Asalt is known to be an alkali metal fluoride. a quick approximate determination of freezing point indicates that 4 g of the salt dissolved in 100 g of water produces a solution that freezes at about −1.4 °c. what is the formula of the salt? show your calculations.

RbF

Explanation:

Depression in freezing point is given by:

= Depression in freezing point

i= vant hoff factor = 2 (for alkali metal flouride, MF)

= freezing point constant =

m= molality

Weight of solvent (water)= 100 g = 0.1 kg  

Molar mass of unknown solute = ? g/mol

Mass of unknown solute added = 4 g

Thus the mass of is 106 g/mol

x + 19 = 106

x = 87 g

Thus the atomic mass is near to that of rubidium, thus the formula of the salt is

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