# DBT JRF 2020 — Question 98

Exam: DBT JRF 2020 · Section: B · Topic: Chemistry · Difficulty: Medium

## Question

The fluid property, due to which, mercury does not wet the glass is

## Options

- **A.** polarity
- **B.** viscosity
- **C.** specific gravity
- **D.** surface tension

## Answer

Option D

## Explanation

Mercury (Hg) is unique among metals in being liquid at room temperature (mp = $-38.8°C$ , bp = $356.7°C$ ). Its non-wetting of glass is due to SURFACE TENSION. Mercury has the highest surface tension of any common liquid ( $\approx 485 \text{ mN/m}$ at 20°C, compared to water = 72 mN/m). The cohesive forces between Hg atoms (metallic bonding/van der Waals) greatly exceed the adhesive forces between Hg and glass ( $\text{SiO}_2$ ). When placed on glass, Hg minimises surface area by beading up with a convex meniscus (contact angle $\approx 140°$ ), unlike water on glass (contact angle near 0°, concave meniscus). High surface tension also means Hg in a capillary tube shows depression (not elevation as water does).

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