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

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.