Melting point Q

[Addallat]

Base soley upon their relative intermolecular attractions which one of the following ionic solids might have the highest melting point?

A. Na2O
B. BaO
C. KF
D. AgCl

Correct answer was A

My thought process: Why isn't this approached as a colligative property?

Viewed this as a melting point depression, and since AgCl has a van't hoff factor of 1 while the other answer choices have a van't hoff factor >1 therefore AgCl must have the highest melting point

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[Hadi7183]

Viewed this as a melting point depression

The question doesn't talk about a SOLUTION of these salts, rather it asks about the salt in its SOLID state. You basically need to look at the force between ions. I think the correct answer is B, because Ba2+ and O2- carry greater charges and therefore the electrostatic force responsible for crystal formation is stronger.

 

[techfan]

Because you're asked about the solid, not an aqueous solution. Also are you sure you're not getting boiling point elevation and freezing point depression mixed up with melting point depression? I don't think van't Hoff factor plays a role in melting point depression since melting point depression is due to impurities.

I'm pretty sure this question is trying to get you to use atomic size and charge difference. Is the answer B?

 

[erythrocyte666]

Answer A makes sense because I would expect the smaller size of Na ions to be more significant than the greater charge on the Ba ions

 

[chemtopper]

Base soley upon their relative intermolecular attractions which one of the following ionic solids might have the highest melting point?

A. Na2O
B. BaO
C. KF
D. AgCl

Correct answer was A

My thought process: Why isn't this approached as a colligative property?

Viewed this as a melting point depression, and since AgCl has a van't hoff factor of 1 while the other answer choices have a van't hoff factor >1 therefore AgCl must have the highest melting point

Colligative properties are with impurities in the solvent or in some other solids not for pure substances.This question is based on the knowledge about lattice energy.Lattice energy is directly proportional to the charges and inversely
proportional to the size of the ion.If we work on the charges ... AgCl and KF are ruled out as they have only +1 and -1 charges ,Now we are left with Na2O and BaO. O2- is same in both cases so just compare Na+ and Ba2+.Ba2+ is bigger in size than Na+ ion .So in this case Na2O has higher MPt

 

[Addallat]

answer was A

Colligative properties are with impurities in the solvent or in some other solids not for pure substances.This question is based on the knowledge about lattice energy.Lattice energy is directly proportional to the charges and inversely
proportional to the size of the ion.If we work on the charges ... AgCl and KF are ruled out as they have only +1 and -1 charges ,Now we are left with Na2O and BaO. O2- is same in both cases so just compare Na+ and Ba2+.Ba2+ is bigger in size than Na+ ion .So in this case Na2O has higher MPt

wow thank you fantastic explanation