Drops of mercury, water and naphtha (lighter fluid) are placed on smooth flat surface. The mercury drop is almost a perfect sphere. The water drop is a flattened sphere. The naphtha however spreads out over the surface. What do these observations tell you about the cohesive force in mercury water and naphtha?
(b) Which liquid would vaporize easiest?
(c) Which would have the lowest boiling point? Explain.
Here is a good site for reading about cohesive versus adhesive forces. As you can see the cohesive forces for mercury are highest, water is next, and the cohesion among naphtha molecules is very low. After reading the article you should be able to answer the questions.
http://en.wikipedia.org/wiki/Cohesion_(chemistry)
Yeah
From the question Naphtha is least cohesive and most adhesive. Whereas mercury is the exact opposite. Water is in the middle of these two.
But does it necessarily mean that the liquid which is the most adhesive will vapourize easiest and have the lowest boiling point?
I don't think I would express it in the form of adhesive but rather in cohesive. It does stand to reason that the liquid with the most cohesive forces (those between the same molecules) will have the highest boiling point and those with the least cohesiveness will have the lowest boiling point.
Based on the evidence included in the question, cohesive forces (attraction between particles within a material) decrease: Hg > H2O > naphtha.
Next, consider how the boiling point is related to cohesive forces and deduce whether the boiling points compare in the same way or in the reverse way.
The observations of the drops of mercury, water, and naphtha on a smooth flat surface can provide insights into the cohesive forces within these liquids.
(a) Cohesive forces refer to the intermolecular attractions or forces that hold the molecules of a substance together. They determine the behavior of a liquid and its ability to form drops and maintain a specific shape.
Based on the provided information:
1. Mercury drop: The fact that the mercury drop forms a nearly perfect spherical shape indicates that mercury has strong cohesive forces. The cohesive forces between mercury molecules are significant, resulting in a high surface tension, which allows it to resist spreading and retain a spherical shape.
2. Water drop: The flattened shape of the water drop signifies weaker cohesive forces compared to mercury. Water has moderate cohesive forces, allowing it to form a somewhat spherical shape but with a slight flattening due to gravitational forces.
3. Naphtha drop: The way naphtha spreads out over the surface suggests that it has very weak cohesive forces. Naphtha has low surface tension due to weak intermolecular forces, which results in poor cohesion and a tendency to quickly spread out rather than form drops.
In summary, the observations indicate that mercury has the highest cohesive forces, followed by water, and then naphtha with the weakest cohesive forces.
(b) The ease of vaporization depends on various factors, including the strength of intermolecular forces and the boiling points of the liquids.
Naphtha, being a lighter fluid, tends to vaporize more easily than both mercury and water. This is because it has the weakest cohesive forces among the three liquids. Weak intermolecular forces make it easier for the molecules at the liquid's surface to overcome these forces and transition into the vapor phase.
(c) The boiling point of a liquid is determined by the strength of its intermolecular forces. Generally, higher boiling points indicate stronger cohesive forces.
Based on the observations and the cohesive force trends mentioned earlier, we can make an inference about the boiling points:
- Mercury, having the strongest cohesive forces, would be expected to have the highest boiling point among the three liquids.
- Water, with moderately strong cohesive forces, would have a boiling point lower than mercury but higher than naphtha.
- Naphtha, having the weakest cohesive forces, would be expected to have the lowest boiling point among the three liquids.
It is important to note that the boiling points can be influenced by other factors as well, including molecular weight, polarity, and presence of impurities.