The freezing point and the boiling point of water can be altered by a variety of
techniques.

which of the following has little or no effect on the boiling point of water?

a. increasing the air pressure above the liquid
b. adding alcohol to the water
c. adding sodium chloride to the water
d. increasing the amount of water

Explanation:

The boiling point is defined as the tempearature at which the vapor pressure of a substance equals the atmospheric pressure.

The vapor pressure is the pressure exerted by the vapor particles above the liquid in a sealed container.

In order to a liquid boil, the particles must have enough kinetic energy to escape from the tliquid to the gas (vapor) phase. With that we can approach the choices:

a. Increasing the air pressure above the lquid.

Incorrect choice.

If the air pressure above the liquids is increased, then the liquid particles will need more energy to escape, which means that this change has a considerable effect on increasing the boiling point.

b. Adding alcohol to the water.

Incorrect choice.

The alcohol  added to the water is a solute. Some of the particles of the alcohol added will ocuppy part of the surface of liquid, reducing the number of particles of water that can escape from the liquid phase to the gas state. This reduces the vapor pressure and cause that the boiling point increase. Then, adding alcohol to the water does has an effect on the boiling point (the boiling point will increase).

c. Adding sodium chloride to the water.

Incorrect choice.

As in the case of adding alcohol, sodium chloride is a solute. Thus, the same analysis drives the condlusion that adding sodium chloride to the water does has an effect on the boiling point (the boiling point will increase).

d. Increasing the amount of water.

Correct choice.

The boiling point is a specific property of the substance: it does not depend on the amount of substance. Then, increasing the amount of water will not affect the boiling point.

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