Question

For the following: i) SbH3 > AsH3 > PH3 > NH3 ii) Cl3CCOOH < CICH2COOH < Cl2CHCOOH < CH3COOH iii) H2O > H2S > H2Se > H2Te iv) HIO4 < HBrO4 < HCIO4 The order of acidity is correct for which series? O i, iii Oiii, iv Oi, iv O ii, iii O i, ii, iv

Answer 1

I)Option i is correct because,

SbH3>AsH3>PH3>NH3

The nitrogen atom is more electronegative means it has the strength to attract a bonding pair of electrons toward itself. The size of a central atom of nitrogen is smaller than other given compounds. Increase in electron density of NH3 will decreases the acidity.

SbH3 is the least base because the size of a central atom of SbH3 is much larger than nitrogen which increases its acidity.

ii)Cl3 C-COOH is more acidic than H3C-COOH due to the cumulative -Ieffect of three Cl atoms attached to C atom next to the COOH group.As a result of the -I effect (pulling of elctrons of bobd between Cl and Catom) of Cl atoms, C atom of COOH group develops +ve charge. To compensate the electron deficiency, the C atom of the COOH group, in turn, tends to pull the the shared electons pair between C and O atom of O-H group with more power than in H3C-COOH, thus giving more H+ ions in the aqueous solution.

Hence,Cl3C- COOH is more acidic than H3C-COOH.

So (ii) is wrong

iii) H2Te is the most acidic among the three. The sizes increase in the order S<Se<Te. Down the group, atomic size increases, and bond strength decreases. Hence, H2Te can release H-ion more easily than H2S, making it more acidic. This trend in acidity is observed all along the periodic table. Size of central atom is directly proportional to acidity of its hydride.

So this is(iii) wrong order given

iiii) Correct order

HClO4, perchloric acid, is the stronger acid.

In fact, perchloric acid is usually considered as the strongest of all simple acids.

Among oxoacids of elements of the same group having similar composition, acid strength increases as electronegativity increases. Since chlorine is more electronegative than bromine, HClO4 is a stronger acid than HBrO4.

There fore the final answer is 1 and 4