Q26 of 53 Page 59

If the density of some lake water is 1.25g/ml and contains 92 g of Na+ ions per kg of water, calculate the molality of Na+ ions in the lake.

Mass of ions = 92g


Molar mass of ions = Na+ = 23g(neglect the mass lost due to absence of a electron)


Moles of ions = mass of ions/molar mass


⇒ n = 92/23 moles


⇒ n = 4moles


Molality of solution = moles of solute/mass of solvent(in kg)


Molality = 4/1 = 4M


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