Question

liquid a is known to have a lower vapor pressure and lower surface tension than liquid b. use these facts to predict the result of each experiment in the table below, if you can.

experiment	predicted outcome

| 10.0 ml of liquid a are put in one sealed 5 l flask, and 10.0 ml of liquid b are put in another sealed 5 l flask. the pressure in each flask is slowly increased by pumping in argon gas. | - eventually both liquids boil, a first and then b.

• eventually both liquids boil, b first and then a.
• neither liquid will boil
• its impossible to predict whether eitherliquid boils without more information. |

| identical wire loops are dipped into liquid a and liquid b, so that a film of liquid forms across the loops (like the bubble solution on a childs bubble blowing wand). the width of each loop is increased slowly and the forces ( f_a ) and ( f_b ) needed to make the loops 5% wider are measured. | - ( f_a ) will be greater than ( f_b )

• ( f_a ) will be less than ( f_b )
• ( f_a ) will be equal to ( f_b )
• its impossible to predict whether ( f_a ) or ( f_b ) will be greater without more information. |

Explanation:

Experiment 1:

Step 1: Understand the relationship between vapor - pressure and boiling

Boiling occurs when the vapor pressure of a liquid equals the external pressure. A liquid with lower vapor pressure requires a higher external pressure to reach its boiling point. Since Liquid A has a lower vapor pressure than Liquid B, when the external pressure is increased (by pumping in argon gas), Liquid B will reach its boiling point (vapor pressure = external pressure) at a lower external pressure compared to Liquid A.

Step 2: Predict the boiling order

So, eventually both liquids boil, B first and then A.

Experiment 2:

Step 1: Recall the relationship between surface tension and the force to expand a liquid film

The force \(F\) required to expand a liquid film (in this case, the liquid film across the wire loop) is related to the surface tension \(\gamma\) by the formula \(F = 2\gamma l\) (where \(l\) is the length of the wire in contact with the liquid, and the factor of 2 comes from the two - sided nature of the liquid film).

Step 2: Compare the forces based on surface tension

Since Liquid A has a lower surface tension (\(\gamma_A<\gamma_B\)) and the loops are identical (so \(l\) is the same for both), using the formula \(F = 2\gamma l\), we can say that \(F_A\) (force for Liquid A) will be less than \(F_B\) (force for Liquid B)

Answer:

• For the first experiment: Eventually both liquids boil, B first and then A.
• For the second experiment: \(F_A\) will be less than \(F_B\)