CHEMISTRY 31

Quiz 1 - Solutions

Feb. 4, 2015

 

The actinide thorium (Th) reacts with fluoride as: Th4+ + 4F- => ThF4. If 25.0 mL of 0.0246 M Th4+ are added to an HF solution,

a) calculate the moles of F- reacted if the reaction goes to completion.

n(F-)/n(Th4+) = 4/1 or n(F-) = 4n(Th4+) = 4(25.0 mL)(0.0246 mol/L)(10-3 L/1 mL)

n(F-) = 2.46 x 10-3 mol

 

b) calculate the mass (in g) of a 0.521 wt % aqueous HF solution needed to provide the moles of F- in a).† The formula weight of HF is 20.01 g/mol

mass(HF) = (2.46 x 10-3 mol)(20.01 g/mol) = 0.04922 g HF

0.521 wt % aqueous HF solution means 0.521 g HF/100 g solín

mass solín = (0.04922 g HF)(100 g solín/0.521 g HF) = 9.45 g