which pair of substances are most likely to obey Raoult's Law?

C5H12 and C6H14
H3PO4 and H20
C4H9COOH and C5H12
C5H12 and H20
C4H9COOH and H20

How do I go about figuring this out? What should I be comparing, differences in molar masses, polarity, etc...?

To determine which pair of substances are most likely to obey Raoult's Law, you should compare the differences in the nature of the molecules, particularly their interactions with each other. Raoult's Law applies to ideal solutions, where the behavior of the components is similar to an ideal gas.

Key factors to consider are the similarities in molecular size, shape, and intermolecular forces between the two substances. In ideal solutions, the components should have similar molecular size, shape, and intermolecular forces for Raoult's Law to hold true.

Comparing the given pairs of substances, let's analyze each one:

1. C5H12 and C6H14:
- Both substances are hydrocarbons, belonging to the alkane group.
- They have similar molecular sizes and similar intermolecular forces (van der Waals forces).
- Therefore, they are likely to obey Raoult's Law.

2. H3PO4 and H2O:
- H3PO4 is a polar molecule due to its acidic properties, while H2O is a highly polar molecule.
- They have significantly different molecular sizes and different types of intermolecular forces (hydrogen bonding in H2O).
- Therefore, they are less likely to obey Raoult's Law.

3. C4H9COOH and C5H12:
- C4H9COOH is a carboxylic acid, while C5H12 is an alkane.
- They have different molecular sizes and different types of intermolecular forces (hydrogen bonding in C4H9COOH).
- Therefore, they are less likely to obey Raoult's Law.

4. C5H12 and H2O:
- C5H12 is an alkane, while H2O is a highly polar molecule.
- They have different molecular sizes and different types of intermolecular forces (hydrogen bonding in H2O).
- Therefore, they are less likely to obey Raoult's Law.

5. C4H9COOH and H2O:
- C4H9COOH is a carboxylic acid, while H2O is a highly polar molecule.
- They have different molecular sizes and different types of intermolecular forces (hydrogen bonding in both substances).
- Therefore, they are less likely to obey Raoult's Law.

In summary, the pair of substances most likely to obey Raoult's Law is C5H12 and C6H14, as they have similar molecular sizes and similar intermolecular forces.

To determine which pair of substances is most likely to obey Raoult's Law, you need to compare the similarities in the intermolecular forces and molecular interactions between the substances.

Raoult's Law states that in an ideal solution, the partial pressure of each component in the vapor phase is directly proportional to its mole fraction in the liquid phase. This law assumes that the intermolecular forces between the components are similar.

When comparing the substances, there are a few factors you should consider:

1. Similarity in molecular size: Usually, substances with similar molar masses have similar magnitudes of intermolecular forces, making them more likely to obey Raoult's Law.
2. Similarity in intermolecular forces: Substances with similar types of intermolecular forces (e.g., hydrogen bonding, dipole-dipole interactions, van der Waals forces) are more likely to obey Raoult's Law.
3. Similarity in polarity: Substances with similar polarities are more likely to have comparable intermolecular forces and therefore follow Raoult's Law.

Now, let's compare the given pairs of substances:

a) C5H12 (pentane) and C6H14 (hexane):
These two substances have similar molecular sizes and exhibit only weak van der Waals forces. Therefore, they are likely to obey Raoult's Law.

b) H3PO4 (phosphoric acid) and H2O (water):
Phosphoric acid is a polar molecule and exhibits hydrogen bonding, while water is also polar and shows extensive hydrogen bonding. Even though they have different molar masses, their similar polarities and intermolecular forces make them likely to obey Raoult's Law.

c) C4H9COOH (butanoic acid) and C5H12 (pentane):
Butanoic acid is a larger molecule and exhibits stronger intermolecular forces, including hydrogen bonding. In contrast, pentane is a smaller nonpolar molecule with only van der Waals forces. Due to their dissimilar intermolecular forces, they are less likely to obey Raoult's Law.

d) C5H12 (pentane) and H2O (water):
As mentioned earlier, pentane is a nonpolar molecule, while water is polar. They have different molecular sizes, polarities, and intermolecular forces. Hence, they are less likely to obey Raoult's Law.

e) C4H9COOH (butanoic acid) and H2O (water):
Both butanoic acid and water are polar molecules and exhibit hydrogen bonding. They have different molecular sizes but similar intermolecular forces. Therefore, they are likely to obey Raoult's Law.

Based on the above explanations, the pair of substances most likely to obey Raoult's Law is C5H12 (pentane) and C6H14 (hexane).

I would choose substances that are alike in ability to dissove miscibily.

Pentane and water is no..for example.

Butanoic acid and pentane is another not likely to dissolve.