Passage IV

Atmospheres (atm), torr, and kilopascals (kPa) are common units of pressure. Figure 1 can be used to convert between torr and kPa. A pressure of 1 atm is indicated in Figure 1.

Figure 2 shows how boiling point (BP) varies with atmospheric pressure for 3 compounds: acetaldehyde, ace­tone, and pentane. The unit of pressure is torr.

Figure 3 shows how BP varies with atmospheric pres­sure for 3 other compounds: ethanol, methanol, and methyl acetate. The unit of pressure is kPa.

26. Suppose a sample of methanol is in a chamber maintained at 60°C and 110 kPa. Based on Figure 3, if the temperature is kept constant, which of the following changes in the pressure will cause the sample to boil?

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

From figures 2 & 3, it can be seen that the lower the pressure, the lower the boiling point;

In the case of constant temperature, by changing the pressure, let methanol boil, indicating that the methanol needs to be reduced boiling point, then only by reducing the pressure can the boiling point be reduced to 60°C;

Look at figure 3, when the ordinate BP of methanol is 60°C, the abscissa pressure is 85 kPa, 110-85 =25 kPa, so as long as the pressure is lowered by more than 25 kPa, the boiling point of methanol can be lowered below 60°C, so that methanol boils