# Help with limiting reagent and bond polarity

Watch
Announcements
#1
order the molecules in order of increasing polarity
CF4
CHCl2F
CH2Br2
CH3I

CF4
CH3I
CH2Br2
CHCl2F
0
#2
Can you also explain a method to work out the limiting reagent
0
5 years ago
#3
(Original post by Loyale)
order the molecules in order of increasing polarity
CF4
CHCl2F
CH2Br2
CH3I

CF4
CH3I
CH2Br2
CHCl2F
Which ones don't you understand from that ordering?
0
#4
(Original post by langlitz)
Which ones don't you understand from that ordering?

I dont understand how to come to the answer and how to order them
0
5 years ago
#5
(Original post by Loyale)
Can you also explain a method to work out the limiting reagent
Work out the number of moles of each reactant present. Then find the ratio in which the reactants react to form the product.

e.g.

So if you had 3 moles of HCl and 1 mole of CaCO3 what's he limiting reagent?
Spoiler:
Show
the limiting reagent would be CaCO3 because you there would be 1 mol of HCl left unreacted. HCl reacts with CaCO3 in a 2:1 ratio so the 3 mol of HCl would need 1.5 mol of CaCO3 to react completely
0
5 years ago
#6
(Original post by Loyale)
I dont understand how to come to the answer and how to order them
Ok I'll try an explain it

So the electronegativity values are F > Cl > Br > I (electronegativity increases up and across from left to right on the periodic table, this is something you should learn as it will come in very useful). CF4 is non-polar because, although F has the highest electronegativity of any element, they are equally spaced around the carbon. So the pull on it's electrons cancel each other out.

The other ones are fairly intuitive. Increasing the number of electronegative elements will increase the polarity of the molecule.
1
5 years ago
#7
Electronegativity increases across a period and decreases down a group
CF4 is non polar because the 4 F atoms are equally spaced around the central C atom and so the dipoles cancel.
For the remaining 3 molecules we need to use Pauling's electronegativity values (you can google this if you are unsure of what it is - it's basically just the periodic table but the electronegativity values)
All you have to do is work out the difference between the most electronegative atom in the molecule (the one with the highest value) and the least electronegative atom in the molecule (the one with the lowest value)
By doing this we roughly get the values:
CH3I = 0.46
CH2Br2 = 0.76
CHClF = 1.8
...putting them in that order.

Polarity just how polar a molecule is. So the higher the electronegativity difference the more polar the molecule is.

As for the limiting reagent, it is just the one that is completely used up first in a reaction
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### What support do you need with your UCAS application?

I need help researching unis (7)
11.48%
I need help researching courses (5)
8.2%
I need help with filling out the application form (3)
4.92%
I need help with my personal statement (26)
42.62%
I need help with understanding how to make my application stand out (15)
24.59%
I need help with something else (let us know in the thread!) (2)
3.28%
I'm feeling confident about my application and don't need any help at the moment (3)
4.92%