Class 11 Chemistry Notes GOC – Acidic Strength and Some Important Problems

Ex.1 Compare the acidic strength

1. HC1
2. HF
3. HBr
4. HI

Sol. Acidic strength ∝ stability of the anion formed (conjugate base)
As we know               I-> Br->Cl-> F
⇒H I >HBr>HCl> HF

Ex.2 Compare the Acidic strength of the following

1. NH3
2. PH3
3. AsH3
4. SbH3
5. BiH3

Sol. Anion formed from there acids are

Ex.3 Compare the acidic strength of the following compounds
CH4, NH3, H2O, HF
Sol. The conjugate base of the given acid is as follows

We have already proved that

⇒ HF > H2O > NH3>CH4 (acidic strength)

Ex.4. Compare the stability of the following carbanion.

Sol. b > c > b > a
* +M or –M is not distance dependent

Ex.5 Compare the stability of the following carbocation

Sol. a > b > c > d

Ex.6 Compare the stability of the following carbocation.

Sol. + M (OH) > + M (OCH3)
b > c > d > a

Ex.7 Compare the stability of the following carbocation

Sol.         c > a > b

Ex.8 Compare order of dehydration of the following alcohols:

1. 
2. 
3. C – C – C – OH

Sol. After formation of carbocation

Since 3o Carbocation is most stable therefore it will show greatest tendency to lose water as after lose of water it comes in stable form so the order of dehydration is a > b > c.

Acids and Bases

Ex.9 Compare the acidic strength of the following acids.

1. C – C – C – COOH
2. C = C – C – COOH
3. C ≡ C – C – COOH

Sol. The acid whose conjugate base is most stable will be more acidic.
After forming conjugate base from the above acids.

It is clear that sp hybridized carbon being most electronegative will decrease e- density from O most effectively making the conjugate base most stable.
c > b > a (acidic strength)

Vacant d-orbital available where C will coordinate its electron) (Pπ – dπbonding)
⇒ a <b (acidic strength)

Ex.11 Compare the acidic strength of the following

1. CHF3
2. CHCl3
3. CHBr3   (pπ – dπ bonding in Br is not as much as affective as in Cl due to large size of Br)

Sol. CHCl3> CHBr3> CHF3

Ex.12 Compare the acidic strength of the following

1. CH(CN)3
2. CH(NO2)3
3. CHCl3

After removing H+

More effective Resonance

b > a > c
* Negative charge on O is more
Stable than Negative charge on N as O is more electronegative than N.
* Pπ – Dπ Resonance < Actual Resonance

Ex.13 Compare the acidic strength of the following

1. CH ≡CH
2. CH2 = CH2
3. CH3 – CH3

Sol. 
(Stability of the conjugate base)
a > b > c(acidic strength)

Ex.14 Compare the acidic strength of the following:

1. CH3 – CH2 – CH2 – COOH
2. 
3. 
4. 

Sol. d > c > b > a

Ex.15 Compare the acidic strength of the following:

1. H2O
2. H2S
3. H2Se
4. H2Te

Sol. Conjugate base is in a stability order

Ex.1 6 Compare the acidic strength of the following compound

Sol After forming conjugate base of the above

c > d > b > a

Ex.17 Compare the reactivity of the following compounds with 1 mole of AgNO3

Sol. After removing Cl-

(Positive charge is not on resonance Least stable)

(Most stable as L.P. of Cl will be coordinated to positive charge completing the octet of each atom and making the corbocation most stable)

Extent of positive charge decreases stability increases

Ex.18 Compare the acidic strength

Sol. After making conjugate base

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