# Which solution has higher boiling point?

Between a 2% (w/v) aqueous solutions of $$\ce{NaCl}$$ and $$\ce{RbCl}$$, which will have a higher boiling point. Here there are two competing factors. First there's the fact that $$\ce{NaCl}$$ has a higher concentration. So it's solution should have a higher boiling point. Secondly according to Fajan's rule, $$\ce{NaCl}$$ is more polarised. So it should have a lower boiling point. So which factor is dominant?

• Fajans is irrelevant. Both compounds are going to be fully dissociated anyway. – Ivan Neretin Feb 14 '19 at 12:56
• Which solution has the higher molar concentration? – matt_black Feb 14 '19 at 16:36

Molar mass of $$\ce{RbCl}$$ is $$\pu{120.92 g/mol}$$, Molar mass of $$\ce{NaCl}$$ is $$\pu{58.44 g/mol}$$. Both compounds are highly ionic and dissociate in water solutions. Thus, 2% solution of $$\ce{NaCl}$$ has approximately double amount of ions than that in 2% solution of $$\ce{RbCl}$$ (2% is fairly dilute as well, considering their solubility in water). Thus, theoretically, the $$\ce{NaCl}$$ solution should have higher boiling point (higher solute particles).