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Chemistry and Liquids Help

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By — McGraw-Hill Professional
Updated on Aug 28, 2011

Introduction to Liquids

Lava, a cold mountain stream, and mercury are all liquids. They are very different, with different compositions and different standard temperatures, but they are all members of the in-between element club, known as the liquids. The members of this club are affected by environment much more than solids. Sometimes the difference of a few degrees of temperature can cause an element to slip from being a member of the solid club to new membership in the liquid club. Cesium has a particularly great trick of switching from a solid to a liquid. It is solid at room temperature, but when held in the hand and heated to body temperature of 98.6°F, it melts and becomes a liquid.

A chocolate bar does the same thing. On the shelf at room temperature, it’s a solid, but when held in the hand and heated to body temperature, it melts.

Density

Liquids are less dense than tightly packed solids. The density of a liquid affects the way a liquid acts. It has different characteristics from solids, like the ability to flow across a table top when spilled.

Table 16.1 Liquids are the stars of the in-between club of matter.

Table 16.1 gives some general characteristics of liquids.

Liquids

Fixed volume

Loose structure

Cannot be tightly compressed

Have different viscosities or resistances to flow

Held together by surface tension

Miscible or immiscible

Expand and vaporize when heated

Unequal molecular bonding

Medium density

 

The density of water is 1.00 g/ml at 4°C. The metric system of measuring liquid density is based on this number. When comparing the density of liquids, generally they can be compared to water. This makes it easier to figure out whether liquids will mix or not, since two liquids of very different densities don’t usually combine.

There are exceptions. Very dense ionic solutions like salt water will dissolve in water since both are polar. Oil which is non-polar will not dissolve in water even if the densities were close to each other. Their failure to mix is due to their properties, rather than density.

For example, the densities of mercury (13.5 g/ml) and water (1.0 g/ml) are very different relative to each other. This relative density difference (sometimes called specific gravity) causes mercury to sink to the bottom of a container filled with water.

Relative density (specific gravity) is the ratio of the density of a sample at 20°C divided by the density of water at 4°C.

Some of the physical characteristics that affect liquids are viscosity, surface tension, boiling point, vaporization, condensation, and evaporation. These are described below.

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