Common Questions

Question 1

Why is CF4 soluble in water?

Answer 1

Structure→Polarity→IMF→Energy

• CF 4 and water have simple molecular structure
• CF 4 is non-polar with id-id interactions between the molecules
• Water is polar and hydrogen bonds exist between H2O molecules.
• energy evolved when CF 4 molecules form id-id interactions with water molecules insufficient to overcome the hydrogen bonds between H2O molecules and the id-id interactions between the CF4 molecules

Question 2

Why CH3SCH3 has a higher boiling point than CH3OCH3?

Answer 2

Structure→Polarity→IMF→Energy

• Both have simple molecular structure and are polar with pd-pd interactions and id-id interactions between molecules
• CH3SCH3 has a larger electron cloud than CH3OCH3 and electron cloud is polarised to a larger extent → stronger id-id interactions between molecules
• more energy needed to overcome stronger id-id bond, higher bp

Question 3

Why N2H4 has a higher boiling point than NH3?

Answer 3

• hydrazine (contains 2 N atom), able to form 2 intermolecular hydrogen bonds per molecule
• ammonia can only form 1 intermolecular hydrogen bonds per molecule
• **more energy **is required to break the more extensive intermolecular hydrogen bonding present in hydrazine

MUST WRITE PER MOLECULE TO GET MARK!

Question 4

What are the 3 assumptions of Ideal Gas?

Answer 4

1. Ideal gas molecules take up negligible volume as compared to the volume of the container
2. Ideal gas molecules have negligible intermolecular forces of attraction
3. Collisions between ideal gas molecules are perfectly elastic

Question 5

What are factors that deviation gases from ideal gas behaviour?

Answer 5

• larger electron cloud size, id-id not negligible
• molecules are large, volume of molecule not negligible compared to the volume of container

Question 6

How can gas to approach ideal behavior?

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Answer 6

• high temperature, gas particles have higher kinetic energy
• gas particles have enough energy to overcome imf, imf negligible, approaches ideal behaviour.
• low pressure, gas particles are further apart, imf less significant, imf neligible
• molecular size of the gas particles to be negligible comapred to the volume of container, approaches ideal behaviour

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Question 7

why does NH3 deviate more from ideal gas than CH3?

Answer 7

• NH 3 molecules are held by stronger intermolecular hydrogen bond between the NH 3 molecules as compared to weaker instantaneous dipole–induced dipole (id-id) interactions between CH 4 molecules.
• Intermolecular forces of attraction between NH 3 molecules are more significant and deviate more from ideal gas

Question 8

How does id-id form in CO2?

Answer 8

• e- in random motion,→ uneven distribution of electrons in molecule
  → separation of charges and creates an instantaneous dipole in the CO2 molecule
• instantaneous dipole induces formation of dipoles in the neighbouring unpolarised CO2 molecules
• weak electrostatic forces of attraction (instantaneous dipole – induced dipole interactions) forms between two dipoles

Question 9

How does pd-pd form in HCl?

Answer 9

• e- in random motion,→ uneven distribution of electrons in molecule
  → separation of charges and creates an instantaneous dipole in the CO2 molecule
• instantaneous dipole induces formation of dipoles in the neighbouring unpolarised CO2 molecules
• weak electrostatic forces of attraction (permanent dipole – permanent dipole interactions) forms between two dipoles

Question 10

How does H2 Bond form in NH3?

Answer 10

• N atom more electronegative than H atom, attracts bonding e- in the N−H bond
• N atom gains a partial negative charge, H atom acquires a partial positive charge
• electrostatic attraction (hydrogen bond) between the e- deficient H atom of one NH3 molecule and the lone pair of e- on N atom on another NH 3 molecule