Question

(a) Differentiate between molarity and molality for a solution. How does a change in temperature influence their values ?
(b) Calculate the freezing point of an aqueous solution containing `10.50g` of `MgBr_(2)` in `200g` of water. (Molar mass of `MgBr_(2)=184g`) (`K_(f)` for waer `=1.86K kg "mol"^(-1)`)

Answer 1

(a) See Q. 13, Set-I, Delhi Board, 2009.
(b) Molecular mass of `MgBr_2` = 184g
`i=3asMgBr_2toMg^(2+)+2Br^-`
`DeltaT_f=i(K_fxxW_Bxx1000)/(M_BxxW_A)=(1.86xx10.50xx1000xx3)/(184xx200)=1.592k`
Freezing point of solution (Ts)
`=273-1.592=271.408K`