Sir/madam I have a question. How can we say that water spreads on glass easily inspite of its low surface tension. Also how can we say that the interface of mercury-glass does not spread on glass easily inspite of its high surface tension?????plz reply quickly!!!

Asked by shravan s | 2nd Dec, 2013, 11:48: AM

Expert Answer:

How easily a liquid drop spreads on a solid surface depends on contact angle.
 
A contact angle less than 90° (low contact angle) usually indicates that wetting of the surface is very favorable, and the fluid will spread over a large area of the surface. Contact angles greater than 90° (high contact angle) generally means that wetting of the surface is unfavorable so the fluid will minimize contact with the surface and form a compact liquid droplet.
The angle of contact between water and glass typically lies in the range to , whereas that between mercury and glass is about
Therefore, mercury does not spread easily on glass surface while water spreads easily on it.
 

Contact angle

Degree of wetting

θ = 0

Perfect wetting

0 < θ < 90°

high wettability

90° ≤ θ < 180°

low wettability

θ = 180°

perfectly
non-wetting

Answered by Komal Parmar | 2nd Dec, 2013, 03:02: PM

Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day.