Question

The number of correct orders wrt the property mentioned along with is:

(i) HF > HCl > HBr > HI > (Boiling point) (ii) H2 S < H2Se < H2Te (Acidic strength) (iii) Cl2 > F2 (Bond energy) (iv) NH3 > PH3 > AsH3 > SbH3 (Proton affinity) (v) H3BO3 > H2CO3 (Acidic strength) (vi) HOCl > HClO3 (Acidic strength) (vii) H2O(s) < D2O(s) (Density) (viii) CH3CH2OH < CH3CHO < CH3COOH (Boiling point) (ix) H2O2 > H2O (Strength of H-bonding)

Answer 1

5

Answer 2

Let's evaluate each order:

(i) HF > HCl > HBr > HI (Boiling point)

Boiling point depends on molecular weight (van der Waals forces) and hydrogen bonding. HF exhibits strong hydrogen bonding. The boiling points are: HF (19.5 °C), HCl (-85.1 °C), HBr (-66.8 °C), HI (-35.4 °C). The correct order of decreasing boiling point is HF > HI > HBr > HCl. The given order is incorrect.

(ii) H2 S < H2Se < H2Te (Acidic strength)

Acidic strength of binary hydrides of Group 16 elements increases down the group as the bond strength decreases and the size of the central atom increases, making proton donation easier. The correct order is H2O < H2S < H2Se < H2Te. The given order H2 S < H2Se < H2Te is correct.

(iii) Cl2 > F2 (Bond energy)

The bond energy of halogens is expected to decrease down the group. However, F2 has an anomalously low bond energy due to significant lone pair-lone pair repulsion between the small F atoms. The bond energies are: F2 (159 kJ/mol), Cl2 (243 kJ/mol). The correct order is Cl2 > F2. The given order is correct.

(iv) NH3 > PH3 > AsH3 > SbH3 (Proton affinity)

Proton affinity is a measure of basicity. Basicity of Group 15 hydrides decreases down the group as the electron density on the central atom decreases due to increasing size and decreasing electronegativity. The correct order of basicity (proton affinity) is NH3 > PH3 > AsH3 > SbH3. The given order is correct.

(v) H3BO3 > H2CO3 (Acidic strength)

H3BO3 (Boric acid) is a weak monobasic Lewis acid (Ka ~ 10^-10). H2CO3 (Carbonic acid) is a weak diprotic Brønsted-Lowry acid (Ka1 ~ 4.3 x 10^-7). Since 10^-7 > 10^-10, H2CO3 is a stronger acid than H3BO3. The correct order is H2CO3 > H3BO3. The given order is incorrect.

(vi) HOCl > HClO3 (Acidic strength)

For oxoacids of the same central atom, acidic strength increases with the oxidation state of the central atom. In HOCl, the oxidation state of Cl is +1. In HClO3, the oxidation state of Cl is +5. Therefore, HClO3 is a stronger acid than HOCl. The correct order is HClO3 > HOCl. The given order is incorrect.

(vii) H2O(s) < D2O(s) (Density)

The density of ice (H2O(s)) at 0°C is 0.9167 g/cm³. The density of heavy ice (D2O(s)) at 0°C is 1.017 g/cm³. The density of solid heavy water is greater than the density of solid normal water. The given order H2O(s) < D2O(s) is correct.

(viii) CH3CH2OH < CH3CHO < CH3COOH (Boiling point)

Boiling point depends on intermolecular forces. Ethanol (CH3CH2OH) has hydrogen bonding. Ethanal (CH3CHO) has dipole-dipole forces. Ethanoic acid (CH3COOH) has strong hydrogen bonding (forms dimers). The boiling points are: Ethanal (20.2 °C), Ethanol (78.37 °C), Ethanoic acid (118 °C). The correct order of increasing boiling point is CH3CHO < CH3CH2OH < CH3COOH. The given order is incorrect.

(ix) H2O2 > H2O (Strength of H-bonding)

The boiling point of H2O2 (150.2 °C) is significantly higher than that of H2O (100 °C). This indicates stronger overall intermolecular forces in H2O2, which are dominated by hydrogen bonding. Therefore, the strength of hydrogen bonding (as reflected in boiling point) is considered greater in H2O2 than in H2O. The given order H2O2 > H2O is correct.

Counting the correct orders: (ii), (iii), (iv), (vii), (ix). There are 5 correct orders.

The final answer is $\boxed{5}$.