Ncert Solutions Chemistry Class 11th

1.14. S.I. unit of mass is kilogram (kg).

It is defined as the mass of platinum-iridium block stored at international bureau of weights and measures in France.

(a) Neutral — CO
Acidic — B₂O₃, SiO₂, CO₂ 

Basic — Tl₂O₃ 

Amphoteric — Al₂O₃, PbO₂

(b)-CO does not react with acid as well as base at room temperature.
Being acidic B₂O₃, SiO₂ and CO₂ react with alkalis to form salts.

B₂O₃ + 2NaOH à 2NaBO₂ + H₂O

SiO₂ + NaOH à 2Na₂SiO₃ + H₂O

CO₂ + 2NaOH à Na₂CO₃ + H₂O

Being Amphoteric, Al₂O₃, PbO₂ react with acids and bases.

Al₂O₃ + 2NaOH à 2NaAlO₂ + H₂O

Al₂O₃ + 3H₂SO₄à (Al₂SO₄)₃+ 3H₂O

PbO₂ + 2 NaOH à Na₂PbO₃ + H₂O

2PbO₂ + 2 H₂SO₄à 2PbSO₄ + 2H₂O + O₂

Being basic Tl₂O₃ dissolves in acids

Tl₂O₃ + 6HCl à 2TlCl₃ + 3H₂O

1.13. Pressure= Force/Area

But weight = m x g, where m = mass (in kg) and g = 9.8 m/s²

Therefore, Pressure = 1034 g cm^-2 x 9.8 m/s²

= 1034 x 10^-3 kg x (100 m)² x 9.8 m/s²

= 101332 Pa

= 1.01332 x 10⁵ Pa

1.12. Density of methanol = 0.793 kg/L, molar mass of methanol (CH₃OH) = 32g/mol = 0.032 kg/mol

V₁ =? , V₂ = 2.5 L, M₂ = 0.25 M

We can apply the formula of

M₁V₁ = M₂V₂

Or V₁ = M₂V₂/M₁

Substituting M₁ = density / molar mass, we get

M₁ = 0.793/0.032 = 24.78

V₁ = 0.25 x 2.5 / 24.78 = 0.02522 L = 25.22 mL

1.11. Molar mass of sugar = (12 x 12) + (22 x 1) + (11 x 16) =342 g/mol

No. of moles in 352 g of sugar = 1 mol

No. of moles in 20 g = 20 x 1/352 = 0.0585 mol

Therefore, molar concentration = moles of solute / volume of solution in L = 0.0585 / 2 = 0.0293 mol/L

Due to poor shielding effect of d-electrons in Ga, the electrons in gallium experience great force of attraction by nucleus as compared to Al. That is why Ga has lower atomic radius as compared to Al.

Because there is increase in atomic size on moving from carbon to silicon, the screening effect increases. Thus, the force of attraction of nucleus for the valence electron in silicon decreases as compared to carbon. Therefore, the ionization enthalpy decreases from carbon to silicon.

1.10. (i) 1 mole of C₂H₆ contains 2 moles of carbon atoms

     Therefore, no of moles of C atoms in 3 moles of C₂H₆ = 6 moles
(ii) 1 mole of C₂H₆ contains 6 moles of hydrogen atoms
      Therefore, no of moles of  H atoms in 3 moles of C₂H₆ = 18 moles

(iii) 1 mole of C₂H₆ contains 6.02 x 10²³ molecules

      Therefore, 3 moles of C₂H₆ will contain ethane molecules = 3 x 6.02 x 10²³ molecules= 18.06 x 10²³ molecules