The freezing point depression constant for water is `= 1.86^@C` m . If 5.00 g `Na SO_4` is dissolved in 45.0 g H,O, the freezing point is changed by `-3.82^@C`. Calculate the van't Hoff factor for `Na SO_4`

Options

A. 2.05
B. 2.63
C. 3.11
D. 0.381

Answer

B

Explanation

We know that, `DeltaT_f =ixx k_f xx(w_Bxx1000)/(m_Bxxw_A)`
Given : `DeltaT_f = 3.82, K_f= 1.86`
`w_f = 5, m_B = 142, w_A= 45`
`(DeltaT_f xx m_Bxxw_A)/(K_f xxw_Bxx1000) = (3.82xx142 xx 45)/(1.86 xx 5 xx 1000) = 2.63`