lls off a duck\'s back but thoroughly wets a head of 4 ir. What do these observa
ID: 229673 • Letter: L
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lls off a duck's back but thoroughly wets a head of 4 ir. What do these observations reveal about the chemical nature of these two surfaces? 16. Why do raindrops not assume triangular or cubic shapes? 7. How does perspiration cool the skin on a person's body? tube Why does the surface of water in a glass test tube curve is upward at the 18. upward at the edges? 19. Automobile engines are designed to be lubricated with motor oils of specific viscosities. These are rated from the lowest viscosity of 5 W up to the highest viscosity of 70 W. What can you conclude about the intermolecular attractions in an oil rated 10W? 20. What is the essential difference between boiling and evaporation? 21. Water in a trucks radiator can get hotter than 100 °C when the radiator is sealed tightly. How is it possible for water to exist as a liquid at temperatures above its normal boiling point?Explanation / Answer
15. Water mix with hair to become wet. But ducks secret a oil which is applied on their back. And as water and oil are least soluble, thus they don't mix and they remain dry. This reveals that the adhesive forces are stronger in case of our hair, but with oil cohesive forces are stronger.
16. The water molecules on the surface have higher energy than in the bulk due to surface tension. Thus they tend to form the shape of least area in uniform fluid. As sphere has the least area, thus this shape is assumed.
17. During perspiration water droplets on the surface of the body evaporates and takes some amount of body heat. Thus we feel cooler.
18. For water adhesive forces are stronger than the cohesive forces between the molecules. Thus the molecules of water sticking to the test tube, rise up a little due to capillary action.
19. Oil rated 10W has very low viscosity. Thus this oil has stronger cohesive forces than adhesive forces. The flow seen is due to capillary action of oil on any surface. Thus as viscosity is low, capillary action is low which means adhesive forces are not as strong as cohesive forces.
20. Boiling is a bulk phenomenon where water molecule present anywhere in the system can get energy more than threshold energy and escape. But in evaporation only the surface molecules can gain energy to escape. Also boiling requires external supply of heat but evaporation is a natural phenomena.
21. The water used in radiators contain a mixture of water and some other chemicals. Thus the boiling point of water is increased due to presence of impurities.
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