Answer:
<em>C</em> C2H5OH = 7.598 molal
Explanation:
- molality (m) C2H5OH = n C2H5OH / Kg H2O
∴ V C2H5OH = 50.0 mL
∴ V H2O = 112.7 mL
∴ T = 20 °C
∴ δ C2H5OH (20°C) = 0.789 g/mL
∴ δ H2O (20°C) = 1.00 g/mL
∴ Mw C2H5OH = 46.0684 g/mol
⇒ n C2H5OH = (50.0 mL)×(0.789 g/mL)×(mol/46.0684 g) = 0.8563 mol
⇒ mass H2O = (112.7 mL)×(1.00 g/mL)×(Kg / 1000 g) = 0.1127 Kg
⇒ <em>C</em> C2H5OH = 0.8563 mol C2H5OH / 0.1127 Kg H2O
⇒ <em>C</em> C2H5OH = 7.598 molal
The answer is surface tension. The water has an inward attraction because there are no molecules above it (I mean water, at least), and the legs of water bugs repel water, hence, they walk on water.
Hope this helps!