How much ethyl alcohol must be added to 1 litre of water so that the solution will freeze at -14° C ? ( K f . for water .=1.86° C / mol )

Question

How much ethyl alcohol must be added to 1 litre of water so that the solution will freeze at -14° C ? ( K f . for water .=1.86° C / mol ) (A) 7.5 mol (B) 8.5 mol (C) 9.5 mol (D) 10.5 mol

Tardigrade Admin · Accepted Answer

7.5 mol Δ Tf=Kf m Δ Tf=Kf (n2 × 1000/w1) 14=1.86 × (n2 × 1000/1000) n2=7.5 mol

Q. How much ethyl alcohol must be added to $1$ litre of water so that the solution will freeze at $- 1 4^{\circ} C$ ? $(K_{f}$ for water $= 1.8 6^{\circ} C / m o l)$

$7.5 m o l$

$8.5 m o l$

$9.5 m o l$

$10.5 m o l$

$7.5 m o l$
$Δ T_{f} = K_{f} m$
$Δ T_{f} = K_{f} \frac{n _{2} \times 1000}{w _{1}}$
$14 = 1.86 \times \frac{n _{2} \times 1000}{1000}$
$n_{2} = 7.5 m o l$

Q. How much ethyl alcohol must be added to 1 litre of water so that the solution will freeze at −14∘C ? (Kf​ for water =1.86∘C/mol)

7.5mol

8.5mol

9.5mol

10.5mol