexx18)
CCl4 can't be polar since all polar bonds cancel out.
C2F4 can't be polar for the same reason.
(CH3)2CO is polar due to the C=O bond.
CO2 can't be polar because it's linear and the polarities cancel out.

For the second part, use pV = nRT to find the number of moles of each one. The one with the most moles contains most molecules (you can multiply each mole by Avogadro's but you don't have to since all would be multiplied by the same constant so it makes no difference).
(CH3)2CO is polar due to the C=O bond.
CAN U PLEASE EXPLAIN THIS
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Rexx18
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(Original post by Qer)
(CH3)2CO is polar due to the C=O bond.
CAN U PLEASE EXPLAIN THIS
C=O is an example of a polar bond. Oxygen is significantly more electronegative than carbon, therefore it will draw the bonding pair of electrons towards itself in the covalent bond. This induces a delta (slight) positive charge on the carbon and a delta negative charge on the oxygen. This means there will be electrostatic (between something positive and negative) attraction between a delta + H on one molecule and a delta - O on a neighbouring molecule. These are known as permanent dipole-dipole forces.

If you were to draw the molecule out, it would be propanone, a C=O and a CH3 group either side of the carbon.
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Qer
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#5
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#5
In every bond ( except co2) c=o present have permanent dipole forces?
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Rexx18
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(Original post by Qer)
In every bond ( except co2) c=o present have permanent dipole forces?
Always draw out the molecule with its correct shape and see if there's a line of symmetry. If there is one and the polar bonds are facing away from each other, then they will cancel out and the molecule is non-polar.

Molecules containing C=O bonds (mainly aldehydes or ketones) are almost always polar and will display permanent dipole-dipole forces.
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Qer
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Just want to clear
Line of symmetry means
Draw a molecule and draw line in middle if both sides are identical so they are non polar???
Is this right?
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Rexx18
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(Original post by Qer)
Just want to clear
Line of symmetry means
Draw a molecule and draw line in middle if both sides are identical so they are non polar???
Is this right?
Yes, if something is symmetrical and you draw a line down the middle of it, then the 2 halves will be mirror images and the polarities will cancel out.
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Qer
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Thanks for all help
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