Mercury convex meniscus

Why does water form a concave meniscus in a tube, while mercury forms a convex meniscus ... 

Mercury forms a convex meniscus with glass rather than the concave meniscus shown in Figure 8.18. What does this tell you about the cohesive forces between mercury atoms versus the adhesive forces between mercury atoms and glass Which forces are stronger ... 

How to Measure a Liquid. If you look through the side of a measuring glass filled with a liquid, you will see that the surface of the liquid has a double curve. This curve is called the meniscus. In measuring, be sure to use the lowest part of the lower.curve. Most liquids have a concave meniscus (one that curves downward) but very dense liquids like mercury have a convex meniscus (one that curves upward). In that case, use the uppermost part of the upper curve for measuring. 

A convex meniscus occurs in a liquid in which the cohesive forces are greater than the adhesive forces (an example is mercury in a glass tube). 

Water forms a concave meniscus, whereas mercury produces a convex meniscus. In the case of mercury, there is essentially no attractive force between the mercury atoms and the silicon dioxide to compete with the attractive forces between the mercury atoms themselves. The mercury forms a convex (high-centered) meniscus because the only force Is the Interparticle attractive force between mercury atoms, which produces surface tension. 

When mercury is placed in a glass cylinder, it forms a convex meniscus. Why does it do so ... 

The curvature of the interface depends on the relative magnitudes of the adhesive forces between the liquid and the capillary wall and the internal cohesive forces in the liquid. When the adhesive forces exceed the cohesive forces, 9 lies in the range 0° < 9 < 90° when the cohesive forces exceed the adhesive forces, 90° < 9 < 180°. When 9 > 90°, the cos 9 term is negative, resulting in a convex meniscus towards the vapor phase and the liquid level in the capillary falling below the liquid level in the container (capillary depression). This occurs with liquid mercury in glass where 9 = 140° and also with water in capillary tubes coated internally with paraffin wax. Thus, liquid mercury is used in the evaluation of the porosity of solid adsorbents in the mercury injection porosimetry technique (see Section 8.5). 

Figure 12.19 Shape of water or mercury meniscus in glass. A, Water displays a concave meniscus in a glass tube because the adhesive (H-bond) forces between the H2O molecules and the O—Si—O groups of the glass are stronger than the cohesive (H-bond) forces within the water. B, Mercury displays a convex meniscus in a glass tube because the cohesive (metallic bonding) forces within the mercury are stronger than the adhesive (dispersion) forces between the mercury and the glass.

Nonpolar liquid mercury forms a convex meniscus in a glass tube, whereas polar water forms a concave meniscus. 

The meniscus in liquids is further evidence of cohesive and adhesive forces. When a liquid is placed in a glass cylinder, the surface of the liquid shows a curve called the meniscus (see Figure 13.5). The concave shape of water s meniscus shows that the adhesive forces between the glass and water are stronger than the cohesive forces within the water. In a nonpolar substance such as mercury, the meniscus is convex, indicating that the cohesive forces within mercury are greater than the adhesive forces between the glass wall and the mercury. 

Figure 13-9 The meniscus, as observed in glass tubes (a) with water (concave) and (b) with mercury (convex).

A FIGURE 11.22 Meniscuses of Water and Mercury The meniscus of water is concave because water molecules are more strongly attracted to the glass wall than to one another. The meniscus of mercury is convex because mercury atoms are more strongly attracted to one another than to the glass walls. 

It is these kinds of uncertainties that have led to the development of mercury porosimetry, in which, since the meniscus is convex, the mercury has to be forced into the pores under pressure. Mercury porosimetry is the subject of Section 3.9. 

MENISCUS. The curved siirlaee or a liquid, particularly noticeable in vessels ol tubes of small diameter and due in the surface tension of the liquid. If the liquid wets the containing vessel, the meniscus is concave otherwise it is convex. The meniscus of mercury in glass is convex. 

FIGURE 11.10 (a) When adhesion is greater than cohesion, the liquid (for example, water) rises in the capillary tube, (b) When cohesion is greater than adhesion, as it is for mercury, a depression of the liquid in the capillary tube results. Note that the meniscus in the tube of water is concave, or rounded downward, whereas that in the tube of mercury is convex, or rounded upward. 

Mercury is an ideal fluid for porosimetry because it is non-wetting and has a high surface tension. Surface tension is responsible for the shape that liquid droplets form on surfaces as well as their maximum size. The units are force per unit length or energy per unit area. The meniscus of water in a capillary mbe is concave while it is convex for mercury. However, in a copper tube, the meniscus for both water and mercury is concave. Because of the adhesion between the wall of the capillary and the liquid, the liquid may be drawn up to a height h. The height depends on the liquid-air surface tension, yia, the contact angle, 0, the density of the fluid, p, and the radius of the capillary, r ... 

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